[PATCH v2 bpf-next 00/13] Atomics for eBPF

[PATCH v2 bpf-next 00/13] Atomics for eBPF

[Brendan Jackman]

Status of the patches
=====================

Thanks for the reviews! Differences from v1->v2 [1]:

* Fixed mistakes in the netronome driver

* Addd sub, add, or, xor operations

* The above led to some refactors to keep things readable. (Maybe I
  should have just waited until I'd implemented these before starting
  the review...)

* Replaced BPF_[CMP]SET | BPF_FETCH with just BPF_[CMP]XCHG, which
  include the BPF_FETCH flag

* Added a bit of documentation. Suggestions welcome for more places
  to dump this info...

The prog_test that's added depends on Clang/LLVM features added by
Yonghong in https://reviews.llvm.org/D72184

This only includes a JIT implementation for x86_64 - I don't plan to
implement JIT support myself for other architectures.

Operations
==========

This patchset adds atomic operations to the eBPF instruction set. The
use-case that motivated this work was a trivial and efficient way to
generate globally-unique cookies in BPF progs, but I think it's
obvious that these features are pretty widely applicable.  The
instructions that are added here can be summarised with this list of
kernel operations:

* atomic[64]_[fetch_]add
* atomic[64]_[fetch_]sub
* atomic[64]_[fetch_]and
* atomic[64]_[fetch_]or
* atomic[64]_xchg
* atomic[64]_cmpxchg

The following are left out of scope for this effort:

* 16 and 8 bit operations
* Explicit memory barriers

Encoding
========

I originally planned to add new values for bpf_insn.opcode. This was
rather unpleasant: the opcode space has holes in it but no entire
instruction classes[2]. Yonghong Song had a better idea: use the
immediate field of the existing STX XADD instruction to encode the
operation. This works nicely, without breaking existing programs,
because the immediate field is currently reserved-must-be-zero, and
extra-nicely because BPF_ADD happens to be zero.

Note that this of course makes immediate-source atomic operations
impossible. It's hard to imagine a measurable speedup from such
instructions, and if it existed it would certainly not benefit x86,
which has no support for them.

The BPF_OP opcode fields are re-used in the immediate, and an
additional flag BPF_FETCH is used to mark instructions that should
fetch a pre-modification value from memory.

So, BPF_XADD is now called BPF_ATOMIC (the old name is kept to avoid
breaking userspace builds), and where we previously had .imm = 0, we
now have .imm = BPF_ADD (which is 0).

Operands
========

Reg-source eBPF instructions only have two operands, while these
atomic operations have up to four. To avoid needing to encode
additional operands, then:

- One of the input registers is re-used as an output register
  (e.g. atomic_fetch_add both reads from and writes to the source
  register).

- Where necessary (i.e. for cmpxchg) , R0 is "hard-coded" as one of
  the operands.

This approach also allows the new eBPF instructions to map directly
to single x86 instructions.

[1] Previous patchset:
    https://lore.kernel.org/bpf/20201123173202.1335708-1-jackmanb@google.com/

[2] Visualisation of eBPF opcode space:
    https://gist.github.com/bjackman/00fdad2d5dfff601c1918bc29b16e778


Brendan Jackman (13):
  bpf: x86: Factor out emission of ModR/M for *(reg + off)
  bpf: x86: Factor out emission of REX byte
  bpf: x86: Factor out function to emit NEG
  bpf: x86: Factor out a lookup table for some ALU opcodes
  bpf: Rename BPF_XADD and prepare to encode other atomics in .imm
  bpf: Move BPF_STX reserved field check into BPF_STX verifier code
  bpf: Add BPF_FETCH field / create atomic_fetch_add instruction
  bpf: Add instructions for atomic_[cmp]xchg
  bpf: Pull out a macro for interpreting atomic ALU operations
  bpf: Add instructions for atomic[64]_[fetch_]sub
  bpf: Add bitwise atomic instructions
  bpf: Add tests for new BPF atomic operations
  bpf: Document new atomic instructions

 Documentation/networking/filter.rst           |  57 ++-
 arch/arm/net/bpf_jit_32.c                     |   7 +-
 arch/arm64/net/bpf_jit_comp.c                 |  16 +-
 arch/mips/net/ebpf_jit.c                      |  11 +-
 arch/powerpc/net/bpf_jit_comp64.c             |  25 +-
 arch/riscv/net/bpf_jit_comp32.c               |  20 +-
 arch/riscv/net/bpf_jit_comp64.c               |  16 +-
 arch/s390/net/bpf_jit_comp.c                  |  27 +-
 arch/sparc/net/bpf_jit_comp_64.c              |  17 +-
 arch/x86/net/bpf_jit_comp.c                   | 252 ++++++++++----
 arch/x86/net/bpf_jit_comp32.c                 |   6 +-
 drivers/net/ethernet/netronome/nfp/bpf/jit.c  |  14 +-
 drivers/net/ethernet/netronome/nfp/bpf/main.h |   4 +-
 .../net/ethernet/netronome/nfp/bpf/verifier.c |  15 +-
 include/linux/filter.h                        | 117 ++++++-
 include/uapi/linux/bpf.h                      |   8 +-
 kernel/bpf/core.c                             |  67 +++-
 kernel/bpf/disasm.c                           |  41 ++-
 kernel/bpf/verifier.c                         |  77 +++-
 lib/test_bpf.c                                |   2 +-
 samples/bpf/bpf_insn.h                        |   4 +-
 samples/bpf/sock_example.c                    |   2 +-
 samples/bpf/test_cgrp2_attach.c               |   4 +-
 tools/include/linux/filter.h                  | 117 ++++++-
 tools/include/uapi/linux/bpf.h                |   8 +-
 tools/testing/selftests/bpf/Makefile          |  12 +-
 .../selftests/bpf/prog_tests/atomics_test.c   | 329 ++++++++++++++++++
 .../bpf/prog_tests/cgroup_attach_multi.c      |   4 +-
 .../selftests/bpf/progs/atomics_test.c        | 124 +++++++
 .../selftests/bpf/verifier/atomic_and.c       |  77 ++++
 .../selftests/bpf/verifier/atomic_cmpxchg.c   |  96 +++++
 .../selftests/bpf/verifier/atomic_fetch_add.c | 106 ++++++
 .../selftests/bpf/verifier/atomic_or.c        |  77 ++++
 .../selftests/bpf/verifier/atomic_sub.c       |  44 +++
 .../selftests/bpf/verifier/atomic_xchg.c      |  46 +++
 .../selftests/bpf/verifier/atomic_xor.c       |  77 ++++
 tools/testing/selftests/bpf/verifier/ctx.c    |   7 +-
 .../testing/selftests/bpf/verifier/leak_ptr.c |   4 +-
 tools/testing/selftests/bpf/verifier/unpriv.c |   3 +-
 tools/testing/selftests/bpf/verifier/xadd.c   |   2 +-
 40 files changed, 1754 insertions(+), 188 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/atomics_test.c
 create mode 100644 tools/testing/selftests/bpf/progs/atomics_test.c
 create mode 100644 tools/testing/selftests/bpf/verifier/atomic_and.c
 create mode 100644 tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c
 create mode 100644 tools/testing/selftests/bpf/verifier/atomic_fetch_add.c
 create mode 100644 tools/testing/selftests/bpf/verifier/atomic_or.c
 create mode 100644 tools/testing/selftests/bpf/verifier/atomic_sub.c
 create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xchg.c
 create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xor.c

--
2.29.2.454.gaff20da3a2-goog

[PATCH v2 bpf-next 01/13] bpf: x86: Factor out emission of ModR/M for *(reg + off)

[Brendan Jackman]

The case for JITing atomics is about to get more complicated. Let's
factor out some common code to make the review and result more
readable.

NB the atomics code doesn't yet use the new helper - a subsequent
patch will add its use as a side-effect of other changes.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 arch/x86/net/bpf_jit_comp.c | 42 +++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 18 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 796506dcfc42..94b17bd30e00 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -681,6 +681,27 @@ static void emit_mov_reg(u8 **pprog, bool is64, u32 dst_reg, u32 src_reg)
 	*pprog = prog;
 }
 
+/* Emit the ModR/M byte for addressing *(r1 + off) and r2 */
+static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off)
+{
+	u8 *prog = *pprog;
+	int cnt = 0;
+
+	if (is_imm8(off)) {
+		/* 1-byte signed displacement.
+		 *
+		 * If off == 0 we could skip this and save one extra byte, but
+		 * special case of x86 R13 which always needs an offset is not
+		 * worth the hassle
+		 */
+		EMIT2(add_2reg(0x40, r1, r2), off);
+	} else {
+		/* 4-byte signed displacement */
+		EMIT1_off32(add_2reg(0x80, r1, r2), off);
+	}
+	*pprog = prog;
+}
+
 /* LDX: dst_reg = *(u8*)(src_reg + off) */
 static void emit_ldx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
 {
@@ -708,15 +729,7 @@ static void emit_ldx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
 		EMIT2(add_2mod(0x48, src_reg, dst_reg), 0x8B);
 		break;
 	}
-	/*
-	 * If insn->off == 0 we can save one extra byte, but
-	 * special case of x86 R13 which always needs an offset
-	 * is not worth the hassle
-	 */
-	if (is_imm8(off))
-		EMIT2(add_2reg(0x40, src_reg, dst_reg), off);
-	else
-		EMIT1_off32(add_2reg(0x80, src_reg, dst_reg), off);
+	emit_modrm_dstoff(&prog, src_reg, dst_reg, off);
 	*pprog = prog;
 }
 
@@ -751,10 +764,7 @@ static void emit_stx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
 		EMIT2(add_2mod(0x48, dst_reg, src_reg), 0x89);
 		break;
 	}
-	if (is_imm8(off))
-		EMIT2(add_2reg(0x40, dst_reg, src_reg), off);
-	else
-		EMIT1_off32(add_2reg(0x80, dst_reg, src_reg), off);
+	emit_modrm_dstoff(&prog, dst_reg, src_reg, off);
 	*pprog = prog;
 }
 
@@ -1240,11 +1250,7 @@ st:			if (is_imm8(insn->off))
 			goto xadd;
 		case BPF_STX | BPF_XADD | BPF_DW:
 			EMIT3(0xF0, add_2mod(0x48, dst_reg, src_reg), 0x01);
-xadd:			if (is_imm8(insn->off))
-				EMIT2(add_2reg(0x40, dst_reg, src_reg), insn->off);
-			else
-				EMIT1_off32(add_2reg(0x80, dst_reg, src_reg),
-					    insn->off);
+xadd:			emit_modrm_dstoff(&prog, dst_reg, src_reg, insn->off);
 			break;
 
 			/* call */
-- 
2.29.2.454.gaff20da3a2-goog

Re: [PATCH v2 bpf-next 01/13] bpf: x86: Factor out emission of ModR/M for *(reg + off)

[Alexei Starovoitov]

On Fri, Nov 27, 2020 at 05:57:26PM +0000, Brendan Jackman wrote:
> +/* Emit the ModR/M byte for addressing *(r1 + off) and r2 */
> +static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off)

same concern as in the another patch. If you could avoid intel's puzzling names
like above it will make reviewing the patch easier.

Re: [PATCH v2 bpf-next 01/13] bpf: x86: Factor out emission of ModR/M for *(reg + off)

[Brendan Jackman]

On Sat, Nov 28, 2020 at 05:15:52PM -0800, Alexei Starovoitov wrote:
> On Fri, Nov 27, 2020 at 05:57:26PM +0000, Brendan Jackman wrote:
> > +/* Emit the ModR/M byte for addressing *(r1 + off) and r2 */
> > +static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off)
> 
> same concern as in the another patch. If you could avoid intel's puzzling names
> like above it will make reviewing the patch easier.

In this case there is actually a call like

  emit_modrm_dstoff(&prog, src_reg, dst_reg)

So calling the function args dst_reg, src_reg would be misleading.

I could call them ptr_reg and val_reg or something?

Re: [PATCH v2 bpf-next 01/13] bpf: x86: Factor out emission of ModR/M for *(reg + off)

[Alexei Starovoitov]

On Tue, Dec 1, 2020 at 4:14 AM Brendan Jackman <jackmanb@google.com> wrote:
>
> On Sat, Nov 28, 2020 at 05:15:52PM -0800, Alexei Starovoitov wrote:
> > On Fri, Nov 27, 2020 at 05:57:26PM +0000, Brendan Jackman wrote:
> > > +/* Emit the ModR/M byte for addressing *(r1 + off) and r2 */
> > > +static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off)
> >
> > same concern as in the another patch. If you could avoid intel's puzzling names
> > like above it will make reviewing the patch easier.
>
> In this case there is actually a call like
>
>   emit_modrm_dstoff(&prog, src_reg, dst_reg)

emit_insn_prefix() ?

Re: [PATCH v2 bpf-next 01/13] bpf: x86: Factor out emission of ModR/M for *(reg + off)

[Brendan Jackman]

Tue, Dec 01, 2020 at 09:50:00PM -0800, Alexei Starovoitov wrote:
> On Tue, Dec 1, 2020 at 4:14 AM Brendan Jackman <jackmanb@google.com> wrote:
> >
> > On Sat, Nov 28, 2020 at 05:15:52PM -0800, Alexei Starovoitov wrote:
> > > On Fri, Nov 27, 2020 at 05:57:26PM +0000, Brendan Jackman wrote:
> > > > +/* Emit the ModR/M byte for addressing *(r1 + off) and r2 */
> > > > +static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off)
> > >
> > > same concern as in the another patch. If you could avoid intel's puzzling names
> > > like above it will make reviewing the patch easier.
> >
> > In this case there is actually a call like
> >
> >   emit_modrm_dstoff(&prog, src_reg, dst_reg)
> 
> emit_insn_prefix() ?

Ah sorry, I thought you were talking about the _arg_ names.

This isn't a prefix, but emit_insn_suffix sounds good.

Re: [PATCH v2 bpf-next 01/13] bpf: x86: Factor out emission of ModR/M for *(reg + off)

[Alexei Starovoitov]

On Wed, Dec 2, 2020 at 2:52 AM Brendan Jackman <jackmanb@google.com> wrote:
>
> Tue, Dec 01, 2020 at 09:50:00PM -0800, Alexei Starovoitov wrote:
> > On Tue, Dec 1, 2020 at 4:14 AM Brendan Jackman <jackmanb@google.com> wrote:
> > >
> > > On Sat, Nov 28, 2020 at 05:15:52PM -0800, Alexei Starovoitov wrote:
> > > > On Fri, Nov 27, 2020 at 05:57:26PM +0000, Brendan Jackman wrote:
> > > > > +/* Emit the ModR/M byte for addressing *(r1 + off) and r2 */
> > > > > +static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off)
> > > >
> > > > same concern as in the another patch. If you could avoid intel's puzzling names
> > > > like above it will make reviewing the patch easier.
> > >
> > > In this case there is actually a call like
> > >
> > >   emit_modrm_dstoff(&prog, src_reg, dst_reg)
> >
> > emit_insn_prefix() ?
>
> Ah sorry, I thought you were talking about the _arg_ names.

I meant both. Arg names and helper name. Sorry for the confusion.

[PATCH v2 bpf-next 02/13] bpf: x86: Factor out emission of REX byte

[Brendan Jackman]

The JIT case for encoding atomic ops is about to get more
complicated. In order to make the review & resulting code easier,
let's factor out some shared helpers.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 arch/x86/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 94b17bd30e00..a839c1a54276 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -702,6 +702,21 @@ static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off)
 	*pprog = prog;
 }
 
+/*
+ * Emit a REX byte if it will be necessary to address these registers
+ */
+static void maybe_emit_rex(u8 **pprog, u32 reg_rm, u32 reg_reg, bool wide)
+{
+	u8 *prog = *pprog;
+	int cnt = 0;
+
+	if (wide)
+		EMIT1(add_2mod(0x48, reg_rm, reg_reg));
+	else if (is_ereg(reg_rm) || is_ereg(reg_reg))
+		EMIT1(add_2mod(0x40, reg_rm, reg_reg));
+	*pprog = prog;
+}
+
 /* LDX: dst_reg = *(u8*)(src_reg + off) */
 static void emit_ldx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
 {
@@ -854,10 +869,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			case BPF_OR: b2 = 0x09; break;
 			case BPF_XOR: b2 = 0x31; break;
 			}
-			if (BPF_CLASS(insn->code) == BPF_ALU64)
-				EMIT1(add_2mod(0x48, dst_reg, src_reg));
-			else if (is_ereg(dst_reg) || is_ereg(src_reg))
-				EMIT1(add_2mod(0x40, dst_reg, src_reg));
+			maybe_emit_rex(&prog, dst_reg, src_reg,
+				       BPF_CLASS(insn->code) == BPF_ALU64);
 			EMIT2(b2, add_2reg(0xC0, dst_reg, src_reg));
 			break;
 
@@ -1301,20 +1314,16 @@ xadd:			emit_modrm_dstoff(&prog, dst_reg, src_reg, insn->off);
 		case BPF_JMP32 | BPF_JSGE | BPF_X:
 		case BPF_JMP32 | BPF_JSLE | BPF_X:
 			/* cmp dst_reg, src_reg */
-			if (BPF_CLASS(insn->code) == BPF_JMP)
-				EMIT1(add_2mod(0x48, dst_reg, src_reg));
-			else if (is_ereg(dst_reg) || is_ereg(src_reg))
-				EMIT1(add_2mod(0x40, dst_reg, src_reg));
+			maybe_emit_rex(&prog, dst_reg, src_reg,
+				       BPF_CLASS(insn->code) == BPF_JMP);
 			EMIT2(0x39, add_2reg(0xC0, dst_reg, src_reg));
 			goto emit_cond_jmp;
 
 		case BPF_JMP | BPF_JSET | BPF_X:
 		case BPF_JMP32 | BPF_JSET | BPF_X:
 			/* test dst_reg, src_reg */
-			if (BPF_CLASS(insn->code) == BPF_JMP)
-				EMIT1(add_2mod(0x48, dst_reg, src_reg));
-			else if (is_ereg(dst_reg) || is_ereg(src_reg))
-				EMIT1(add_2mod(0x40, dst_reg, src_reg));
+			maybe_emit_rex(&prog, dst_reg, src_reg,
+				       BPF_CLASS(insn->code) == BPF_JMP);
 			EMIT2(0x85, add_2reg(0xC0, dst_reg, src_reg));
 			goto emit_cond_jmp;
 
@@ -1350,10 +1359,8 @@ xadd:			emit_modrm_dstoff(&prog, dst_reg, src_reg, insn->off);
 		case BPF_JMP32 | BPF_JSLE | BPF_K:
 			/* test dst_reg, dst_reg to save one extra byte */
 			if (imm32 == 0) {
-				if (BPF_CLASS(insn->code) == BPF_JMP)
-					EMIT1(add_2mod(0x48, dst_reg, dst_reg));
-				else if (is_ereg(dst_reg))
-					EMIT1(add_2mod(0x40, dst_reg, dst_reg));
+				maybe_emit_rex(&prog, dst_reg, dst_reg,
+					       BPF_CLASS(insn->code) == BPF_JMP);
 				EMIT2(0x85, add_2reg(0xC0, dst_reg, dst_reg));
 				goto emit_cond_jmp;
 			}
-- 
2.29.2.454.gaff20da3a2-goog

Re: [PATCH v2 bpf-next 02/13] bpf: x86: Factor out emission of REX byte

[Alexei Starovoitov]

On Fri, Nov 27, 2020 at 05:57:27PM +0000, Brendan Jackman wrote:
> The JIT case for encoding atomic ops is about to get more
> complicated. In order to make the review & resulting code easier,
> let's factor out some shared helpers.
> 
> Signed-off-by: Brendan Jackman <jackmanb@google.com>
> ---
>  arch/x86/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++---------------
>  1 file changed, 23 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 94b17bd30e00..a839c1a54276 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -702,6 +702,21 @@ static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off)
>  	*pprog = prog;
>  }
>  
> +/*
> + * Emit a REX byte if it will be necessary to address these registers

What is "REX byte" ?
May be rename it to maybe_emit_mod() ?

> + */
> +static void maybe_emit_rex(u8 **pprog, u32 reg_rm, u32 reg_reg, bool wide)

could you please keep original names as dst_reg/src_reg instead of reg_rm/reg_reg ?
reg_reg reads really odd and reg_rm is equally puzzling unless the reader studied
intel's manual. I didn't. All these new abbreviations are challenging for me.
> +{
> +	u8 *prog = *pprog;
> +	int cnt = 0;
> +
> +	if (wide)

what is 'wide' ? Why not to call it 'bool is_alu64' ?

> +		EMIT1(add_2mod(0x48, reg_rm, reg_reg));
> +	else if (is_ereg(reg_rm) || is_ereg(reg_reg))
> +		EMIT1(add_2mod(0x40, reg_rm, reg_reg));
> +	*pprog = prog;
> +}

Re: [PATCH v2 bpf-next 02/13] bpf: x86: Factor out emission of REX byte

[Brendan Jackman]

On Sat, Nov 28, 2020 at 05:14:05PM -0800, Alexei Starovoitov wrote:
> On Fri, Nov 27, 2020 at 05:57:27PM +0000, Brendan Jackman wrote:
> > The JIT case for encoding atomic ops is about to get more
> > complicated. In order to make the review & resulting code easier,
> > let's factor out some shared helpers.
> > 
> > Signed-off-by: Brendan Jackman <jackmanb@google.com>
> > ---
> >  arch/x86/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++---------------
> >  1 file changed, 23 insertions(+), 16 deletions(-)
> > 
> > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> > index 94b17bd30e00..a839c1a54276 100644
> > --- a/arch/x86/net/bpf_jit_comp.c
> > +++ b/arch/x86/net/bpf_jit_comp.c
> > @@ -702,6 +702,21 @@ static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off)
> >  	*pprog = prog;
> >  }
> >  
> > +/*
> > + * Emit a REX byte if it will be necessary to address these registers
> 
> What is "REX byte" ?
> May be rename it to maybe_emit_mod() ?

Er, this is the REX prefix as described in
https://wiki.osdev.org/X86-64_Instruction_Encoding#REX_prefix

Would maybe_emit_mod be accurate? In my mind "mod" is a field in the
ModR/M byte which comes _after_ the opcode. Before developing this
patchset I knew almost nothing about x86, so maybe I'm missing something
about the general terminology?

> > + */
> > +static void maybe_emit_rex(u8 **pprog, u32 reg_rm, u32 reg_reg, bool wide)
> 
> could you please keep original names as dst_reg/src_reg instead of reg_rm/reg_reg ?
> reg_reg reads really odd and reg_rm is equally puzzling unless the reader studied
> intel's manual. I didn't. All these new abbreviations are challenging for me.

OK. I originally changed it to use the x86 names because in theory you
could do:

  maybe_emit_rex(&prog, src_reg, dst_reg);

so the names would look backwards when you jump into the function
implementation.

> > +{
> > +	u8 *prog = *pprog;
> > +	int cnt = 0;
> > +
> > +	if (wide)
> 
> what is 'wide' ? Why not to call it 'bool is_alu64' ?

Ack - there's precedent in the file for 'is64' so I'll go with that.

Re: [PATCH v2 bpf-next 02/13] bpf: x86: Factor out emission of REX byte

[Alexei Starovoitov]

On Tue, Dec 1, 2020 at 4:12 AM Brendan Jackman <jackmanb@google.com> wrote:
>
> On Sat, Nov 28, 2020 at 05:14:05PM -0800, Alexei Starovoitov wrote:
> > On Fri, Nov 27, 2020 at 05:57:27PM +0000, Brendan Jackman wrote:
> > > The JIT case for encoding atomic ops is about to get more
> > > complicated. In order to make the review & resulting code easier,
> > > let's factor out some shared helpers.
> > >
> > > Signed-off-by: Brendan Jackman <jackmanb@google.com>
> > > ---
> > >  arch/x86/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++---------------
> > >  1 file changed, 23 insertions(+), 16 deletions(-)
> > >
> > > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> > > index 94b17bd30e00..a839c1a54276 100644
> > > --- a/arch/x86/net/bpf_jit_comp.c
> > > +++ b/arch/x86/net/bpf_jit_comp.c
> > > @@ -702,6 +702,21 @@ static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off)
> > >     *pprog = prog;
> > >  }
> > >
> > > +/*
> > > + * Emit a REX byte if it will be necessary to address these registers
> >
> > What is "REX byte" ?
> > May be rename it to maybe_emit_mod() ?
>
> Er, this is the REX prefix as described in
> https://wiki.osdev.org/X86-64_Instruction_Encoding#REX_prefix
>
> Would maybe_emit_mod be accurate? In my mind "mod" is a field in the
> ModR/M byte which comes _after_ the opcode. Before developing this
> patchset I knew almost nothing about x86, so maybe I'm missing something
> about the general terminology?

I wrote the JIT without looking into the manual and without studying
the terminology.
Why? Because it was not necessary. I still don't see a reason why
that obscure terminology needs to be brought in into the code.
'mod' to me is a 'modifier'. Nothing to do with intel's modrm thing.

Re: [PATCH v2 bpf-next 02/13] bpf: x86: Factor out emission of REX byte

[Brendan Jackman]

On Tue, Dec 01, 2020 at 09:48:36PM -0800, Alexei Starovoitov wrote:
> On Tue, Dec 1, 2020 at 4:12 AM Brendan Jackman <jackmanb@google.com> wrote:
> >
> > On Sat, Nov 28, 2020 at 05:14:05PM -0800, Alexei Starovoitov wrote:
> > > On Fri, Nov 27, 2020 at 05:57:27PM +0000, Brendan Jackman wrote:
> > > > The JIT case for encoding atomic ops is about to get more
> > > > complicated. In order to make the review & resulting code easier,
> > > > let's factor out some shared helpers.
> > > >
> > > > Signed-off-by: Brendan Jackman <jackmanb@google.com>
> > > > ---
> > > >  arch/x86/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++---------------
> > > >  1 file changed, 23 insertions(+), 16 deletions(-)
> > > >
> > > > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> > > > index 94b17bd30e00..a839c1a54276 100644
> > > > --- a/arch/x86/net/bpf_jit_comp.c
> > > > +++ b/arch/x86/net/bpf_jit_comp.c
> > > > @@ -702,6 +702,21 @@ static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off)
> > > >     *pprog = prog;
> > > >  }
> > > >
> > > > +/*
> > > > + * Emit a REX byte if it will be necessary to address these registers
> > >
> > > What is "REX byte" ?
> > > May be rename it to maybe_emit_mod() ?
> >
> > Er, this is the REX prefix as described in
> > https://wiki.osdev.org/X86-64_Instruction_Encoding#REX_prefix
> >
> > Would maybe_emit_mod be accurate? In my mind "mod" is a field in the
> > ModR/M byte which comes _after_ the opcode. Before developing this
> > patchset I knew almost nothing about x86, so maybe I'm missing something
> > about the general terminology?
> 
> I wrote the JIT without looking into the manual and without studying
> the terminology.
> Why? Because it was not necessary. I still don't see a reason why
> that obscure terminology needs to be brought in into the code.
> 'mod' to me is a 'modifier'. Nothing to do with intel's modrm thing.

OK, calling it maybe_emit_mod(pprog, dst_reg, src_reg)

[PATCH v2 bpf-next 03/13] bpf: x86: Factor out function to emit NEG

[Brendan Jackman]

There's currently only one usage of this but implementation of
atomic_sub add another.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 arch/x86/net/bpf_jit_comp.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index a839c1a54276..49dea0c1a130 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -783,6 +783,22 @@ static void emit_stx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
 	*pprog = prog;
 }
 
+
+static void emit_neg(u8 **pprog, u32 reg, bool is64)
+{
+	u8 *prog = *pprog;
+	int cnt = 0;
+
+	/* Emit REX byte if necessary */
+	if (is64)
+		EMIT1(add_1mod(0x48, reg));
+	else if (is_ereg(reg))
+		EMIT1(add_1mod(0x40, reg));
+
+	EMIT2(0xF7, add_1reg(0xD8, reg)); /* x86 NEG */
+	*pprog = prog;
+}
+
 static bool ex_handler_bpf(const struct exception_table_entry *x,
 			   struct pt_regs *regs, int trapnr,
 			   unsigned long error_code, unsigned long fault_addr)
@@ -884,11 +900,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			/* neg dst */
 		case BPF_ALU | BPF_NEG:
 		case BPF_ALU64 | BPF_NEG:
-			if (BPF_CLASS(insn->code) == BPF_ALU64)
-				EMIT1(add_1mod(0x48, dst_reg));
-			else if (is_ereg(dst_reg))
-				EMIT1(add_1mod(0x40, dst_reg));
-			EMIT2(0xF7, add_1reg(0xD8, dst_reg));
+			emit_neg(&prog, dst_reg,
+				 BPF_CLASS(insn->code) == BPF_ALU64);
 			break;
 
 		case BPF_ALU | BPF_ADD | BPF_K:
-- 
2.29.2.454.gaff20da3a2-goog

[PATCH v2 bpf-next 04/13] bpf: x86: Factor out a lookup table for some ALU opcodes

[Brendan Jackman]

A later commit will need to lookup a subset of these opcodes. To
avoid duplicating code, pull out a table.

The shift opcodes won't be needed by that later commit, but they're
already duplicated, so fold them into the table anyway.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 arch/x86/net/bpf_jit_comp.c | 33 +++++++++++++++------------------
 1 file changed, 15 insertions(+), 18 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 49dea0c1a130..9ecee9d018ac 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -205,6 +205,18 @@ static u8 add_2reg(u8 byte, u32 dst_reg, u32 src_reg)
 	return byte + reg2hex[dst_reg] + (reg2hex[src_reg] << 3);
 }
 
+/* Some 1-byte opcodes for binary ALU operations */
+static u8 simple_alu_opcodes[] = {
+	[BPF_ADD] = 0x01,
+	[BPF_SUB] = 0x29,
+	[BPF_AND] = 0x21,
+	[BPF_OR] = 0x09,
+	[BPF_XOR] = 0x31,
+	[BPF_LSH] = 0xE0,
+	[BPF_RSH] = 0xE8,
+	[BPF_ARSH] = 0xF8,
+};
+
 static void jit_fill_hole(void *area, unsigned int size)
 {
 	/* Fill whole space with INT3 instructions */
@@ -878,15 +890,9 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 		case BPF_ALU64 | BPF_AND | BPF_X:
 		case BPF_ALU64 | BPF_OR | BPF_X:
 		case BPF_ALU64 | BPF_XOR | BPF_X:
-			switch (BPF_OP(insn->code)) {
-			case BPF_ADD: b2 = 0x01; break;
-			case BPF_SUB: b2 = 0x29; break;
-			case BPF_AND: b2 = 0x21; break;
-			case BPF_OR: b2 = 0x09; break;
-			case BPF_XOR: b2 = 0x31; break;
-			}
 			maybe_emit_rex(&prog, dst_reg, src_reg,
 				       BPF_CLASS(insn->code) == BPF_ALU64);
+			b2 = simple_alu_opcodes[BPF_OP(insn->code)];
 			EMIT2(b2, add_2reg(0xC0, dst_reg, src_reg));
 			break;
 
@@ -1063,12 +1069,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			else if (is_ereg(dst_reg))
 				EMIT1(add_1mod(0x40, dst_reg));
 
-			switch (BPF_OP(insn->code)) {
-			case BPF_LSH: b3 = 0xE0; break;
-			case BPF_RSH: b3 = 0xE8; break;
-			case BPF_ARSH: b3 = 0xF8; break;
-			}
-
+			b3 = simple_alu_opcodes[BPF_OP(insn->code)];
 			if (imm32 == 1)
 				EMIT2(0xD1, add_1reg(b3, dst_reg));
 			else
@@ -1102,11 +1103,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			else if (is_ereg(dst_reg))
 				EMIT1(add_1mod(0x40, dst_reg));
 
-			switch (BPF_OP(insn->code)) {
-			case BPF_LSH: b3 = 0xE0; break;
-			case BPF_RSH: b3 = 0xE8; break;
-			case BPF_ARSH: b3 = 0xF8; break;
-			}
+			b3 = simple_alu_opcodes[BPF_OP(insn->code)];
 			EMIT2(0xD3, add_1reg(b3, dst_reg));
 
 			if (src_reg != BPF_REG_4)
-- 
2.29.2.454.gaff20da3a2-goog

[PATCH v2 bpf-next 05/13] bpf: Rename BPF_XADD and prepare to encode other atomics in .imm

[Brendan Jackman]

A subsequent patch will add additional atomic operations. These new
operations will use the same opcode field as the existing XADD, with
the immediate discriminating different operations.

In preparation, rename the instruction mode BPF_ATOMIC and start
calling the zero immediate BPF_ADD.

This is possible (doesn't break existing valid BPF progs) because the
immediate field is currently reserved MBZ and BPF_ADD is zero.

All uses are removed from the tree but the BPF_XADD definition is
kept around to avoid breaking builds for people including kernel
headers.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 Documentation/networking/filter.rst           | 30 +++++++-----
 arch/arm/net/bpf_jit_32.c                     |  7 ++-
 arch/arm64/net/bpf_jit_comp.c                 | 16 +++++--
 arch/mips/net/ebpf_jit.c                      | 11 +++--
 arch/powerpc/net/bpf_jit_comp64.c             | 25 ++++++++--
 arch/riscv/net/bpf_jit_comp32.c               | 20 ++++++--
 arch/riscv/net/bpf_jit_comp64.c               | 16 +++++--
 arch/s390/net/bpf_jit_comp.c                  | 27 ++++++-----
 arch/sparc/net/bpf_jit_comp_64.c              | 17 +++++--
 arch/x86/net/bpf_jit_comp.c                   | 46 ++++++++++++++-----
 arch/x86/net/bpf_jit_comp32.c                 |  6 +--
 drivers/net/ethernet/netronome/nfp/bpf/jit.c  | 14 ++++--
 drivers/net/ethernet/netronome/nfp/bpf/main.h |  4 +-
 .../net/ethernet/netronome/nfp/bpf/verifier.c | 15 ++++--
 include/linux/filter.h                        |  8 ++--
 include/uapi/linux/bpf.h                      |  3 +-
 kernel/bpf/core.c                             | 31 +++++++++----
 kernel/bpf/disasm.c                           |  6 ++-
 kernel/bpf/verifier.c                         | 24 ++++++----
 lib/test_bpf.c                                |  2 +-
 samples/bpf/bpf_insn.h                        |  4 +-
 samples/bpf/sock_example.c                    |  2 +-
 samples/bpf/test_cgrp2_attach.c               |  4 +-
 tools/include/linux/filter.h                  |  7 +--
 tools/include/uapi/linux/bpf.h                |  3 +-
 .../bpf/prog_tests/cgroup_attach_multi.c      |  4 +-
 tools/testing/selftests/bpf/verifier/ctx.c    |  7 ++-
 .../testing/selftests/bpf/verifier/leak_ptr.c |  4 +-
 tools/testing/selftests/bpf/verifier/unpriv.c |  3 +-
 tools/testing/selftests/bpf/verifier/xadd.c   |  2 +-
 30 files changed, 248 insertions(+), 120 deletions(-)

diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst
index debb59e374de..1583d59d806d 100644
--- a/Documentation/networking/filter.rst
+++ b/Documentation/networking/filter.rst
@@ -1006,13 +1006,13 @@ Size modifier is one of ...
 
 Mode modifier is one of::
 
-  BPF_IMM  0x00  /* used for 32-bit mov in classic BPF and 64-bit in eBPF */
-  BPF_ABS  0x20
-  BPF_IND  0x40
-  BPF_MEM  0x60
-  BPF_LEN  0x80  /* classic BPF only, reserved in eBPF */
-  BPF_MSH  0xa0  /* classic BPF only, reserved in eBPF */
-  BPF_XADD 0xc0  /* eBPF only, exclusive add */
+  BPF_IMM     0x00  /* used for 32-bit mov in classic BPF and 64-bit in eBPF */
+  BPF_ABS     0x20
+  BPF_IND     0x40
+  BPF_MEM     0x60
+  BPF_LEN     0x80  /* classic BPF only, reserved in eBPF */
+  BPF_MSH     0xa0  /* classic BPF only, reserved in eBPF */
+  BPF_ATOMIC  0xc0  /* eBPF only, atomic operations */
 
 eBPF has two non-generic instructions: (BPF_ABS | <size> | BPF_LD) and
 (BPF_IND | <size> | BPF_LD) which are used to access packet data.
@@ -1044,11 +1044,19 @@ Unlike classic BPF instruction set, eBPF has generic load/store operations::
     BPF_MEM | <size> | BPF_STX:  *(size *) (dst_reg + off) = src_reg
     BPF_MEM | <size> | BPF_ST:   *(size *) (dst_reg + off) = imm32
     BPF_MEM | <size> | BPF_LDX:  dst_reg = *(size *) (src_reg + off)
-    BPF_XADD | BPF_W  | BPF_STX: lock xadd *(u32 *)(dst_reg + off16) += src_reg
-    BPF_XADD | BPF_DW | BPF_STX: lock xadd *(u64 *)(dst_reg + off16) += src_reg
 
-Where size is one of: BPF_B or BPF_H or BPF_W or BPF_DW. Note that 1 and
-2 byte atomic increments are not supported.
+Where size is one of: BPF_B or BPF_H or BPF_W or BPF_DW.
+
+It also includes atomic operations, which use the immediate field for extra
+encoding.
+
+   .imm = BPF_ADD, .code = BPF_ATOMIC | BPF_W  | BPF_STX: lock xadd *(u32 *)(dst_reg + off16) += src_reg
+   .imm = BPF_ADD, .code = BPF_ATOMIC | BPF_DW | BPF_STX: lock xadd *(u64 *)(dst_reg + off16) += src_reg
+
+Note that 1 and 2 byte atomic operations are not supported.
+
+You may encounter BPF_XADD - this is a legacy name for BPF_ATOMIC, referring to
+the exclusive-add operation encoded when the immediate field is zero.
 
 eBPF has one 16-byte instruction: BPF_LD | BPF_DW | BPF_IMM which consists
 of two consecutive ``struct bpf_insn`` 8-byte blocks and interpreted as single
diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
index 0207b6ea6e8a..897634d0a67c 100644
--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -1620,10 +1620,9 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
 		}
 		emit_str_r(dst_lo, tmp2, off, ctx, BPF_SIZE(code));
 		break;
-	/* STX XADD: lock *(u32 *)(dst + off) += src */
-	case BPF_STX | BPF_XADD | BPF_W:
-	/* STX XADD: lock *(u64 *)(dst + off) += src */
-	case BPF_STX | BPF_XADD | BPF_DW:
+	/* Atomic ops */
+	case BPF_STX | BPF_ATOMIC | BPF_W:
+	case BPF_STX | BPF_ATOMIC | BPF_DW:
 		goto notyet;
 	/* STX: *(size *)(dst + off) = src */
 	case BPF_STX | BPF_MEM | BPF_W:
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index ef9f1d5e989d..f7b194878a99 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -875,10 +875,18 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 		}
 		break;
 
-	/* STX XADD: lock *(u32 *)(dst + off) += src */
-	case BPF_STX | BPF_XADD | BPF_W:
-	/* STX XADD: lock *(u64 *)(dst + off) += src */
-	case BPF_STX | BPF_XADD | BPF_DW:
+	case BPF_STX | BPF_ATOMIC | BPF_W:
+	case BPF_STX | BPF_ATOMIC | BPF_DW:
+		if (insn->imm != BPF_ADD) {
+			pr_err_once("unknown atomic op code %02x\n", insn->imm);
+			return -EINVAL;
+		}
+
+		/* STX XADD: lock *(u32 *)(dst + off) += src
+		 * and
+		 * STX XADD: lock *(u64 *)(dst + off) += src
+		 */
+
 		if (!off) {
 			reg = dst;
 		} else {
diff --git a/arch/mips/net/ebpf_jit.c b/arch/mips/net/ebpf_jit.c
index 561154cbcc40..939dd06764bc 100644
--- a/arch/mips/net/ebpf_jit.c
+++ b/arch/mips/net/ebpf_jit.c
@@ -1423,8 +1423,8 @@ static int build_one_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 	case BPF_STX | BPF_H | BPF_MEM:
 	case BPF_STX | BPF_W | BPF_MEM:
 	case BPF_STX | BPF_DW | BPF_MEM:
-	case BPF_STX | BPF_W | BPF_XADD:
-	case BPF_STX | BPF_DW | BPF_XADD:
+	case BPF_STX | BPF_W | BPF_ATOMIC:
+	case BPF_STX | BPF_DW | BPF_ATOMIC:
 		if (insn->dst_reg == BPF_REG_10) {
 			ctx->flags |= EBPF_SEEN_FP;
 			dst = MIPS_R_SP;
@@ -1438,7 +1438,12 @@ static int build_one_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 		src = ebpf_to_mips_reg(ctx, insn, src_reg_no_fp);
 		if (src < 0)
 			return src;
-		if (BPF_MODE(insn->code) == BPF_XADD) {
+		if (BPF_MODE(insn->code) == BPF_ATOMIC) {
+			if (insn->imm != BPF_ADD) {
+				pr_err("ATOMIC OP %02x NOT HANDLED\n", insn->imm);
+				return -EINVAL;
+			}
+
 			/*
 			 * If mem_off does not fit within the 9 bit ll/sc
 			 * instruction immediate field, use a temp reg.
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 022103c6a201..aaf1a887f653 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -683,10 +683,18 @@ static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
 			break;
 
 		/*
-		 * BPF_STX XADD (atomic_add)
+		 * BPF_STX ATOMIC (atomic ops)
 		 */
-		/* *(u32 *)(dst + off) += src */
-		case BPF_STX | BPF_XADD | BPF_W:
+		case BPF_STX | BPF_ATOMIC | BPF_W:
+			if (insn->imm != BPF_ADD) {
+				pr_err_ratelimited(
+					"eBPF filter atomic op code %02x (@%d) unsupported\n",
+					code, i);
+				return -ENOTSUPP;
+			}
+
+			/* *(u32 *)(dst + off) += src */
+
 			/* Get EA into TMP_REG_1 */
 			EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], dst_reg, off));
 			tmp_idx = ctx->idx * 4;
@@ -699,8 +707,15 @@ static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
 			/* we're done if this succeeded */
 			PPC_BCC_SHORT(COND_NE, tmp_idx);
 			break;
-		/* *(u64 *)(dst + off) += src */
-		case BPF_STX | BPF_XADD | BPF_DW:
+		case BPF_STX | BPF_ATOMIC | BPF_DW:
+			if (insn->imm != BPF_ADD) {
+				pr_err_ratelimited(
+					"eBPF filter atomic op code %02x (@%d) unsupported\n",
+					code, i);
+				return -ENOTSUPP;
+			}
+			/* *(u64 *)(dst + off) += src */
+
 			EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], dst_reg, off));
 			tmp_idx = ctx->idx * 4;
 			EMIT(PPC_RAW_LDARX(b2p[TMP_REG_2], 0, b2p[TMP_REG_1], 0));
diff --git a/arch/riscv/net/bpf_jit_comp32.c b/arch/riscv/net/bpf_jit_comp32.c
index 579575f9cdae..a9ef808b235f 100644
--- a/arch/riscv/net/bpf_jit_comp32.c
+++ b/arch/riscv/net/bpf_jit_comp32.c
@@ -881,7 +881,7 @@ static int emit_store_r64(const s8 *dst, const s8 *src, s16 off,
 	const s8 *rd = bpf_get_reg64(dst, tmp1, ctx);
 	const s8 *rs = bpf_get_reg64(src, tmp2, ctx);
 
-	if (mode == BPF_XADD && size != BPF_W)
+	if (mode == BPF_ATOMIC && (size != BPF_W || imm != BPF_ADD))
 		return -1;
 
 	emit_imm(RV_REG_T0, off, ctx);
@@ -899,7 +899,7 @@ static int emit_store_r64(const s8 *dst, const s8 *src, s16 off,
 		case BPF_MEM:
 			emit(rv_sw(RV_REG_T0, 0, lo(rs)), ctx);
 			break;
-		case BPF_XADD:
+		case BPF_ATOMIC: /* .imm checked above - only BPF_ADD allowed */
 			emit(rv_amoadd_w(RV_REG_ZERO, lo(rs), RV_REG_T0, 0, 0),
 			     ctx);
 			break;
@@ -1260,7 +1260,6 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 	case BPF_STX | BPF_MEM | BPF_H:
 	case BPF_STX | BPF_MEM | BPF_W:
 	case BPF_STX | BPF_MEM | BPF_DW:
-	case BPF_STX | BPF_XADD | BPF_W:
 		if (BPF_CLASS(code) == BPF_ST) {
 			emit_imm32(tmp2, imm, ctx);
 			src = tmp2;
@@ -1271,8 +1270,21 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 			return -1;
 		break;
 
+	case BPF_STX | BPF_ATOMIC | BPF_W:
+		if (insn->imm != BPF_ADD) {
+			pr_info_once(
+				"bpf-jit: not supported: atomic operation %02x ***\n",
+				insn->imm);
+			return -EFAULT;
+		}
+
+		if (emit_store_r64(dst, src, off, ctx, BPF_SIZE(code),
+				   BPF_MODE(code)))
+			return -1;
+		break;
+
 	/* No hardware support for 8-byte atomics in RV32. */
-	case BPF_STX | BPF_XADD | BPF_DW:
+	case BPF_STX | BPF_ATOMIC | BPF_DW:
 		/* Fallthrough. */
 
 notsupported:
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index 8a56b5293117..b44ff52f84a6 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -1027,10 +1027,18 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 		emit_add(RV_REG_T1, RV_REG_T1, rd, ctx);
 		emit_sd(RV_REG_T1, 0, rs, ctx);
 		break;
-	/* STX XADD: lock *(u32 *)(dst + off) += src */
-	case BPF_STX | BPF_XADD | BPF_W:
-	/* STX XADD: lock *(u64 *)(dst + off) += src */
-	case BPF_STX | BPF_XADD | BPF_DW:
+	case BPF_STX | BPF_ATOMIC | BPF_W:
+	case BPF_STX | BPF_ATOMIC | BPF_DW:
+		if (insn->imm != BPF_ADD) {
+			pr_err("bpf-jit: not supported: atomic operation %02x ***\n",
+			       insn->imm);
+			return -EINVAL;
+		}
+
+		/* atomic_add: lock *(u32 *)(dst + off) += src
+		 * atomic_add: lock *(u64 *)(dst + off) += src
+		 */
+
 		if (off) {
 			if (is_12b_int(off)) {
 				emit_addi(RV_REG_T1, rd, off, ctx);
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 0a4182792876..f973e2ead197 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -1205,18 +1205,23 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
 		jit->seen |= SEEN_MEM;
 		break;
 	/*
-	 * BPF_STX XADD (atomic_add)
+	 * BPF_ATOMIC
 	 */
-	case BPF_STX | BPF_XADD | BPF_W: /* *(u32 *)(dst + off) += src */
-		/* laal %w0,%src,off(%dst) */
-		EMIT6_DISP_LH(0xeb000000, 0x00fa, REG_W0, src_reg,
-			      dst_reg, off);
-		jit->seen |= SEEN_MEM;
-		break;
-	case BPF_STX | BPF_XADD | BPF_DW: /* *(u64 *)(dst + off) += src */
-		/* laalg %w0,%src,off(%dst) */
-		EMIT6_DISP_LH(0xeb000000, 0x00ea, REG_W0, src_reg,
-			      dst_reg, off);
+	case BPF_STX | BPF_ATOMIC | BPF_DW:
+	case BPF_STX | BPF_ATOMIC | BPF_W:
+		if (insn->imm != BPF_ADD) {
+			pr_err("Unknown atomic operation %02x\n", insn->imm);
+			return -1;
+		}
+
+		/* *(u32/u64 *)(dst + off) += src
+		 *
+		 * BFW_W:  laal  %w0,%src,off(%dst)
+		 * BPF_DW: laalg %w0,%src,off(%dst)
+		 */
+		EMIT6_DISP_LH(0xeb000000,
+			      BPF_SIZE(insn->code) == BPF_W ? 0x00fa : 0x00ea,
+			      REG_W0, src_reg, dst_reg, off);
 		jit->seen |= SEEN_MEM;
 		break;
 	/*
diff --git a/arch/sparc/net/bpf_jit_comp_64.c b/arch/sparc/net/bpf_jit_comp_64.c
index 3364e2a00989..4b8d3c65d266 100644
--- a/arch/sparc/net/bpf_jit_comp_64.c
+++ b/arch/sparc/net/bpf_jit_comp_64.c
@@ -1366,12 +1366,18 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
 		break;
 	}
 
-	/* STX XADD: lock *(u32 *)(dst + off) += src */
-	case BPF_STX | BPF_XADD | BPF_W: {
+	case BPF_STX | BPF_ATOMIC | BPF_W: {
 		const u8 tmp = bpf2sparc[TMP_REG_1];
 		const u8 tmp2 = bpf2sparc[TMP_REG_2];
 		const u8 tmp3 = bpf2sparc[TMP_REG_3];
 
+		if (insn->imm != BPF_ADD) {
+			pr_err_once("unknown atomic op %02x\n", insn->imm);
+			return -EINVAL;
+		}
+
+		/* lock *(u32 *)(dst + off) += src */
+
 		if (insn->dst_reg == BPF_REG_FP)
 			ctx->saw_frame_pointer = true;
 
@@ -1390,11 +1396,16 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
 		break;
 	}
 	/* STX XADD: lock *(u64 *)(dst + off) += src */
-	case BPF_STX | BPF_XADD | BPF_DW: {
+	case BPF_STX | BPF_ATOMIC | BPF_DW: {
 		const u8 tmp = bpf2sparc[TMP_REG_1];
 		const u8 tmp2 = bpf2sparc[TMP_REG_2];
 		const u8 tmp3 = bpf2sparc[TMP_REG_3];
 
+		if (insn->imm != BPF_ADD) {
+			pr_err_once("unknown atomic op %02x\n", insn->imm);
+			return -EINVAL;
+		}
+
 		if (insn->dst_reg == BPF_REG_FP)
 			ctx->saw_frame_pointer = true;
 
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 9ecee9d018ac..7c47ad70ddb4 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -811,6 +811,34 @@ static void emit_neg(u8 **pprog, u32 reg, bool is64)
 	*pprog = prog;
 }
 
+static int emit_atomic(u8 **pprog, u8 atomic_op,
+		       u32 dst_reg, u32 src_reg, s16 off, u8 bpf_size)
+{
+	u8 *prog = *pprog;
+	int cnt = 0;
+
+	EMIT1(0xF0); /* lock prefix */
+
+	maybe_emit_rex(&prog, dst_reg, src_reg, bpf_size == BPF_DW);
+
+	/* emit opcode */
+	switch (atomic_op) {
+	case BPF_ADD:
+		/* lock *(u32/u64*)(dst_reg + off) <op>= src_reg */
+		EMIT1(simple_alu_opcodes[atomic_op]);
+		break;
+	default:
+		pr_err("bpf_jit: unknown atomic opcode %02x\n", atomic_op);
+		return -EFAULT;
+	}
+
+	emit_modrm_dstoff(&prog, dst_reg, src_reg, off);
+
+	*pprog = prog;
+	return 0;
+}
+
+
 static bool ex_handler_bpf(const struct exception_table_entry *x,
 			   struct pt_regs *regs, int trapnr,
 			   unsigned long error_code, unsigned long fault_addr)
@@ -855,6 +883,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 	int i, cnt = 0, excnt = 0;
 	int proglen = 0;
 	u8 *prog = temp;
+	int err;
 
 	detect_reg_usage(insn, insn_cnt, callee_regs_used,
 			 &tail_call_seen);
@@ -1263,17 +1292,12 @@ st:			if (is_imm8(insn->off))
 			}
 			break;
 
-			/* STX XADD: lock *(u32*)(dst_reg + off) += src_reg */
-		case BPF_STX | BPF_XADD | BPF_W:
-			/* Emit 'lock add dword ptr [rax + off], eax' */
-			if (is_ereg(dst_reg) || is_ereg(src_reg))
-				EMIT3(0xF0, add_2mod(0x40, dst_reg, src_reg), 0x01);
-			else
-				EMIT2(0xF0, 0x01);
-			goto xadd;
-		case BPF_STX | BPF_XADD | BPF_DW:
-			EMIT3(0xF0, add_2mod(0x48, dst_reg, src_reg), 0x01);
-xadd:			emit_modrm_dstoff(&prog, dst_reg, src_reg, insn->off);
+		case BPF_STX | BPF_ATOMIC | BPF_W:
+		case BPF_STX | BPF_ATOMIC | BPF_DW:
+			err = emit_atomic(&prog, insn->imm, dst_reg, src_reg,
+					  insn->off, BPF_SIZE(insn->code));
+			if (err)
+				return err;
 			break;
 
 			/* call */
diff --git a/arch/x86/net/bpf_jit_comp32.c b/arch/x86/net/bpf_jit_comp32.c
index 96fde03aa987..d17b67c69f89 100644
--- a/arch/x86/net/bpf_jit_comp32.c
+++ b/arch/x86/net/bpf_jit_comp32.c
@@ -2243,10 +2243,8 @@ emit_cond_jmp:		jmp_cond = get_cond_jmp_opcode(BPF_OP(code), false);
 				return -EFAULT;
 			}
 			break;
-		/* STX XADD: lock *(u32 *)(dst + off) += src */
-		case BPF_STX | BPF_XADD | BPF_W:
-		/* STX XADD: lock *(u64 *)(dst + off) += src */
-		case BPF_STX | BPF_XADD | BPF_DW:
+		case BPF_STX | BPF_ATOMIC | BPF_W:
+		case BPF_STX | BPF_ATOMIC | BPF_DW:
 			goto notyet;
 		case BPF_JMP | BPF_EXIT:
 			if (seen_exit) {
diff --git a/drivers/net/ethernet/netronome/nfp/bpf/jit.c b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
index 0a721f6e8676..1c9efc74edfc 100644
--- a/drivers/net/ethernet/netronome/nfp/bpf/jit.c
+++ b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
@@ -3109,13 +3109,19 @@ mem_xadd(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta, bool is64)
 	return 0;
 }
 
-static int mem_xadd4(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
+static int mem_atomic4(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
 {
+	if (meta->insn.off != BPF_ADD)
+		return -EOPNOTSUPP;
+
 	return mem_xadd(nfp_prog, meta, false);
 }
 
-static int mem_xadd8(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
+static int mem_atomic8(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
 {
+	if (meta->insn.off != BPF_ADD)
+		return -EOPNOTSUPP;
+
 	return mem_xadd(nfp_prog, meta, true);
 }
 
@@ -3475,8 +3481,8 @@ static const instr_cb_t instr_cb[256] = {
 	[BPF_STX | BPF_MEM | BPF_H] =	mem_stx2,
 	[BPF_STX | BPF_MEM | BPF_W] =	mem_stx4,
 	[BPF_STX | BPF_MEM | BPF_DW] =	mem_stx8,
-	[BPF_STX | BPF_XADD | BPF_W] =	mem_xadd4,
-	[BPF_STX | BPF_XADD | BPF_DW] =	mem_xadd8,
+	[BPF_STX | BPF_ATOMIC | BPF_W] =	mem_atomic4,
+	[BPF_STX | BPF_ATOMIC | BPF_DW] =	mem_atomic8,
 	[BPF_ST | BPF_MEM | BPF_B] =	mem_st1,
 	[BPF_ST | BPF_MEM | BPF_H] =	mem_st2,
 	[BPF_ST | BPF_MEM | BPF_W] =	mem_st4,
diff --git a/drivers/net/ethernet/netronome/nfp/bpf/main.h b/drivers/net/ethernet/netronome/nfp/bpf/main.h
index fac9c6f9e197..d0e17eebddd9 100644
--- a/drivers/net/ethernet/netronome/nfp/bpf/main.h
+++ b/drivers/net/ethernet/netronome/nfp/bpf/main.h
@@ -428,9 +428,9 @@ static inline bool is_mbpf_classic_store_pkt(const struct nfp_insn_meta *meta)
 	return is_mbpf_classic_store(meta) && meta->ptr.type == PTR_TO_PACKET;
 }
 
-static inline bool is_mbpf_xadd(const struct nfp_insn_meta *meta)
+static inline bool is_mbpf_atomic(const struct nfp_insn_meta *meta)
 {
-	return (meta->insn.code & ~BPF_SIZE_MASK) == (BPF_STX | BPF_XADD);
+	return (meta->insn.code & ~BPF_SIZE_MASK) == (BPF_STX | BPF_ATOMIC);
 }
 
 static inline bool is_mbpf_mul(const struct nfp_insn_meta *meta)
diff --git a/drivers/net/ethernet/netronome/nfp/bpf/verifier.c b/drivers/net/ethernet/netronome/nfp/bpf/verifier.c
index e92ee510fd52..9d235c0ce46a 100644
--- a/drivers/net/ethernet/netronome/nfp/bpf/verifier.c
+++ b/drivers/net/ethernet/netronome/nfp/bpf/verifier.c
@@ -479,7 +479,7 @@ nfp_bpf_check_ptr(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta,
 			pr_vlog(env, "map writes not supported\n");
 			return -EOPNOTSUPP;
 		}
-		if (is_mbpf_xadd(meta)) {
+		if (is_mbpf_atomic(meta)) {
 			err = nfp_bpf_map_mark_used(env, meta, reg,
 						    NFP_MAP_USE_ATOMIC_CNT);
 			if (err)
@@ -523,12 +523,17 @@ nfp_bpf_check_store(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta,
 }
 
 static int
-nfp_bpf_check_xadd(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta,
-		   struct bpf_verifier_env *env)
+nfp_bpf_check_atomic(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta,
+		     struct bpf_verifier_env *env)
 {
 	const struct bpf_reg_state *sreg = cur_regs(env) + meta->insn.src_reg;
 	const struct bpf_reg_state *dreg = cur_regs(env) + meta->insn.dst_reg;
 
+	if (meta->insn.imm != BPF_ADD) {
+		pr_vlog(env, "atomic op not implemented: %d\n", meta->insn.imm);
+		return -EOPNOTSUPP;
+	}
+
 	if (dreg->type != PTR_TO_MAP_VALUE) {
 		pr_vlog(env, "atomic add not to a map value pointer: %d\n",
 			dreg->type);
@@ -655,8 +660,8 @@ int nfp_verify_insn(struct bpf_verifier_env *env, int insn_idx,
 	if (is_mbpf_store(meta))
 		return nfp_bpf_check_store(nfp_prog, meta, env);
 
-	if (is_mbpf_xadd(meta))
-		return nfp_bpf_check_xadd(nfp_prog, meta, env);
+	if (is_mbpf_atomic(meta))
+		return nfp_bpf_check_atomic(nfp_prog, meta, env);
 
 	if (is_mbpf_alu(meta))
 		return nfp_bpf_check_alu(nfp_prog, meta, env);
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 1b62397bd124..ce19988fb312 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -261,13 +261,15 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
 
 /* Atomic memory add, *(uint *)(dst_reg + off16) += src_reg */
 
-#define BPF_STX_XADD(SIZE, DST, SRC, OFF)			\
+#define BPF_ATOMIC_ADD(SIZE, DST, SRC, OFF)			\
 	((struct bpf_insn) {					\
-		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_XADD,	\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
 		.dst_reg = DST,					\
 		.src_reg = SRC,					\
 		.off   = OFF,					\
-		.imm   = 0 })
+		.imm   = BPF_ADD })
+#define BPF_STX_XADD BPF_ATOMIC_ADD /* alias */
+
 
 /* Memory store, *(uint *) (dst_reg + off16) = imm32 */
 
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c3458ec1f30a..d0adc48db43c 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -19,7 +19,8 @@
 
 /* ld/ldx fields */
 #define BPF_DW		0x18	/* double word (64-bit) */
-#define BPF_XADD	0xc0	/* exclusive add */
+#define BPF_ATOMIC	0xc0	/* atomic memory ops - op type in immediate */
+#define BPF_XADD	0xc0	/* exclusive add - legacy name */
 
 /* alu/jmp fields */
 #define BPF_MOV		0xb0	/* mov reg to reg */
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index ff55cbcfbab4..1fbb13d30bbc 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1317,8 +1317,8 @@ EXPORT_SYMBOL_GPL(__bpf_call_base);
 	INSN_3(STX, MEM,  H),			\
 	INSN_3(STX, MEM,  W),			\
 	INSN_3(STX, MEM,  DW),			\
-	INSN_3(STX, XADD, W),			\
-	INSN_3(STX, XADD, DW),			\
+	INSN_3(STX, ATOMIC, W),			\
+	INSN_3(STX, ATOMIC, DW),		\
 	/*   Immediate based. */		\
 	INSN_3(ST, MEM, B),			\
 	INSN_3(ST, MEM, H),			\
@@ -1626,13 +1626,25 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
 	LDX_PROBE(DW, 8)
 #undef LDX_PROBE
 
-	STX_XADD_W: /* lock xadd *(u32 *)(dst_reg + off16) += src_reg */
-		atomic_add((u32) SRC, (atomic_t *)(unsigned long)
-			   (DST + insn->off));
+	STX_ATOMIC_W:
+		switch (IMM) {
+		case BPF_ADD:
+			/* lock xadd *(u32 *)(dst_reg + off16) += src_reg */
+			atomic_add((u32) SRC, (atomic_t *)(unsigned long)
+				   (DST + insn->off));
+		default:
+			goto default_label;
+		}
 		CONT;
-	STX_XADD_DW: /* lock xadd *(u64 *)(dst_reg + off16) += src_reg */
-		atomic64_add((u64) SRC, (atomic64_t *)(unsigned long)
-			     (DST + insn->off));
+	STX_ATOMIC_DW:
+		switch (IMM) {
+		case BPF_ADD:
+			/* lock xadd *(u64 *)(dst_reg + off16) += src_reg */
+			atomic64_add((u64) SRC, (atomic64_t *)(unsigned long)
+				     (DST + insn->off));
+		default:
+			goto default_label;
+		}
 		CONT;
 
 	default_label:
@@ -1642,7 +1654,8 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
 		 *
 		 * Note, verifier whitelists all opcodes in bpf_opcode_in_insntable().
 		 */
-		pr_warn("BPF interpreter: unknown opcode %02x\n", insn->code);
+		pr_warn("BPF interpreter: unknown opcode %02x (imm: 0x%x)\n",
+			insn->code, insn->imm);
 		BUG_ON(1);
 		return 0;
 }
diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c
index b44d8c447afd..37c8d6e9b4cc 100644
--- a/kernel/bpf/disasm.c
+++ b/kernel/bpf/disasm.c
@@ -153,14 +153,16 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs,
 				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
 				insn->dst_reg,
 				insn->off, insn->src_reg);
-		else if (BPF_MODE(insn->code) == BPF_XADD)
+		else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
+			 insn->imm == BPF_ADD) {
 			verbose(cbs->private_data, "(%02x) lock *(%s *)(r%d %+d) += r%d\n",
 				insn->code,
 				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
 				insn->dst_reg, insn->off,
 				insn->src_reg);
-		else
+		} else {
 			verbose(cbs->private_data, "BUG_%02x\n", insn->code);
+		}
 	} else if (class == BPF_ST) {
 		if (BPF_MODE(insn->code) != BPF_MEM) {
 			verbose(cbs->private_data, "BUG_st_%02x\n", insn->code);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e333ce43f281..1947da617b03 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3598,13 +3598,17 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 	return err;
 }
 
-static int check_xadd(struct bpf_verifier_env *env, int insn_idx, struct bpf_insn *insn)
+static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_insn *insn)
 {
 	int err;
 
-	if ((BPF_SIZE(insn->code) != BPF_W && BPF_SIZE(insn->code) != BPF_DW) ||
-	    insn->imm != 0) {
-		verbose(env, "BPF_XADD uses reserved fields\n");
+	if (insn->imm != BPF_ADD) {
+		verbose(env, "BPF_ATOMIC uses invalid atomic opcode %02x\n", insn->imm);
+		return -EINVAL;
+	}
+
+	if (BPF_SIZE(insn->code) != BPF_W && BPF_SIZE(insn->code) != BPF_DW) {
+		verbose(env, "invalid atomic operand size\n");
 		return -EINVAL;
 	}
 
@@ -3627,19 +3631,19 @@ static int check_xadd(struct bpf_verifier_env *env, int insn_idx, struct bpf_ins
 	    is_pkt_reg(env, insn->dst_reg) ||
 	    is_flow_key_reg(env, insn->dst_reg) ||
 	    is_sk_reg(env, insn->dst_reg)) {
-		verbose(env, "BPF_XADD stores into R%d %s is not allowed\n",
+		verbose(env, "atomic stores into R%d %s is not allowed\n",
 			insn->dst_reg,
 			reg_type_str[reg_state(env, insn->dst_reg)->type]);
 		return -EACCES;
 	}
 
-	/* check whether atomic_add can read the memory */
+	/* check whether we can read the memory */
 	err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
 			       BPF_SIZE(insn->code), BPF_READ, -1, true);
 	if (err)
 		return err;
 
-	/* check whether atomic_add can write into the same memory */
+	/* check whether we can write into the same memory */
 	return check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
 				BPF_SIZE(insn->code), BPF_WRITE, -1, true);
 }
@@ -9497,8 +9501,8 @@ static int do_check(struct bpf_verifier_env *env)
 		} else if (class == BPF_STX) {
 			enum bpf_reg_type *prev_dst_type, dst_reg_type;
 
-			if (BPF_MODE(insn->code) == BPF_XADD) {
-				err = check_xadd(env, env->insn_idx, insn);
+			if (BPF_MODE(insn->code) == BPF_ATOMIC) {
+				err = check_atomic(env, env->insn_idx, insn);
 				if (err)
 					return err;
 				env->insn_idx++;
@@ -9908,7 +9912,7 @@ static int resolve_pseudo_ldimm64(struct bpf_verifier_env *env)
 
 		if (BPF_CLASS(insn->code) == BPF_STX &&
 		    ((BPF_MODE(insn->code) != BPF_MEM &&
-		      BPF_MODE(insn->code) != BPF_XADD) || insn->imm != 0)) {
+		      BPF_MODE(insn->code) != BPF_ATOMIC) || insn->imm != 0)) {
 			verbose(env, "BPF_STX uses reserved fields\n");
 			return -EINVAL;
 		}
diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index ca7d635bccd9..fbb13ef9207c 100644
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -4295,7 +4295,7 @@ static struct bpf_test tests[] = {
 		{ { 0, 0xffffffff } },
 		.stack_depth = 40,
 	},
-	/* BPF_STX | BPF_XADD | BPF_W/DW */
+	/* BPF_STX | BPF_ATOMIC | BPF_W/DW */
 	{
 		"STX_XADD_W: Test: 0x12 + 0x10 = 0x22",
 		.u.insns_int = {
diff --git a/samples/bpf/bpf_insn.h b/samples/bpf/bpf_insn.h
index 544237980582..db67a2847395 100644
--- a/samples/bpf/bpf_insn.h
+++ b/samples/bpf/bpf_insn.h
@@ -138,11 +138,11 @@ struct bpf_insn;
 
 #define BPF_STX_XADD(SIZE, DST, SRC, OFF)			\
 	((struct bpf_insn) {					\
-		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_XADD,	\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
 		.dst_reg = DST,					\
 		.src_reg = SRC,					\
 		.off   = OFF,					\
-		.imm   = 0 })
+		.imm   = BPF_ADD })
 
 /* Memory store, *(uint *) (dst_reg + off16) = imm32 */
 
diff --git a/samples/bpf/sock_example.c b/samples/bpf/sock_example.c
index 00aae1d33fca..b18fa8083137 100644
--- a/samples/bpf/sock_example.c
+++ b/samples/bpf/sock_example.c
@@ -54,7 +54,7 @@ static int test_sock(void)
 		BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
 		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
 		BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */
-		BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */
+		BPF_ATOMIC_ADD(BPF_DW, BPF_REG_0, BPF_REG_1, 0),
 		BPF_MOV64_IMM(BPF_REG_0, 0), /* r0 = 0 */
 		BPF_EXIT_INSN(),
 	};
diff --git a/samples/bpf/test_cgrp2_attach.c b/samples/bpf/test_cgrp2_attach.c
index 20fbd1241db3..61896c4f9322 100644
--- a/samples/bpf/test_cgrp2_attach.c
+++ b/samples/bpf/test_cgrp2_attach.c
@@ -53,7 +53,7 @@ static int prog_load(int map_fd, int verdict)
 		BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
 		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
 		BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */
-		BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */
+		BPF_ATOMIC_ADD(BPF_DW, BPF_REG_0, BPF_REG_1, 0),
 
 		/* Count bytes */
 		BPF_MOV64_IMM(BPF_REG_0, MAP_KEY_BYTES), /* r0 = 1 */
@@ -64,7 +64,7 @@ static int prog_load(int map_fd, int verdict)
 		BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
 		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
 		BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_6, offsetof(struct __sk_buff, len)), /* r1 = skb->len */
-		BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */
+		BPF_ATOMIC_ADD(BPF_DW, BPF_REG_0, BPF_REG_1, 0),
 
 		BPF_MOV64_IMM(BPF_REG_0, verdict), /* r0 = verdict */
 		BPF_EXIT_INSN(),
diff --git a/tools/include/linux/filter.h b/tools/include/linux/filter.h
index ca28b6ab8db7..95ff51d97f25 100644
--- a/tools/include/linux/filter.h
+++ b/tools/include/linux/filter.h
@@ -171,13 +171,14 @@
 
 /* Atomic memory add, *(uint *)(dst_reg + off16) += src_reg */
 
-#define BPF_STX_XADD(SIZE, DST, SRC, OFF)			\
+#define BPF_ATOMIC_ADD(SIZE, DST, SRC, OFF)			\
 	((struct bpf_insn) {					\
-		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_XADD,	\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
 		.dst_reg = DST,					\
 		.src_reg = SRC,					\
 		.off   = OFF,					\
-		.imm   = 0 })
+		.imm   = BPF_ADD })
+#define BPF_STX_XADD BPF_ATOMIC_ADD /* alias */
 
 /* Memory store, *(uint *) (dst_reg + off16) = imm32 */
 
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index c3458ec1f30a..d0adc48db43c 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -19,7 +19,8 @@
 
 /* ld/ldx fields */
 #define BPF_DW		0x18	/* double word (64-bit) */
-#define BPF_XADD	0xc0	/* exclusive add */
+#define BPF_ATOMIC	0xc0	/* atomic memory ops - op type in immediate */
+#define BPF_XADD	0xc0	/* exclusive add - legacy name */
 
 /* alu/jmp fields */
 #define BPF_MOV		0xb0	/* mov reg to reg */
diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_attach_multi.c b/tools/testing/selftests/bpf/prog_tests/cgroup_attach_multi.c
index b549fcfacc0b..882fce827c81 100644
--- a/tools/testing/selftests/bpf/prog_tests/cgroup_attach_multi.c
+++ b/tools/testing/selftests/bpf/prog_tests/cgroup_attach_multi.c
@@ -45,13 +45,13 @@ static int prog_load_cnt(int verdict, int val)
 		BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
 		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
 		BPF_MOV64_IMM(BPF_REG_1, val), /* r1 = 1 */
-		BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */
+		BPF_ATOMIC_ADD(BPF_DW, BPF_REG_0, BPF_REG_1, 0),
 
 		BPF_LD_MAP_FD(BPF_REG_1, cgroup_storage_fd),
 		BPF_MOV64_IMM(BPF_REG_2, 0),
 		BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_get_local_storage),
 		BPF_MOV64_IMM(BPF_REG_1, val),
-		BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_W, BPF_REG_0, BPF_REG_1, 0, 0),
+		BPF_ATOMIC_ADD(BPF_W, BPF_REG_0, BPF_REG_1, 0),
 
 		BPF_LD_MAP_FD(BPF_REG_1, percpu_cgroup_storage_fd),
 		BPF_MOV64_IMM(BPF_REG_2, 0),
diff --git a/tools/testing/selftests/bpf/verifier/ctx.c b/tools/testing/selftests/bpf/verifier/ctx.c
index 93d6b1641481..a6d2d82b3447 100644
--- a/tools/testing/selftests/bpf/verifier/ctx.c
+++ b/tools/testing/selftests/bpf/verifier/ctx.c
@@ -10,14 +10,13 @@
 	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
 },
 {
-	"context stores via XADD",
+	"context stores via BPF_ATOMIC",
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_0, 0),
-	BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_W, BPF_REG_1,
-		     BPF_REG_0, offsetof(struct __sk_buff, mark), 0),
+	BPF_ATOMIC_ADD(BPF_W, BPF_REG_1, BPF_REG_0, offsetof(struct __sk_buff)),
 	BPF_EXIT_INSN(),
 	},
-	.errstr = "BPF_XADD stores into R1 ctx is not allowed",
+	.errstr = "BPF_ATOMIC stores into R1 ctx is not allowed",
 	.result = REJECT,
 	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
 },
diff --git a/tools/testing/selftests/bpf/verifier/leak_ptr.c b/tools/testing/selftests/bpf/verifier/leak_ptr.c
index d6eec17f2cd2..f9a594b48fb3 100644
--- a/tools/testing/selftests/bpf/verifier/leak_ptr.c
+++ b/tools/testing/selftests/bpf/verifier/leak_ptr.c
@@ -13,7 +13,7 @@
 	.errstr_unpriv = "R2 leaks addr into mem",
 	.result_unpriv = REJECT,
 	.result = REJECT,
-	.errstr = "BPF_XADD stores into R1 ctx is not allowed",
+	.errstr = "BPF_ATOMIC stores into R1 ctx is not allowed",
 },
 {
 	"leak pointer into ctx 2",
@@ -28,7 +28,7 @@
 	.errstr_unpriv = "R10 leaks addr into mem",
 	.result_unpriv = REJECT,
 	.result = REJECT,
-	.errstr = "BPF_XADD stores into R1 ctx is not allowed",
+	.errstr = "BPF_ATOMIC stores into R1 ctx is not allowed",
 },
 {
 	"leak pointer into ctx 3",
diff --git a/tools/testing/selftests/bpf/verifier/unpriv.c b/tools/testing/selftests/bpf/verifier/unpriv.c
index 91bb77c24a2e..85b5e8b70e5d 100644
--- a/tools/testing/selftests/bpf/verifier/unpriv.c
+++ b/tools/testing/selftests/bpf/verifier/unpriv.c
@@ -206,7 +206,8 @@
 	BPF_ALU64_IMM(BPF_ADD, BPF_REG_6, -8),
 	BPF_STX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, 0),
 	BPF_MOV64_IMM(BPF_REG_0, 1),
-	BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_10, BPF_REG_0, -8, 0),
+	BPF_RAW_INSN(BPF_STX | BPF_ATOMIC | BPF_DW,
+		     BPF_REG_10, BPF_REG_0, -8, BPF_ADD),
 	BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_6, 0),
 	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_get_hash_recalc),
 	BPF_EXIT_INSN(),
diff --git a/tools/testing/selftests/bpf/verifier/xadd.c b/tools/testing/selftests/bpf/verifier/xadd.c
index c5de2e62cc8b..70a320505bf2 100644
--- a/tools/testing/selftests/bpf/verifier/xadd.c
+++ b/tools/testing/selftests/bpf/verifier/xadd.c
@@ -51,7 +51,7 @@
 	BPF_EXIT_INSN(),
 	},
 	.result = REJECT,
-	.errstr = "BPF_XADD stores into R2 pkt is not allowed",
+	.errstr = "BPF_ATOMIC stores into R2 pkt is not allowed",
 	.prog_type = BPF_PROG_TYPE_XDP,
 	.flags = F_NEEDS_EFFICIENT_UNALIGNED_ACCESS,
 },
-- 
2.29.2.454.gaff20da3a2-goog

Re: [PATCH v2 bpf-next 05/13] bpf: Rename BPF_XADD and prepare to encode other atomics in .imm

[Yonghong Song]

On 11/27/20 9:57 AM, Brendan Jackman wrote:
> A subsequent patch will add additional atomic operations. These new
> operations will use the same opcode field as the existing XADD, with
> the immediate discriminating different operations.
> 
> In preparation, rename the instruction mode BPF_ATOMIC and start
> calling the zero immediate BPF_ADD.
> 
> This is possible (doesn't break existing valid BPF progs) because the
> immediate field is currently reserved MBZ and BPF_ADD is zero.
> 
> All uses are removed from the tree but the BPF_XADD definition is
> kept around to avoid breaking builds for people including kernel
> headers.
> 
> Signed-off-by: Brendan Jackman <jackmanb@google.com>
> ---
>   Documentation/networking/filter.rst           | 30 +++++++-----
>   arch/arm/net/bpf_jit_32.c                     |  7 ++-
>   arch/arm64/net/bpf_jit_comp.c                 | 16 +++++--
>   arch/mips/net/ebpf_jit.c                      | 11 +++--
>   arch/powerpc/net/bpf_jit_comp64.c             | 25 ++++++++--
>   arch/riscv/net/bpf_jit_comp32.c               | 20 ++++++--
>   arch/riscv/net/bpf_jit_comp64.c               | 16 +++++--
>   arch/s390/net/bpf_jit_comp.c                  | 27 ++++++-----
>   arch/sparc/net/bpf_jit_comp_64.c              | 17 +++++--
>   arch/x86/net/bpf_jit_comp.c                   | 46 ++++++++++++++-----
>   arch/x86/net/bpf_jit_comp32.c                 |  6 +--
>   drivers/net/ethernet/netronome/nfp/bpf/jit.c  | 14 ++++--
>   drivers/net/ethernet/netronome/nfp/bpf/main.h |  4 +-
>   .../net/ethernet/netronome/nfp/bpf/verifier.c | 15 ++++--
>   include/linux/filter.h                        |  8 ++--
>   include/uapi/linux/bpf.h                      |  3 +-
>   kernel/bpf/core.c                             | 31 +++++++++----
>   kernel/bpf/disasm.c                           |  6 ++-
>   kernel/bpf/verifier.c                         | 24 ++++++----
>   lib/test_bpf.c                                |  2 +-
>   samples/bpf/bpf_insn.h                        |  4 +-
>   samples/bpf/sock_example.c                    |  2 +-
>   samples/bpf/test_cgrp2_attach.c               |  4 +-
>   tools/include/linux/filter.h                  |  7 +--
>   tools/include/uapi/linux/bpf.h                |  3 +-
>   .../bpf/prog_tests/cgroup_attach_multi.c      |  4 +-
>   tools/testing/selftests/bpf/verifier/ctx.c    |  7 ++-
>   .../testing/selftests/bpf/verifier/leak_ptr.c |  4 +-
>   tools/testing/selftests/bpf/verifier/unpriv.c |  3 +-
>   tools/testing/selftests/bpf/verifier/xadd.c   |  2 +-
>   30 files changed, 248 insertions(+), 120 deletions(-)
> 
> diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst
[...]
> diff --git a/drivers/net/ethernet/netronome/nfp/bpf/jit.c b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
> index 0a721f6e8676..1c9efc74edfc 100644
> --- a/drivers/net/ethernet/netronome/nfp/bpf/jit.c
> +++ b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
> @@ -3109,13 +3109,19 @@ mem_xadd(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta, bool is64)
>   	return 0;
>   }
>   
> -static int mem_xadd4(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
> +static int mem_atomic4(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
>   {
> +	if (meta->insn.off != BPF_ADD)
> +		return -EOPNOTSUPP;

You probably missed this change. it should be meta->insn.imm != BPF_ADD.

> +
>   	return mem_xadd(nfp_prog, meta, false);
>   }
>   
> -static int mem_xadd8(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
> +static int mem_atomic8(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
>   {
> +	if (meta->insn.off != BPF_ADD)

same as above.

> +		return -EOPNOTSUPP;
> +
>   	return mem_xadd(nfp_prog, meta, true);
>   }
>   
> @@ -3475,8 +3481,8 @@ static const instr_cb_t instr_cb[256] = {
>   	[BPF_STX | BPF_MEM | BPF_H] =	mem_stx2,
>   	[BPF_STX | BPF_MEM | BPF_W] =	mem_stx4,
>   	[BPF_STX | BPF_MEM | BPF_DW] =	mem_stx8,
> -	[BPF_STX | BPF_XADD | BPF_W] =	mem_xadd4,
> -	[BPF_STX | BPF_XADD | BPF_DW] =	mem_xadd8,
> +	[BPF_STX | BPF_ATOMIC | BPF_W] =	mem_atomic4,
> +	[BPF_STX | BPF_ATOMIC | BPF_DW] =	mem_atomic8,
>   	[BPF_ST | BPF_MEM | BPF_B] =	mem_st1,
>   	[BPF_ST | BPF_MEM | BPF_H] =	mem_st2,
>   	[BPF_ST | BPF_MEM | BPF_W] =	mem_st4,
[...]

Re: [PATCH v2 bpf-next 05/13] bpf: Rename BPF_XADD and prepare to encode other atomics in .imm

[Brendan Jackman]

On Fri, Nov 27, 2020 at 07:43:46PM -0800, Yonghong Song wrote:
> 
> 
> On 11/27/20 9:57 AM, Brendan Jackman wrote:
> > diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst
> [...]
> > diff --git a/drivers/net/ethernet/netronome/nfp/bpf/jit.c b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
> > index 0a721f6e8676..1c9efc74edfc 100644
> > --- a/drivers/net/ethernet/netronome/nfp/bpf/jit.c
> > +++ b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
> > @@ -3109,13 +3109,19 @@ mem_xadd(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta, bool is64)
> >   	return 0;
> >   }
> > -static int mem_xadd4(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
> > +static int mem_atomic4(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
> >   {
> > +	if (meta->insn.off != BPF_ADD)
> > +		return -EOPNOTSUPP;
> 
> You probably missed this change. it should be meta->insn.imm != BPF_ADD.
> 
> > +
> >   	return mem_xadd(nfp_prog, meta, false);
> >   }
> > -static int mem_xadd8(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
> > +static int mem_atomic8(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
> >   {
> > +	if (meta->insn.off != BPF_ADD)
> 
> same as above.

Dang. Many thanks for the careful review!

[PATCH v2 bpf-next 06/13] bpf: Move BPF_STX reserved field check into BPF_STX verifier code

[Brendan Jackman]

I can't find a reason why this code is in resolve_pseudo_ldimm64;
since I'll be modifying it in a subsequent commit, tidy it up.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 kernel/bpf/verifier.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1947da617b03..e8b41ccdfb90 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9501,6 +9501,12 @@ static int do_check(struct bpf_verifier_env *env)
 		} else if (class == BPF_STX) {
 			enum bpf_reg_type *prev_dst_type, dst_reg_type;
 
+			if (((BPF_MODE(insn->code) != BPF_MEM &&
+			      BPF_MODE(insn->code) != BPF_ATOMIC) || insn->imm != 0)) {
+				verbose(env, "BPF_STX uses reserved fields\n");
+				return -EINVAL;
+			}
+
 			if (BPF_MODE(insn->code) == BPF_ATOMIC) {
 				err = check_atomic(env, env->insn_idx, insn);
 				if (err)
@@ -9910,13 +9916,6 @@ static int resolve_pseudo_ldimm64(struct bpf_verifier_env *env)
 			return -EINVAL;
 		}
 
-		if (BPF_CLASS(insn->code) == BPF_STX &&
-		    ((BPF_MODE(insn->code) != BPF_MEM &&
-		      BPF_MODE(insn->code) != BPF_ATOMIC) || insn->imm != 0)) {
-			verbose(env, "BPF_STX uses reserved fields\n");
-			return -EINVAL;
-		}
-
 		if (insn[0].code == (BPF_LD | BPF_IMM | BPF_DW)) {
 			struct bpf_insn_aux_data *aux;
 			struct bpf_map *map;
-- 
2.29.2.454.gaff20da3a2-goog

[PATCH v2 bpf-next 07/13] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction

[Brendan Jackman]

This value can be set in bpf_insn.imm, for BPF_ATOMIC instructions,
in order to have the previous value of the atomically-modified memory
location loaded into the src register after an atomic op is carried
out.

Suggested-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 arch/x86/net/bpf_jit_comp.c    |  4 ++++
 include/linux/filter.h         |  9 +++++++++
 include/uapi/linux/bpf.h       |  3 +++
 kernel/bpf/core.c              | 13 +++++++++++++
 kernel/bpf/disasm.c            |  7 +++++++
 kernel/bpf/verifier.c          | 35 ++++++++++++++++++++++++----------
 tools/include/linux/filter.h   | 10 ++++++++++
 tools/include/uapi/linux/bpf.h |  3 +++
 8 files changed, 74 insertions(+), 10 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 7c47ad70ddb4..d3cd45bcd0c1 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -827,6 +827,10 @@ static int emit_atomic(u8 **pprog, u8 atomic_op,
 		/* lock *(u32/u64*)(dst_reg + off) <op>= src_reg */
 		EMIT1(simple_alu_opcodes[atomic_op]);
 		break;
+	case BPF_ADD | BPF_FETCH:
+		/* src_reg = atomic_fetch_add(*(dst_reg + off), src_reg); */
+		EMIT2(0x0F, 0xC1);
+		break;
 	default:
 		pr_err("bpf_jit: unknown atomic opcode %02x\n", atomic_op);
 		return -EFAULT;
diff --git a/include/linux/filter.h b/include/linux/filter.h
index ce19988fb312..4e04d0fc454f 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -270,6 +270,15 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
 		.imm   = BPF_ADD })
 #define BPF_STX_XADD BPF_ATOMIC_ADD /* alias */
 
+/* Atomic memory add with fetch, src_reg = atomic_fetch_add(*(dst_reg + off), src_reg); */
+
+#define BPF_ATOMIC_FETCH_ADD(SIZE, DST, SRC, OFF)		\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_ADD | BPF_FETCH })
 
 /* Memory store, *(uint *) (dst_reg + off16) = imm32 */
 
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index d0adc48db43c..025e377e7229 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -44,6 +44,9 @@
 #define BPF_CALL	0x80	/* function call */
 #define BPF_EXIT	0x90	/* function return */
 
+/* atomic op type fields (stored in immediate) */
+#define BPF_FETCH	0x01	/* fetch previous value into src reg */
+
 /* Register numbers */
 enum {
 	BPF_REG_0 = 0,
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 1fbb13d30bbc..49a2a533db60 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1632,16 +1632,29 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
 			/* lock xadd *(u32 *)(dst_reg + off16) += src_reg */
 			atomic_add((u32) SRC, (atomic_t *)(unsigned long)
 				   (DST + insn->off));
+			break;
+		case BPF_ADD | BPF_FETCH:
+			SRC = (u32) atomic_fetch_add(
+				(u32) SRC,
+				(atomic_t *)(unsigned long) (DST + insn->off));
+			break;
 		default:
 			goto default_label;
 		}
 		CONT;
+
 	STX_ATOMIC_DW:
 		switch (IMM) {
 		case BPF_ADD:
 			/* lock xadd *(u64 *)(dst_reg + off16) += src_reg */
 			atomic64_add((u64) SRC, (atomic64_t *)(unsigned long)
 				     (DST + insn->off));
+			break;
+		case BPF_ADD | BPF_FETCH:
+			SRC = (u64) atomic64_fetch_add(
+				(u64) SRC,
+				(atomic64_t *)(s64) (DST + insn->off));
+			break;
 		default:
 			goto default_label;
 		}
diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c
index 37c8d6e9b4cc..3ee2246a52ef 100644
--- a/kernel/bpf/disasm.c
+++ b/kernel/bpf/disasm.c
@@ -160,6 +160,13 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs,
 				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
 				insn->dst_reg, insn->off,
 				insn->src_reg);
+		} else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
+			   insn->imm == (BPF_ADD | BPF_FETCH)) {
+			verbose(cbs->private_data, "(%02x) r%d = atomic%s_fetch_add(*(%s *)(r%d %+d), r%d)\n",
+				insn->code, insn->src_reg,
+				BPF_SIZE(insn->code) == BPF_DW ? "64" : "",
+				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
+				insn->dst_reg, insn->off, insn->src_reg);
 		} else {
 			verbose(cbs->private_data, "BUG_%02x\n", insn->code);
 		}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e8b41ccdfb90..cd4c03b25573 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3602,7 +3602,11 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
 {
 	int err;
 
-	if (insn->imm != BPF_ADD) {
+	switch (insn->imm) {
+	case BPF_ADD:
+	case BPF_ADD | BPF_FETCH:
+		break;
+	default:
 		verbose(env, "BPF_ATOMIC uses invalid atomic opcode %02x\n", insn->imm);
 		return -EINVAL;
 	}
@@ -3631,7 +3635,7 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
 	    is_pkt_reg(env, insn->dst_reg) ||
 	    is_flow_key_reg(env, insn->dst_reg) ||
 	    is_sk_reg(env, insn->dst_reg)) {
-		verbose(env, "atomic stores into R%d %s is not allowed\n",
+		verbose(env, "BPF_ATOMIC stores into R%d %s is not allowed\n",
 			insn->dst_reg,
 			reg_type_str[reg_state(env, insn->dst_reg)->type]);
 		return -EACCES;
@@ -3644,8 +3648,20 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
 		return err;
 
 	/* check whether we can write into the same memory */
-	return check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
-				BPF_SIZE(insn->code), BPF_WRITE, -1, true);
+	err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
+			       BPF_SIZE(insn->code), BPF_WRITE, -1, true);
+	if (err)
+		return err;
+
+	if (!(insn->imm & BPF_FETCH))
+		return 0;
+
+	/* check and record load of old value into src reg  */
+	err = check_reg_arg(env, insn->src_reg, DST_OP);
+	if (err)
+		return err;
+
+	return 0;
 }
 
 static int __check_stack_boundary(struct bpf_verifier_env *env, u32 regno,
@@ -9501,12 +9517,6 @@ static int do_check(struct bpf_verifier_env *env)
 		} else if (class == BPF_STX) {
 			enum bpf_reg_type *prev_dst_type, dst_reg_type;
 
-			if (((BPF_MODE(insn->code) != BPF_MEM &&
-			      BPF_MODE(insn->code) != BPF_ATOMIC) || insn->imm != 0)) {
-				verbose(env, "BPF_STX uses reserved fields\n");
-				return -EINVAL;
-			}
-
 			if (BPF_MODE(insn->code) == BPF_ATOMIC) {
 				err = check_atomic(env, env->insn_idx, insn);
 				if (err)
@@ -9515,6 +9525,11 @@ static int do_check(struct bpf_verifier_env *env)
 				continue;
 			}
 
+			if (BPF_MODE(insn->code) != BPF_MEM && insn->imm != 0) {
+				verbose(env, "BPF_STX uses reserved fields\n");
+				return -EINVAL;
+			}
+
 			/* check src1 operand */
 			err = check_reg_arg(env, insn->src_reg, SRC_OP);
 			if (err)
diff --git a/tools/include/linux/filter.h b/tools/include/linux/filter.h
index 95ff51d97f25..ac7701678e1a 100644
--- a/tools/include/linux/filter.h
+++ b/tools/include/linux/filter.h
@@ -180,6 +180,16 @@
 		.imm   = BPF_ADD })
 #define BPF_STX_XADD BPF_ATOMIC_ADD /* alias */
 
+/* Atomic memory add with fetch, src_reg = atomic_fetch_add(*(dst_reg + off), src_reg); */
+
+#define BPF_ATOMIC_FETCH_ADD(SIZE, DST, SRC, OFF)		\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_ADD | BPF_FETCH })
+
 /* Memory store, *(uint *) (dst_reg + off16) = imm32 */
 
 #define BPF_ST_MEM(SIZE, DST, OFF, IMM)				\
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index d0adc48db43c..025e377e7229 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -44,6 +44,9 @@
 #define BPF_CALL	0x80	/* function call */
 #define BPF_EXIT	0x90	/* function return */
 
+/* atomic op type fields (stored in immediate) */
+#define BPF_FETCH	0x01	/* fetch previous value into src reg */
+
 /* Register numbers */
 enum {
 	BPF_REG_0 = 0,
-- 
2.29.2.454.gaff20da3a2-goog

Re: [PATCH v2 bpf-next 07/13] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction

[Yonghong Song]

On 11/27/20 9:57 AM, Brendan Jackman wrote:
> This value can be set in bpf_insn.imm, for BPF_ATOMIC instructions,
> in order to have the previous value of the atomically-modified memory
> location loaded into the src register after an atomic op is carried
> out.
> 
> Suggested-by: Yonghong Song <yhs@fb.com>
> Signed-off-by: Brendan Jackman <jackmanb@google.com>
> ---
>   arch/x86/net/bpf_jit_comp.c    |  4 ++++
>   include/linux/filter.h         |  9 +++++++++
>   include/uapi/linux/bpf.h       |  3 +++
>   kernel/bpf/core.c              | 13 +++++++++++++
>   kernel/bpf/disasm.c            |  7 +++++++
>   kernel/bpf/verifier.c          | 35 ++++++++++++++++++++++++----------
>   tools/include/linux/filter.h   | 10 ++++++++++
>   tools/include/uapi/linux/bpf.h |  3 +++
>   8 files changed, 74 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 7c47ad70ddb4..d3cd45bcd0c1 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -827,6 +827,10 @@ static int emit_atomic(u8 **pprog, u8 atomic_op,
>   		/* lock *(u32/u64*)(dst_reg + off) <op>= src_reg */
>   		EMIT1(simple_alu_opcodes[atomic_op]);
>   		break;
> +	case BPF_ADD | BPF_FETCH:
> +		/* src_reg = atomic_fetch_add(*(dst_reg + off), src_reg); */
> +		EMIT2(0x0F, 0xC1);
> +		break;
>   	default:
>   		pr_err("bpf_jit: unknown atomic opcode %02x\n", atomic_op);
>   		return -EFAULT;
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index ce19988fb312..4e04d0fc454f 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -270,6 +270,15 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
>   		.imm   = BPF_ADD })
>   #define BPF_STX_XADD BPF_ATOMIC_ADD /* alias */
>   
> +/* Atomic memory add with fetch, src_reg = atomic_fetch_add(*(dst_reg + off), src_reg); */
> +
> +#define BPF_ATOMIC_FETCH_ADD(SIZE, DST, SRC, OFF)		\
> +	((struct bpf_insn) {					\
> +		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
> +		.dst_reg = DST,					\
> +		.src_reg = SRC,					\
> +		.off   = OFF,					\
> +		.imm   = BPF_ADD | BPF_FETCH })
>   
>   /* Memory store, *(uint *) (dst_reg + off16) = imm32 */
>   
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index d0adc48db43c..025e377e7229 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -44,6 +44,9 @@
>   #define BPF_CALL	0x80	/* function call */
>   #define BPF_EXIT	0x90	/* function return */
>   
> +/* atomic op type fields (stored in immediate) */
> +#define BPF_FETCH	0x01	/* fetch previous value into src reg */
> +
>   /* Register numbers */
>   enum {
>   	BPF_REG_0 = 0,
[...]
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index e8b41ccdfb90..cd4c03b25573 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -3602,7 +3602,11 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
>   {
>   	int err;
>   
> -	if (insn->imm != BPF_ADD) {
> +	switch (insn->imm) {
> +	case BPF_ADD:
> +	case BPF_ADD | BPF_FETCH:
> +		break;
> +	default:
>   		verbose(env, "BPF_ATOMIC uses invalid atomic opcode %02x\n", insn->imm);
>   		return -EINVAL;
>   	}
> @@ -3631,7 +3635,7 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
>   	    is_pkt_reg(env, insn->dst_reg) ||
>   	    is_flow_key_reg(env, insn->dst_reg) ||
>   	    is_sk_reg(env, insn->dst_reg)) {
> -		verbose(env, "atomic stores into R%d %s is not allowed\n",
> +		verbose(env, "BPF_ATOMIC stores into R%d %s is not allowed\n",
>   			insn->dst_reg,
>   			reg_type_str[reg_state(env, insn->dst_reg)->type]);
>   		return -EACCES;
> @@ -3644,8 +3648,20 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
>   		return err;
>   
>   	/* check whether we can write into the same memory */
> -	return check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
> -				BPF_SIZE(insn->code), BPF_WRITE, -1, true);
> +	err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
> +			       BPF_SIZE(insn->code), BPF_WRITE, -1, true);
> +	if (err)
> +		return err;
> +
> +	if (!(insn->imm & BPF_FETCH))
> +		return 0;
> +
> +	/* check and record load of old value into src reg  */
> +	err = check_reg_arg(env, insn->src_reg, DST_OP);
> +	if (err)
> +		return err;
> +
> +	return 0;
>   }
>   
>   static int __check_stack_boundary(struct bpf_verifier_env *env, u32 regno,
> @@ -9501,12 +9517,6 @@ static int do_check(struct bpf_verifier_env *env)
>   		} else if (class == BPF_STX) {
>   			enum bpf_reg_type *prev_dst_type, dst_reg_type;
>   
> -			if (((BPF_MODE(insn->code) != BPF_MEM &&
> -			      BPF_MODE(insn->code) != BPF_ATOMIC) || insn->imm != 0)) {
> -				verbose(env, "BPF_STX uses reserved fields\n");
> -				return -EINVAL;
> -			}
> -
>   			if (BPF_MODE(insn->code) == BPF_ATOMIC) {
>   				err = check_atomic(env, env->insn_idx, insn);
>   				if (err)
> @@ -9515,6 +9525,11 @@ static int do_check(struct bpf_verifier_env *env)
>   				continue;
>   			}
>   
> +			if (BPF_MODE(insn->code) != BPF_MEM && insn->imm != 0) {

"||" here instead of "&&"?

> +				verbose(env, "BPF_STX uses reserved fields\n");
> +				return -EINVAL;
> +			}
> +
>   			/* check src1 operand */
>   			err = check_reg_arg(env, insn->src_reg, SRC_OP);
>   			if (err)
> diff --git a/tools/include/linux/filter.h b/tools/include/linux/filter.h
[...]

Re: [PATCH v2 bpf-next 07/13] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction

[Brendan Jackman]

On Fri, Nov 27, 2020 at 08:15:49PM -0800, Yonghong Song wrote:
> 
> 
> On 11/27/20 9:57 AM, Brendan Jackman wrote:
[...]
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index e8b41ccdfb90..cd4c03b25573 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -3602,7 +3602,11 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
> >   {
> >   	int err;
> > -	if (insn->imm != BPF_ADD) {
> > +	switch (insn->imm) {
> > +	case BPF_ADD:
> > +	case BPF_ADD | BPF_FETCH:
> > +		break;
> > +	default:
> >   		verbose(env, "BPF_ATOMIC uses invalid atomic opcode %02x\n", insn->imm);
> >   		return -EINVAL;
> >   	}
> > @@ -3631,7 +3635,7 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
> >   	    is_pkt_reg(env, insn->dst_reg) ||
> >   	    is_flow_key_reg(env, insn->dst_reg) ||
> >   	    is_sk_reg(env, insn->dst_reg)) {
> > -		verbose(env, "atomic stores into R%d %s is not allowed\n",
> > +		verbose(env, "BPF_ATOMIC stores into R%d %s is not allowed\n",
> >   			insn->dst_reg,
> >   			reg_type_str[reg_state(env, insn->dst_reg)->type]);
> >   		return -EACCES;
> > @@ -3644,8 +3648,20 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
> >   		return err;
> >   	/* check whether we can write into the same memory */
> > -	return check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
> > -				BPF_SIZE(insn->code), BPF_WRITE, -1, true);
> > +	err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
> > +			       BPF_SIZE(insn->code), BPF_WRITE, -1, true);
> > +	if (err)
> > +		return err;
> > +
> > +	if (!(insn->imm & BPF_FETCH))
> > +		return 0;
> > +
> > +	/* check and record load of old value into src reg  */
> > +	err = check_reg_arg(env, insn->src_reg, DST_OP);
> > +	if (err)
> > +		return err;
> > +
> > +	return 0;
> >   }
> >   static int __check_stack_boundary(struct bpf_verifier_env *env, u32 regno,
> > @@ -9501,12 +9517,6 @@ static int do_check(struct bpf_verifier_env *env)
> >   		} else if (class == BPF_STX) {
> >   			enum bpf_reg_type *prev_dst_type, dst_reg_type;
> > -			if (((BPF_MODE(insn->code) != BPF_MEM &&
> > -			      BPF_MODE(insn->code) != BPF_ATOMIC) || insn->imm != 0)) {
> > -				verbose(env, "BPF_STX uses reserved fields\n");
> > -				return -EINVAL;
> > -			}
> > -
> >   			if (BPF_MODE(insn->code) == BPF_ATOMIC) {
> >   				err = check_atomic(env, env->insn_idx, insn);
> >   				if (err)
> > @@ -9515,6 +9525,11 @@ static int do_check(struct bpf_verifier_env *env)
> >   				continue;
> >   			}
> > +			if (BPF_MODE(insn->code) != BPF_MEM && insn->imm != 0) {
> 
> "||" here instead of "&&"?

Right - thanks again!

[PATCH v2 bpf-next 08/13] bpf: Add instructions for atomic_[cmp]xchg

[Brendan Jackman]

This adds two atomic opcodes, both of which include the BPF_FETCH
flag. XCHG without the BPF_FETCh flag would naturally encode
atomic_set. This is not supported because it would be of limited
value to userspace (it doesn't imply any barriers). CMPXCHG without
BPF_FETCH woulud be an atomic compare-and-write. We don't have such
an operation in the kernel so it isn't provided to BPF either.

There are two significant design decisions made for the CMPXCHG
instruction:

 - To solve the issue that this operation fundamentally has 3
   operands, but we only have two register fields. Therefore the
   operand we compare against (the kernel's API calls it 'old') is
   hard-coded to be R0. x86 has similar design (and A64 doesn't
   have this problem).

   A potential alternative might be to encode the other operand's
   register number in the immediate field.

 - The kernel's atomic_cmpxchg returns the old value, while the C11
   userspace APIs return a boolean indicating the comparison
   result. Which should BPF do? A64 returns the old value. x86 returns
   the old value in the hard-coded register (and also sets a
   flag). That means return-old-value is easier to JIT.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 arch/x86/net/bpf_jit_comp.c    |  8 ++++++++
 include/linux/filter.h         | 20 ++++++++++++++++++++
 include/uapi/linux/bpf.h       |  4 +++-
 kernel/bpf/core.c              | 20 ++++++++++++++++++++
 kernel/bpf/disasm.c            | 15 +++++++++++++++
 kernel/bpf/verifier.c          | 19 +++++++++++++++++--
 tools/include/linux/filter.h   | 20 ++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  4 +++-
 8 files changed, 106 insertions(+), 4 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index d3cd45bcd0c1..7431b2937157 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -831,6 +831,14 @@ static int emit_atomic(u8 **pprog, u8 atomic_op,
 		/* src_reg = atomic_fetch_add(*(dst_reg + off), src_reg); */
 		EMIT2(0x0F, 0xC1);
 		break;
+	case BPF_XCHG:
+		/* src_reg = atomic_xchg(*(u32/u64*)(dst_reg + off), src_reg); */
+		EMIT1(0x87);
+		break;
+	case BPF_CMPXCHG:
+		/* r0 = atomic_cmpxchg(*(u32/u64*)(dst_reg + off), r0, src_reg); */
+		EMIT2(0x0F, 0xB1);
+		break;
 	default:
 		pr_err("bpf_jit: unknown atomic opcode %02x\n", atomic_op);
 		return -EFAULT;
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 4e04d0fc454f..6186280715ed 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -280,6 +280,26 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
 		.off   = OFF,					\
 		.imm   = BPF_ADD | BPF_FETCH })
 
+/* Atomic exchange, src_reg = atomic_xchg((dst_reg + off), src_reg) */
+
+#define BPF_ATOMIC_XCHG(SIZE, DST, SRC, OFF)			\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_XCHG  })
+
+/* Atomic compare-exchange, r0 = atomic_cmpxchg((dst_reg + off), r0, src_reg) */
+
+#define BPF_ATOMIC_CMPXCHG(SIZE, DST, SRC, OFF)			\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_CMPXCHG })
+
 /* Memory store, *(uint *) (dst_reg + off16) = imm32 */
 
 #define BPF_ST_MEM(SIZE, DST, OFF, IMM)				\
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 025e377e7229..82039a1176ac 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -45,7 +45,9 @@
 #define BPF_EXIT	0x90	/* function return */
 
 /* atomic op type fields (stored in immediate) */
-#define BPF_FETCH	0x01	/* fetch previous value into src reg */
+#define BPF_XCHG	(0xe0 | BPF_FETCH)	/* atomic exchange */
+#define BPF_CMPXCHG	(0xf0 | BPF_FETCH)	/* atomic compare-and-write */
+#define BPF_FETCH	0x01	/* fetch previous value into src reg or r0*/
 
 /* Register numbers */
 enum {
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 49a2a533db60..05350a8f87c0 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1638,6 +1638,16 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
 				(u32) SRC,
 				(atomic_t *)(unsigned long) (DST + insn->off));
 			break;
+		case BPF_XCHG:
+			SRC = (u32) atomic_xchg(
+				(atomic_t *)(unsigned long) (DST + insn->off),
+				(u32) SRC);
+			break;
+		case BPF_CMPXCHG:
+			BPF_R0 = (u32) atomic_cmpxchg(
+				(atomic_t *)(unsigned long) (DST + insn->off),
+				(u32) BPF_R0, (u32) SRC);
+			break;
 		default:
 			goto default_label;
 		}
@@ -1655,6 +1665,16 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
 				(u64) SRC,
 				(atomic64_t *)(s64) (DST + insn->off));
 			break;
+		case BPF_XCHG:
+			SRC = (u64) atomic64_xchg(
+				(atomic64_t *)(u64) (DST + insn->off),
+				(u64) SRC);
+			break;
+		case BPF_CMPXCHG:
+			BPF_R0 = (u64) atomic64_cmpxchg(
+				(atomic64_t *)(u64) (DST + insn->off),
+				(u64) BPF_R0, (u64) SRC);
+			break;
 		default:
 			goto default_label;
 		}
diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c
index 3ee2246a52ef..3441ac54ac65 100644
--- a/kernel/bpf/disasm.c
+++ b/kernel/bpf/disasm.c
@@ -167,6 +167,21 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs,
 				BPF_SIZE(insn->code) == BPF_DW ? "64" : "",
 				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
 				insn->dst_reg, insn->off, insn->src_reg);
+		} else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
+			   insn->imm == (BPF_CMPXCHG)) {
+			verbose(cbs->private_data, "(%02x) r0 = atomic%s_cmpxchg(*(%s *)(r%d %+d), r0, r%d)\n",
+				insn->code,
+				BPF_SIZE(insn->code) == BPF_DW ? "64" : "",
+				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
+				insn->dst_reg, insn->off,
+				insn->src_reg);
+		} else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
+			   insn->imm == (BPF_XCHG)) {
+			verbose(cbs->private_data, "(%02x) r%d = atomic%s_xchg(*(%s *)(r%d %+d), r%d)\n",
+				insn->code, insn->src_reg,
+				BPF_SIZE(insn->code) == BPF_DW ? "64" : "",
+				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
+				insn->dst_reg, insn->off, insn->src_reg);
 		} else {
 			verbose(cbs->private_data, "BUG_%02x\n", insn->code);
 		}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index cd4c03b25573..c8311cc114ec 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3601,10 +3601,13 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_insn *insn)
 {
 	int err;
+	int load_reg;
 
 	switch (insn->imm) {
 	case BPF_ADD:
 	case BPF_ADD | BPF_FETCH:
+	case BPF_XCHG:
+	case BPF_CMPXCHG:
 		break;
 	default:
 		verbose(env, "BPF_ATOMIC uses invalid atomic opcode %02x\n", insn->imm);
@@ -3626,6 +3629,13 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
 	if (err)
 		return err;
 
+	if (insn->imm == BPF_CMPXCHG) {
+		/* check src3 operand */
+		err = check_reg_arg(env, BPF_REG_0, SRC_OP);
+		if (err)
+			return err;
+	}
+
 	if (is_pointer_value(env, insn->src_reg)) {
 		verbose(env, "R%d leaks addr into mem\n", insn->src_reg);
 		return -EACCES;
@@ -3656,8 +3666,13 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
 	if (!(insn->imm & BPF_FETCH))
 		return 0;
 
-	/* check and record load of old value into src reg  */
-	err = check_reg_arg(env, insn->src_reg, DST_OP);
+	if (insn->imm == BPF_CMPXCHG)
+		load_reg = BPF_REG_0;
+	else
+		load_reg = insn->src_reg;
+
+	/* check and record load of old value */
+	err = check_reg_arg(env, load_reg, DST_OP);
 	if (err)
 		return err;
 
diff --git a/tools/include/linux/filter.h b/tools/include/linux/filter.h
index ac7701678e1a..ea99bd17d003 100644
--- a/tools/include/linux/filter.h
+++ b/tools/include/linux/filter.h
@@ -190,6 +190,26 @@
 		.off   = OFF,					\
 		.imm   = BPF_ADD | BPF_FETCH })
 
+/* Atomic exchange, src_reg = atomic_xchg((dst_reg + off), src_reg) */
+
+#define BPF_ATOMIC_XCHG(SIZE, DST, SRC, OFF)			\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_XCHG })
+
+/* Atomic compare-exchange, r0 = atomic_cmpxchg((dst_reg + off), r0, src_reg) */
+
+#define BPF_ATOMIC_CMPXCHG(SIZE, DST, SRC, OFF)			\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_CMPXCHG })
+
 /* Memory store, *(uint *) (dst_reg + off16) = imm32 */
 
 #define BPF_ST_MEM(SIZE, DST, OFF, IMM)				\
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 025e377e7229..82039a1176ac 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -45,7 +45,9 @@
 #define BPF_EXIT	0x90	/* function return */
 
 /* atomic op type fields (stored in immediate) */
-#define BPF_FETCH	0x01	/* fetch previous value into src reg */
+#define BPF_XCHG	(0xe0 | BPF_FETCH)	/* atomic exchange */
+#define BPF_CMPXCHG	(0xf0 | BPF_FETCH)	/* atomic compare-and-write */
+#define BPF_FETCH	0x01	/* fetch previous value into src reg or r0*/
 
 /* Register numbers */
 enum {
-- 
2.29.2.454.gaff20da3a2-goog

Re: [PATCH v2 bpf-next 08/13] bpf: Add instructions for atomic_[cmp]xchg

[Yonghong Song]

On 11/27/20 9:57 AM, Brendan Jackman wrote:
> This adds two atomic opcodes, both of which include the BPF_FETCH
> flag. XCHG without the BPF_FETCh flag would naturally encode

BPF_FETCH

> atomic_set. This is not supported because it would be of limited
> value to userspace (it doesn't imply any barriers). CMPXCHG without
> BPF_FETCH woulud be an atomic compare-and-write. We don't have such
> an operation in the kernel so it isn't provided to BPF either.
> 
> There are two significant design decisions made for the CMPXCHG
> instruction:
> 
>   - To solve the issue that this operation fundamentally has 3
>     operands, but we only have two register fields. Therefore the
>     operand we compare against (the kernel's API calls it 'old') is
>     hard-coded to be R0. x86 has similar design (and A64 doesn't
>     have this problem).
> 
>     A potential alternative might be to encode the other operand's
>     register number in the immediate field.
> 
>   - The kernel's atomic_cmpxchg returns the old value, while the C11
>     userspace APIs return a boolean indicating the comparison
>     result. Which should BPF do? A64 returns the old value. x86 returns
>     the old value in the hard-coded register (and also sets a
>     flag). That means return-old-value is easier to JIT.
> 
> Signed-off-by: Brendan Jackman <jackmanb@google.com>
> ---
>   arch/x86/net/bpf_jit_comp.c    |  8 ++++++++
>   include/linux/filter.h         | 20 ++++++++++++++++++++
>   include/uapi/linux/bpf.h       |  4 +++-
>   kernel/bpf/core.c              | 20 ++++++++++++++++++++
>   kernel/bpf/disasm.c            | 15 +++++++++++++++
>   kernel/bpf/verifier.c          | 19 +++++++++++++++++--
>   tools/include/linux/filter.h   | 20 ++++++++++++++++++++
>   tools/include/uapi/linux/bpf.h |  4 +++-
>   8 files changed, 106 insertions(+), 4 deletions(-)
> 
[...]
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index cd4c03b25573..c8311cc114ec 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -3601,10 +3601,13 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
>   static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_insn *insn)
>   {
>   	int err;
> +	int load_reg;
>   
>   	switch (insn->imm) {
>   	case BPF_ADD:
>   	case BPF_ADD | BPF_FETCH:
> +	case BPF_XCHG:
> +	case BPF_CMPXCHG:
>   		break;
>   	default:
>   		verbose(env, "BPF_ATOMIC uses invalid atomic opcode %02x\n", insn->imm);
> @@ -3626,6 +3629,13 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
>   	if (err)
>   		return err;
>   
> +	if (insn->imm == BPF_CMPXCHG) {
> +		/* check src3 operand */

better comment about what src3 means here?

> +		err = check_reg_arg(env, BPF_REG_0, SRC_OP);
> +		if (err)
> +			return err;
> +	}
> +
>   	if (is_pointer_value(env, insn->src_reg)) {
>   		verbose(env, "R%d leaks addr into mem\n", insn->src_reg);
>   		return -EACCES;
> @@ -3656,8 +3666,13 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
>   	if (!(insn->imm & BPF_FETCH))
>   		return 0;
>   
> -	/* check and record load of old value into src reg  */
> -	err = check_reg_arg(env, insn->src_reg, DST_OP);
> +	if (insn->imm == BPF_CMPXCHG)
> +		load_reg = BPF_REG_0;
> +	else
> +		load_reg = insn->src_reg;
> +
> +	/* check and record load of old value */
> +	err = check_reg_arg(env, load_reg, DST_OP);
>   	if (err)
>   		return err;
>   
[...]

Re: [PATCH v2 bpf-next 08/13] bpf: Add instructions for atomic_[cmp]xchg

[Brendan Jackman]

On Fri, Nov 27, 2020 at 09:25:53PM -0800, Yonghong Song wrote:
> 
> 
> On 11/27/20 9:57 AM, Brendan Jackman wrote:
> > This adds two atomic opcodes, both of which include the BPF_FETCH
> > flag. XCHG without the BPF_FETCh flag would naturally encode
> 
> BPF_FETCH

Ack, thanks

> > atomic_set. This is not supported because it would be of limited
> > value to userspace (it doesn't imply any barriers). CMPXCHG without
> > BPF_FETCH woulud be an atomic compare-and-write. We don't have such
> > an operation in the kernel so it isn't provided to BPF either.
> > 
> > There are two significant design decisions made for the CMPXCHG
> > instruction:
> > 
> >   - To solve the issue that this operation fundamentally has 3
> >     operands, but we only have two register fields. Therefore the
> >     operand we compare against (the kernel's API calls it 'old') is
> >     hard-coded to be R0. x86 has similar design (and A64 doesn't
> >     have this problem).
> > 
> >     A potential alternative might be to encode the other operand's
> >     register number in the immediate field.
> > 
> >   - The kernel's atomic_cmpxchg returns the old value, while the C11
> >     userspace APIs return a boolean indicating the comparison
> >     result. Which should BPF do? A64 returns the old value. x86 returns
> >     the old value in the hard-coded register (and also sets a
> >     flag). That means return-old-value is easier to JIT.
> > 
> > Signed-off-by: Brendan Jackman <jackmanb@google.com>
> > ---
> >   arch/x86/net/bpf_jit_comp.c    |  8 ++++++++
> >   include/linux/filter.h         | 20 ++++++++++++++++++++
> >   include/uapi/linux/bpf.h       |  4 +++-
> >   kernel/bpf/core.c              | 20 ++++++++++++++++++++
> >   kernel/bpf/disasm.c            | 15 +++++++++++++++
> >   kernel/bpf/verifier.c          | 19 +++++++++++++++++--
> >   tools/include/linux/filter.h   | 20 ++++++++++++++++++++
> >   tools/include/uapi/linux/bpf.h |  4 +++-
> >   8 files changed, 106 insertions(+), 4 deletions(-)
> > 
> [...]
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index cd4c03b25573..c8311cc114ec 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -3601,10 +3601,13 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
> >   static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_insn *insn)
> >   {
> >   	int err;
> > +	int load_reg;
> >   	switch (insn->imm) {
> >   	case BPF_ADD:
> >   	case BPF_ADD | BPF_FETCH:
> > +	case BPF_XCHG:
> > +	case BPF_CMPXCHG:
> >   		break;
> >   	default:
> >   		verbose(env, "BPF_ATOMIC uses invalid atomic opcode %02x\n", insn->imm);
> > @@ -3626,6 +3629,13 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
> >   	if (err)
> >   		return err;
> > +	if (insn->imm == BPF_CMPXCHG) {
> > +		/* check src3 operand */
> 
> better comment about what src3 means here?

Ack,  adding "Check comparison of R0 with memory location"

Re: [PATCH v2 bpf-next 08/13] bpf: Add instructions for atomic_[cmp]xchg

[Alexei Starovoitov]

On Fri, Nov 27, 2020 at 05:57:33PM +0000, Brendan Jackman wrote:
>  
>  /* atomic op type fields (stored in immediate) */
> -#define BPF_FETCH	0x01	/* fetch previous value into src reg */
> +#define BPF_XCHG	(0xe0 | BPF_FETCH)	/* atomic exchange */
> +#define BPF_CMPXCHG	(0xf0 | BPF_FETCH)	/* atomic compare-and-write */
> +#define BPF_FETCH	0x01	/* fetch previous value into src reg or r0*/

I think such comment is more confusing than helpful.
I'd just say that the fetch bit is not valid on its own.
It's used to build other instructions like cmpxchg and atomic_fetch_add.

> +		} else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
> +			   insn->imm == (BPF_CMPXCHG)) {

redundant ().

> +			verbose(cbs->private_data, "(%02x) r0 = atomic%s_cmpxchg(*(%s *)(r%d %+d), r0, r%d)\n",
> +				insn->code,
> +				BPF_SIZE(insn->code) == BPF_DW ? "64" : "",
> +				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
> +				insn->dst_reg, insn->off,
> +				insn->src_reg);
> +		} else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
> +			   insn->imm == (BPF_XCHG)) {

redundant ().

Re: [PATCH v2 bpf-next 08/13] bpf: Add instructions for atomic_[cmp]xchg

[Brendan Jackman]

On Sat, Nov 28, 2020 at 05:27:48PM -0800, Alexei Starovoitov wrote:
> On Fri, Nov 27, 2020 at 05:57:33PM +0000, Brendan Jackman wrote:
> >  
> >  /* atomic op type fields (stored in immediate) */
> > -#define BPF_FETCH	0x01	/* fetch previous value into src reg */
> > +#define BPF_XCHG	(0xe0 | BPF_FETCH)	/* atomic exchange */
> > +#define BPF_CMPXCHG	(0xf0 | BPF_FETCH)	/* atomic compare-and-write */
> > +#define BPF_FETCH	0x01	/* fetch previous value into src reg or r0*/
> 
> I think such comment is more confusing than helpful.
> I'd just say that the fetch bit is not valid on its own.
> It's used to build other instructions like cmpxchg and atomic_fetch_add.

OK sounds good.

> > +		} else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
> > +			   insn->imm == (BPF_CMPXCHG)) {
> 
> redundant ().

Ack, thanks

> > +			verbose(cbs->private_data, "(%02x) r0 = atomic%s_cmpxchg(*(%s *)(r%d %+d), r0, r%d)\n",
> > +				insn->code,
> > +				BPF_SIZE(insn->code) == BPF_DW ? "64" : "",
> > +				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
> > +				insn->dst_reg, insn->off,
> > +				insn->src_reg);
> > +		} else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
> > +			   insn->imm == (BPF_XCHG)) {
> 
> redundant ().

Ack, thanks

[PATCH v2 bpf-next 09/13] bpf: Pull out a macro for interpreting atomic ALU operations

[Brendan Jackman]

Since the atomic operations that are added in subsequent commits are
all isomorphic with BPF_ADD, pull out a macro to avoid the
interpreter becoming dominated by lines of atomic-related code.

Note that this sacrificies interpreter performance (combining
STX_ATOMIC_W and STX_ATOMIC_DW into single switch case means that we
need an extra conditional branch to differentiate them) in favour of
compact and (relatively!) simple C code.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 kernel/bpf/core.c | 79 +++++++++++++++++++++++------------------------
 1 file changed, 38 insertions(+), 41 deletions(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 05350a8f87c0..20a5351d1dc2 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1626,55 +1626,52 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
 	LDX_PROBE(DW, 8)
 #undef LDX_PROBE
 
-	STX_ATOMIC_W:
-		switch (IMM) {
-		case BPF_ADD:
-			/* lock xadd *(u32 *)(dst_reg + off16) += src_reg */
-			atomic_add((u32) SRC, (atomic_t *)(unsigned long)
-				   (DST + insn->off));
-			break;
-		case BPF_ADD | BPF_FETCH:
-			SRC = (u32) atomic_fetch_add(
-				(u32) SRC,
-				(atomic_t *)(unsigned long) (DST + insn->off));
-			break;
-		case BPF_XCHG:
-			SRC = (u32) atomic_xchg(
-				(atomic_t *)(unsigned long) (DST + insn->off),
-				(u32) SRC);
-			break;
-		case BPF_CMPXCHG:
-			BPF_R0 = (u32) atomic_cmpxchg(
-				(atomic_t *)(unsigned long) (DST + insn->off),
-				(u32) BPF_R0, (u32) SRC);
+#define ATOMIC(BOP, KOP)						\
+		case BOP:						\
+			if (BPF_SIZE(insn->code) == BPF_W)		\
+				atomic_##KOP((u32) SRC, (atomic_t *)(unsigned long) \
+					     (DST + insn->off));	\
+			else						\
+				atomic64_##KOP((u64) SRC, (atomic64_t *)(unsigned long) \
+					       (DST + insn->off));	\
+			break;						\
+		case BOP | BPF_FETCH:					\
+			if (BPF_SIZE(insn->code) == BPF_W)		\
+				SRC = (u32) atomic_fetch_##KOP(		\
+					(u32) SRC,			\
+					(atomic_t *)(unsigned long) (DST + insn->off)); \
+			else						\
+				SRC = (u64) atomic64_fetch_##KOP(	\
+					(u64) SRC,			\
+					(atomic64_t *)(s64) (DST + insn->off)); \
 			break;
-		default:
-			goto default_label;
-		}
-		CONT;
 
 	STX_ATOMIC_DW:
+	STX_ATOMIC_W:
 		switch (IMM) {
-		case BPF_ADD:
-			/* lock xadd *(u64 *)(dst_reg + off16) += src_reg */
-			atomic64_add((u64) SRC, (atomic64_t *)(unsigned long)
-				     (DST + insn->off));
-			break;
-		case BPF_ADD | BPF_FETCH:
-			SRC = (u64) atomic64_fetch_add(
-				(u64) SRC,
-				(atomic64_t *)(s64) (DST + insn->off));
-			break;
+		ATOMIC(BPF_ADD, add)
+
 		case BPF_XCHG:
-			SRC = (u64) atomic64_xchg(
-				(atomic64_t *)(u64) (DST + insn->off),
-				(u64) SRC);
+			if (BPF_SIZE(insn->code) == BPF_W)
+				SRC = (u32) atomic_xchg(
+					(atomic_t *)(unsigned long) (DST + insn->off),
+					(u32) SRC);
+			else
+				SRC = (u64) atomic64_xchg(
+					(atomic64_t *)(u64) (DST + insn->off),
+					(u64) SRC);
 			break;
 		case BPF_CMPXCHG:
-			BPF_R0 = (u64) atomic64_cmpxchg(
-				(atomic64_t *)(u64) (DST + insn->off),
-				(u64) BPF_R0, (u64) SRC);
+			if (BPF_SIZE(insn->code) == BPF_W)
+				BPF_R0 = (u32) atomic_cmpxchg(
+					(atomic_t *)(unsigned long) (DST + insn->off),
+					(u32) BPF_R0, (u32) SRC);
+			else
+				BPF_R0 = (u64) atomic64_cmpxchg(
+					(atomic64_t *)(u64) (DST + insn->off),
+					(u64) BPF_R0, (u64) SRC);
 			break;
+
 		default:
 			goto default_label;
 		}
-- 
2.29.2.454.gaff20da3a2-goog

[PATCH v2 bpf-next 10/13] bpf: Add instructions for atomic[64]_[fetch_]sub

[Brendan Jackman]

Including only interpreter and x86 JIT support.

x86 doesn't provide an atomic exchange-and-subtract instruction that
could be used for BPF_SUB | BPF_FETCH, however we can just emit a NEG
followed by an XADD to get the same effect.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 arch/x86/net/bpf_jit_comp.c  | 16 ++++++++++++++--
 include/linux/filter.h       | 20 ++++++++++++++++++++
 kernel/bpf/core.c            |  1 +
 kernel/bpf/disasm.c          | 16 ++++++++++++----
 kernel/bpf/verifier.c        |  2 ++
 tools/include/linux/filter.h | 20 ++++++++++++++++++++
 6 files changed, 69 insertions(+), 6 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 7431b2937157..a8a9fab13fcf 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -823,6 +823,7 @@ static int emit_atomic(u8 **pprog, u8 atomic_op,
 
 	/* emit opcode */
 	switch (atomic_op) {
+	case BPF_SUB:
 	case BPF_ADD:
 		/* lock *(u32/u64*)(dst_reg + off) <op>= src_reg */
 		EMIT1(simple_alu_opcodes[atomic_op]);
@@ -1306,8 +1307,19 @@ st:			if (is_imm8(insn->off))
 
 		case BPF_STX | BPF_ATOMIC | BPF_W:
 		case BPF_STX | BPF_ATOMIC | BPF_DW:
-			err = emit_atomic(&prog, insn->imm, dst_reg, src_reg,
-					  insn->off, BPF_SIZE(insn->code));
+			if (insn->imm == (BPF_SUB | BPF_FETCH)) {
+				/*
+				 * x86 doesn't have an XSUB insn, so we negate
+				 * and XADD instead.
+				 */
+				emit_neg(&prog, src_reg, BPF_SIZE(insn->code) == BPF_DW);
+				err = emit_atomic(&prog, BPF_ADD | BPF_FETCH,
+						  dst_reg, src_reg, insn->off,
+						  BPF_SIZE(insn->code));
+			} else {
+				err = emit_atomic(&prog, insn->imm, dst_reg, src_reg,
+						  insn->off, BPF_SIZE(insn->code));
+			}
 			if (err)
 				return err;
 			break;
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 6186280715ed..a20a3a536bf5 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -280,6 +280,26 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
 		.off   = OFF,					\
 		.imm   = BPF_ADD | BPF_FETCH })
 
+/* Atomic memory sub, *(uint *)(dst_reg + off16) -= src_reg */
+
+#define BPF_ATOMIC_SUB(SIZE, DST, SRC, OFF)			\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_SUB })
+
+/* Atomic memory sub with fetch, src_reg = atomic_fetch_sub(*(dst_reg + off), src_reg); */
+
+#define BPF_ATOMIC_FETCH_SUB(SIZE, DST, SRC, OFF)		\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_SUB | BPF_FETCH })
+
 /* Atomic exchange, src_reg = atomic_xchg((dst_reg + off), src_reg) */
 
 #define BPF_ATOMIC_XCHG(SIZE, DST, SRC, OFF)			\
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 20a5351d1dc2..0f700464955f 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1650,6 +1650,7 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
 	STX_ATOMIC_W:
 		switch (IMM) {
 		ATOMIC(BPF_ADD, add)
+		ATOMIC(BPF_SUB, sub)
 
 		case BPF_XCHG:
 			if (BPF_SIZE(insn->code) == BPF_W)
diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c
index 3441ac54ac65..f33acffdeed0 100644
--- a/kernel/bpf/disasm.c
+++ b/kernel/bpf/disasm.c
@@ -80,6 +80,11 @@ const char *const bpf_alu_string[16] = {
 	[BPF_END >> 4]  = "endian",
 };
 
+const char *const bpf_atomic_alu_string[16] = {
+	[BPF_ADD >> 4]  = "add",
+	[BPF_SUB >> 4]  = "sub",
+};
+
 static const char *const bpf_ldst_string[] = {
 	[BPF_W >> 3]  = "u32",
 	[BPF_H >> 3]  = "u16",
@@ -154,17 +159,20 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs,
 				insn->dst_reg,
 				insn->off, insn->src_reg);
 		else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
-			 insn->imm == BPF_ADD) {
-			verbose(cbs->private_data, "(%02x) lock *(%s *)(r%d %+d) += r%d\n",
+			 (insn->imm == BPF_ADD || insn->imm == BPF_SUB)) {
+			verbose(cbs->private_data, "(%02x) lock *(%s *)(r%d %+d) %s r%d\n",
 				insn->code,
 				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
 				insn->dst_reg, insn->off,
+				bpf_alu_string[BPF_OP(insn->imm) >> 4],
 				insn->src_reg);
 		} else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
-			   insn->imm == (BPF_ADD | BPF_FETCH)) {
-			verbose(cbs->private_data, "(%02x) r%d = atomic%s_fetch_add(*(%s *)(r%d %+d), r%d)\n",
+			   (insn->imm == (BPF_ADD | BPF_FETCH) ||
+			    insn->imm == (BPF_SUB | BPF_FETCH))) {
+			verbose(cbs->private_data, "(%02x) r%d = atomic%s_fetch_%s(*(%s *)(r%d %+d), r%d)\n",
 				insn->code, insn->src_reg,
 				BPF_SIZE(insn->code) == BPF_DW ? "64" : "",
+				bpf_atomic_alu_string[BPF_OP(insn->imm) >> 4],
 				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
 				insn->dst_reg, insn->off, insn->src_reg);
 		} else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c8311cc114ec..dea9ad486ad1 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3606,6 +3606,8 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
 	switch (insn->imm) {
 	case BPF_ADD:
 	case BPF_ADD | BPF_FETCH:
+	case BPF_SUB:
+	case BPF_SUB | BPF_FETCH:
 	case BPF_XCHG:
 	case BPF_CMPXCHG:
 		break;
diff --git a/tools/include/linux/filter.h b/tools/include/linux/filter.h
index ea99bd17d003..387eddaf11e5 100644
--- a/tools/include/linux/filter.h
+++ b/tools/include/linux/filter.h
@@ -190,6 +190,26 @@
 		.off   = OFF,					\
 		.imm   = BPF_ADD | BPF_FETCH })
 
+/* Atomic memory sub, *(uint *)(dst_reg + off16) -= src_reg */
+
+#define BPF_ATOMIC_SUB(SIZE, DST, SRC, OFF)			\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_SUB })
+
+/* Atomic memory sub with fetch, src_reg = atomic_fetch_sub(*(dst_reg + off), src_reg); */
+
+#define BPF_ATOMIC_FETCH_SUB(SIZE, DST, SRC, OFF)		\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_SUB | BPF_FETCH })
+
 /* Atomic exchange, src_reg = atomic_xchg((dst_reg + off), src_reg) */
 
 #define BPF_ATOMIC_XCHG(SIZE, DST, SRC, OFF)			\
-- 
2.29.2.454.gaff20da3a2-goog

Re: [PATCH v2 bpf-next 10/13] bpf: Add instructions for atomic[64]_[fetch_]sub

[kernel test robot]

[-- Attachment #1: Type: text/plain, Size: 1374 bytes --]

Hi Brendan,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on bpf-next/master]

url:    https://github.com/0day-ci/linux/commits/Brendan-Jackman/Atomics-for-eBPF/20201128-020057
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
config: i386-randconfig-s001-20201127 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-15) 9.3.0
reproduce:
        # apt-get install sparse
        # sparse version: v0.6.3-151-g540c2c4b-dirty
        # https://github.com/0day-ci/linux/commit/8b1823a5cf4569c72046175d217e3e2ad68c6a05
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Brendan-Jackman/Atomics-for-eBPF/20201128-020057
        git checkout 8b1823a5cf4569c72046175d217e3e2ad68c6a05
        # save the attached .config to linux build tree
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=i386 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>


"sparse warnings: (new ones prefixed by >>)"
>> kernel/bpf/disasm.c:83:12: sparse: sparse: symbol 'bpf_atomic_alu_string' was not declared. Should it be static?

Please review and possibly fold the followup patch.

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 33688 bytes --]

[RFC PATCH] bpf: bpf_atomic_alu_string[] can be static

[kernel test robot]

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: kernel test robot <lkp@intel.com>
---
 disasm.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c
index f33acffdeed05..737e95b049574 100644
--- a/kernel/bpf/disasm.c
+++ b/kernel/bpf/disasm.c
@@ -80,7 +80,7 @@ const char *const bpf_alu_string[16] = {
 	[BPF_END >> 4]  = "endian",
 };
 
-const char *const bpf_atomic_alu_string[16] = {
+static const char *const bpf_atomic_alu_string[16] = {
 	[BPF_ADD >> 4]  = "add",
 	[BPF_SUB >> 4]  = "sub",
 };

Re: [PATCH v2 bpf-next 10/13] bpf: Add instructions for atomic[64]_[fetch_]sub

[Yonghong Song]

On 11/27/20 9:57 AM, Brendan Jackman wrote:
> Including only interpreter and x86 JIT support.
> 
> x86 doesn't provide an atomic exchange-and-subtract instruction that
> could be used for BPF_SUB | BPF_FETCH, however we can just emit a NEG
> followed by an XADD to get the same effect.
> 
> Signed-off-by: Brendan Jackman <jackmanb@google.com>
> ---
>   arch/x86/net/bpf_jit_comp.c  | 16 ++++++++++++++--
>   include/linux/filter.h       | 20 ++++++++++++++++++++
>   kernel/bpf/core.c            |  1 +
>   kernel/bpf/disasm.c          | 16 ++++++++++++----
>   kernel/bpf/verifier.c        |  2 ++
>   tools/include/linux/filter.h | 20 ++++++++++++++++++++
>   6 files changed, 69 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 7431b2937157..a8a9fab13fcf 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -823,6 +823,7 @@ static int emit_atomic(u8 **pprog, u8 atomic_op,
>   
>   	/* emit opcode */
>   	switch (atomic_op) {
> +	case BPF_SUB:
>   	case BPF_ADD:
>   		/* lock *(u32/u64*)(dst_reg + off) <op>= src_reg */
>   		EMIT1(simple_alu_opcodes[atomic_op]);
> @@ -1306,8 +1307,19 @@ st:			if (is_imm8(insn->off))
>   
>   		case BPF_STX | BPF_ATOMIC | BPF_W:
>   		case BPF_STX | BPF_ATOMIC | BPF_DW:
> -			err = emit_atomic(&prog, insn->imm, dst_reg, src_reg,
> -					  insn->off, BPF_SIZE(insn->code));
> +			if (insn->imm == (BPF_SUB | BPF_FETCH)) {
> +				/*
> +				 * x86 doesn't have an XSUB insn, so we negate
> +				 * and XADD instead.
> +				 */
> +				emit_neg(&prog, src_reg, BPF_SIZE(insn->code) == BPF_DW);
> +				err = emit_atomic(&prog, BPF_ADD | BPF_FETCH,
> +						  dst_reg, src_reg, insn->off,
> +						  BPF_SIZE(insn->code));
> +			} else {
> +				err = emit_atomic(&prog, insn->imm, dst_reg, src_reg,
> +						  insn->off, BPF_SIZE(insn->code));
> +			}
>   			if (err)
>   				return err;
>   			break;
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 6186280715ed..a20a3a536bf5 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -280,6 +280,26 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
>   		.off   = OFF,					\
>   		.imm   = BPF_ADD | BPF_FETCH })
>   
> +/* Atomic memory sub, *(uint *)(dst_reg + off16) -= src_reg */
> +
> +#define BPF_ATOMIC_SUB(SIZE, DST, SRC, OFF)			\
> +	((struct bpf_insn) {					\
> +		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
> +		.dst_reg = DST,					\
> +		.src_reg = SRC,					\
> +		.off   = OFF,					\
> +		.imm   = BPF_SUB })

Currently, llvm does not support XSUB, should we support it in llvm?
At source code, as implemented in JIT, user can just do a negate
followed by xadd.

> +
> +/* Atomic memory sub with fetch, src_reg = atomic_fetch_sub(*(dst_reg + off), src_reg); */
> +
> +#define BPF_ATOMIC_FETCH_SUB(SIZE, DST, SRC, OFF)		\
> +	((struct bpf_insn) {					\
> +		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
> +		.dst_reg = DST,					\
> +		.src_reg = SRC,					\
> +		.off   = OFF,					\
> +		.imm   = BPF_SUB | BPF_FETCH })
> +
>   /* Atomic exchange, src_reg = atomic_xchg((dst_reg + off), src_reg) */
>   
>   #define BPF_ATOMIC_XCHG(SIZE, DST, SRC, OFF)			\
[...]

Re: [PATCH v2 bpf-next 10/13] bpf: Add instructions for atomic[64]_[fetch_]sub

[Alexei Starovoitov]

On Fri, Nov 27, 2020 at 09:35:07PM -0800, Yonghong Song wrote:
> 
> 
> On 11/27/20 9:57 AM, Brendan Jackman wrote:
> > Including only interpreter and x86 JIT support.
> > 
> > x86 doesn't provide an atomic exchange-and-subtract instruction that
> > could be used for BPF_SUB | BPF_FETCH, however we can just emit a NEG
> > followed by an XADD to get the same effect.
> > 
> > Signed-off-by: Brendan Jackman <jackmanb@google.com>
> > ---
> >   arch/x86/net/bpf_jit_comp.c  | 16 ++++++++++++++--
> >   include/linux/filter.h       | 20 ++++++++++++++++++++
> >   kernel/bpf/core.c            |  1 +
> >   kernel/bpf/disasm.c          | 16 ++++++++++++----
> >   kernel/bpf/verifier.c        |  2 ++
> >   tools/include/linux/filter.h | 20 ++++++++++++++++++++
> >   6 files changed, 69 insertions(+), 6 deletions(-)
> > 
> > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> > index 7431b2937157..a8a9fab13fcf 100644
> > --- a/arch/x86/net/bpf_jit_comp.c
> > +++ b/arch/x86/net/bpf_jit_comp.c
> > @@ -823,6 +823,7 @@ static int emit_atomic(u8 **pprog, u8 atomic_op,
> >   	/* emit opcode */
> >   	switch (atomic_op) {
> > +	case BPF_SUB:
> >   	case BPF_ADD:
> >   		/* lock *(u32/u64*)(dst_reg + off) <op>= src_reg */
> >   		EMIT1(simple_alu_opcodes[atomic_op]);
> > @@ -1306,8 +1307,19 @@ st:			if (is_imm8(insn->off))
> >   		case BPF_STX | BPF_ATOMIC | BPF_W:
> >   		case BPF_STX | BPF_ATOMIC | BPF_DW:
> > -			err = emit_atomic(&prog, insn->imm, dst_reg, src_reg,
> > -					  insn->off, BPF_SIZE(insn->code));
> > +			if (insn->imm == (BPF_SUB | BPF_FETCH)) {
> > +				/*
> > +				 * x86 doesn't have an XSUB insn, so we negate
> > +				 * and XADD instead.
> > +				 */
> > +				emit_neg(&prog, src_reg, BPF_SIZE(insn->code) == BPF_DW);
> > +				err = emit_atomic(&prog, BPF_ADD | BPF_FETCH,
> > +						  dst_reg, src_reg, insn->off,
> > +						  BPF_SIZE(insn->code));
> > +			} else {
> > +				err = emit_atomic(&prog, insn->imm, dst_reg, src_reg,
> > +						  insn->off, BPF_SIZE(insn->code));
> > +			}
> >   			if (err)
> >   				return err;
> >   			break;
> > diff --git a/include/linux/filter.h b/include/linux/filter.h
> > index 6186280715ed..a20a3a536bf5 100644
> > --- a/include/linux/filter.h
> > +++ b/include/linux/filter.h
> > @@ -280,6 +280,26 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
> >   		.off   = OFF,					\
> >   		.imm   = BPF_ADD | BPF_FETCH })
> > +/* Atomic memory sub, *(uint *)(dst_reg + off16) -= src_reg */
> > +
> > +#define BPF_ATOMIC_SUB(SIZE, DST, SRC, OFF)			\
> > +	((struct bpf_insn) {					\
> > +		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
> > +		.dst_reg = DST,					\
> > +		.src_reg = SRC,					\
> > +		.off   = OFF,					\
> > +		.imm   = BPF_SUB })
> 
> Currently, llvm does not support XSUB, should we support it in llvm?
> At source code, as implemented in JIT, user can just do a negate
> followed by xadd.

I forgot we have BPF_NEG insn :)
Indeed it's probably easier to handle atomic_fetch_sub() builtin
completely on llvm side. It can generate bpf_neg followed by atomic_fetch_add.
No need to burden verifier, interpreter and JITs with it.

Re: [PATCH v2 bpf-next 10/13] bpf: Add instructions for atomic[64]_[fetch_]sub

[Yonghong Song]

On 11/28/20 5:34 PM, Alexei Starovoitov wrote:
> On Fri, Nov 27, 2020 at 09:35:07PM -0800, Yonghong Song wrote:
>>
>>
>> On 11/27/20 9:57 AM, Brendan Jackman wrote:
>>> Including only interpreter and x86 JIT support.
>>>
>>> x86 doesn't provide an atomic exchange-and-subtract instruction that
>>> could be used for BPF_SUB | BPF_FETCH, however we can just emit a NEG
>>> followed by an XADD to get the same effect.
>>>
>>> Signed-off-by: Brendan Jackman <jackmanb@google.com>
>>> ---
>>>    arch/x86/net/bpf_jit_comp.c  | 16 ++++++++++++++--
>>>    include/linux/filter.h       | 20 ++++++++++++++++++++
>>>    kernel/bpf/core.c            |  1 +
>>>    kernel/bpf/disasm.c          | 16 ++++++++++++----
>>>    kernel/bpf/verifier.c        |  2 ++
>>>    tools/include/linux/filter.h | 20 ++++++++++++++++++++
>>>    6 files changed, 69 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
>>> index 7431b2937157..a8a9fab13fcf 100644
>>> --- a/arch/x86/net/bpf_jit_comp.c
>>> +++ b/arch/x86/net/bpf_jit_comp.c
>>> @@ -823,6 +823,7 @@ static int emit_atomic(u8 **pprog, u8 atomic_op,
>>>    	/* emit opcode */
>>>    	switch (atomic_op) {
>>> +	case BPF_SUB:
>>>    	case BPF_ADD:
>>>    		/* lock *(u32/u64*)(dst_reg + off) <op>= src_reg */
>>>    		EMIT1(simple_alu_opcodes[atomic_op]);
>>> @@ -1306,8 +1307,19 @@ st:			if (is_imm8(insn->off))
>>>    		case BPF_STX | BPF_ATOMIC | BPF_W:
>>>    		case BPF_STX | BPF_ATOMIC | BPF_DW:
>>> -			err = emit_atomic(&prog, insn->imm, dst_reg, src_reg,
>>> -					  insn->off, BPF_SIZE(insn->code));
>>> +			if (insn->imm == (BPF_SUB | BPF_FETCH)) {
>>> +				/*
>>> +				 * x86 doesn't have an XSUB insn, so we negate
>>> +				 * and XADD instead.
>>> +				 */
>>> +				emit_neg(&prog, src_reg, BPF_SIZE(insn->code) == BPF_DW);
>>> +				err = emit_atomic(&prog, BPF_ADD | BPF_FETCH,
>>> +						  dst_reg, src_reg, insn->off,
>>> +						  BPF_SIZE(insn->code));
>>> +			} else {
>>> +				err = emit_atomic(&prog, insn->imm, dst_reg, src_reg,
>>> +						  insn->off, BPF_SIZE(insn->code));
>>> +			}
>>>    			if (err)
>>>    				return err;
>>>    			break;
>>> diff --git a/include/linux/filter.h b/include/linux/filter.h
>>> index 6186280715ed..a20a3a536bf5 100644
>>> --- a/include/linux/filter.h
>>> +++ b/include/linux/filter.h
>>> @@ -280,6 +280,26 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
>>>    		.off   = OFF,					\
>>>    		.imm   = BPF_ADD | BPF_FETCH })
>>> +/* Atomic memory sub, *(uint *)(dst_reg + off16) -= src_reg */
>>> +
>>> +#define BPF_ATOMIC_SUB(SIZE, DST, SRC, OFF)			\
>>> +	((struct bpf_insn) {					\
>>> +		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
>>> +		.dst_reg = DST,					\
>>> +		.src_reg = SRC,					\
>>> +		.off   = OFF,					\
>>> +		.imm   = BPF_SUB })
>>
>> Currently, llvm does not support XSUB, should we support it in llvm?
>> At source code, as implemented in JIT, user can just do a negate
>> followed by xadd.
> 
> I forgot we have BPF_NEG insn :)
> Indeed it's probably easier to handle atomic_fetch_sub() builtin
> completely on llvm side. It can generate bpf_neg followed by atomic_fetch_add.

Just tried. llvm selectiondag won't be able to automatically
convert atomic_fetch_sub to neg + atomic_fetch_add. So there
will be a need in BPFInstrInfo.td to match atomic_fetch_sub IR
pattern. I will experiment this together with xsub.

> No need to burden verifier, interpreter and JITs with it.
> 

Re: [PATCH v2 bpf-next 10/13] bpf: Add instructions for atomic[64]_[fetch_]sub

[Brendan Jackman]

On Mon, Nov 30, 2020 at 09:18:09AM -0800, Yonghong Song wrote:
> On 11/28/20 5:34 PM, Alexei Starovoitov wrote:
> > On Fri, Nov 27, 2020 at 09:35:07PM -0800, Yonghong Song wrote:
> > > On 11/27/20 9:57 AM, Brendan Jackman wrote:
[...]
> > > > +#define BPF_ATOMIC_SUB(SIZE, DST, SRC, OFF)			\
> > > > +	((struct bpf_insn) {					\
> > > > +		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
> > > > +		.dst_reg = DST,					\
> > > > +		.src_reg = SRC,					\
> > > > +		.off   = OFF,					\
> > > > +		.imm   = BPF_SUB })
> > > 
> > > Currently, llvm does not support XSUB, should we support it in llvm?
> > > At source code, as implemented in JIT, user can just do a negate
> > > followed by xadd.
> > 
> > I forgot we have BPF_NEG insn :)
> > Indeed it's probably easier to handle atomic_fetch_sub() builtin
> > completely on llvm side. It can generate bpf_neg followed by atomic_fetch_add.
> 
> Just tried. llvm selectiondag won't be able to automatically
> convert atomic_fetch_sub to neg + atomic_fetch_add. So there
> will be a need in BPFInstrInfo.td to match atomic_fetch_sub IR
> pattern. I will experiment this together with xsub.
> 
> > No need to burden verifier, interpreter and JITs with it.
> > 

I guess it's also worth remembering other archs might have an atomic
subtract.

Re: [PATCH v2 bpf-next 10/13] bpf: Add instructions for atomic[64]_[fetch_]sub

[Alexei Starovoitov]

On Tue, Dec 1, 2020 at 4:38 AM Brendan Jackman <jackmanb@google.com> wrote:
>
> I guess it's also worth remembering other archs might have an atomic
> subtract.

which one?
arm64 LSE implements atomic_fetch_sub as neg+ldadd.
imo x64 and arm64 example outweighs choices by other archs if there are such.
Even without LSE it will be neg+llsc loop.
The reason I proposed bpf xsub insn earlier is that I thought that llvm
won't be able to emit it so easily and JIT/verifier would struggle.

Re: [PATCH v2 bpf-next 10/13] bpf: Add instructions for atomic[64]_[fetch_]sub

[Brendan Jackman]

On Tue, Dec 01, 2020 at 09:55:22PM -0800, Alexei Starovoitov wrote:
> On Tue, Dec 1, 2020 at 4:38 AM Brendan Jackman <jackmanb@google.com> wrote:
> >
> > I guess it's also worth remembering other archs might have an atomic
> > subtract.
> 
> which one?
> arm64 LSE implements atomic_fetch_sub as neg+ldadd.
> imo x64 and arm64 example outweighs choices by other archs if there are such.
> Even without LSE it will be neg+llsc loop.
> The reason I proposed bpf xsub insn earlier is that I thought that llvm
> won't be able to emit it so easily and JIT/verifier would struggle.

Ack, I'll drop the atomic subtract instruction.

[PATCH v2 bpf-next 11/13] bpf: Add bitwise atomic instructions

[Brendan Jackman]

This adds instructions for

atomic[64]_[fetch_]and
atomic[64]_[fetch_]or
atomic[64]_[fetch_]xor

All these operations are isomorphic enough to implement with the same
verifier, interpreter, and x86 JIT code, hence being a single commit.

The main interesting thing here is that x86 doesn't directly support
the fetch_ version these operations, so we need to generate a CMPXCHG
loop in the JIT. This requires the use of two temporary registers,
IIUC it's safe to use BPF_REG_AX and x86's AUX_REG for this purpose.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 arch/x86/net/bpf_jit_comp.c  | 49 ++++++++++++++++++++++++++++-
 include/linux/filter.h       | 60 ++++++++++++++++++++++++++++++++++++
 kernel/bpf/core.c            |  5 ++-
 kernel/bpf/disasm.c          |  7 +++--
 kernel/bpf/verifier.c        |  6 ++++
 tools/include/linux/filter.h | 60 ++++++++++++++++++++++++++++++++++++
 6 files changed, 183 insertions(+), 4 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index a8a9fab13fcf..46b977ee21c4 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -823,8 +823,11 @@ static int emit_atomic(u8 **pprog, u8 atomic_op,
 
 	/* emit opcode */
 	switch (atomic_op) {
-	case BPF_SUB:
 	case BPF_ADD:
+	case BPF_SUB:
+	case BPF_AND:
+	case BPF_OR:
+	case BPF_XOR:
 		/* lock *(u32/u64*)(dst_reg + off) <op>= src_reg */
 		EMIT1(simple_alu_opcodes[atomic_op]);
 		break;
@@ -1307,6 +1310,50 @@ st:			if (is_imm8(insn->off))
 
 		case BPF_STX | BPF_ATOMIC | BPF_W:
 		case BPF_STX | BPF_ATOMIC | BPF_DW:
+			if (insn->imm == (BPF_AND | BPF_FETCH) ||
+			    insn->imm == (BPF_OR | BPF_FETCH) ||
+			    insn->imm == (BPF_XOR | BPF_FETCH)) {
+				u8 *branch_target;
+				bool is64 = BPF_SIZE(insn->code) == BPF_DW;
+
+				/*
+				 * Can't be implemented with a single x86 insn.
+				 * Need to do a CMPXCHG loop.
+				 */
+
+				/* Will need RAX as a CMPXCHG operand so save R0 */
+				emit_mov_reg(&prog, true, BPF_REG_AX, BPF_REG_0);
+				branch_target = prog;
+				/* Load old value */
+				emit_ldx(&prog, BPF_SIZE(insn->code),
+					 BPF_REG_0, dst_reg, insn->off);
+				/*
+				 * Perform the (commutative) operation locally,
+				 * put the result in the AUX_REG.
+				 */
+				emit_mov_reg(&prog, is64, AUX_REG, BPF_REG_0);
+				maybe_emit_rex(&prog, AUX_REG, src_reg, is64);
+				EMIT2(simple_alu_opcodes[BPF_OP(insn->imm)],
+				      add_2reg(0xC0, AUX_REG, src_reg));
+				/* Attempt to swap in new value */
+				err = emit_atomic(&prog, BPF_CMPXCHG,
+						  dst_reg, AUX_REG, insn->off,
+						  BPF_SIZE(insn->code));
+				if (WARN_ON(err))
+					return err;
+				/*
+				 * ZF tells us whether we won the race. If it's
+				 * cleared we need to try again.
+				 */
+				EMIT2(X86_JNE, -(prog - branch_target) - 2);
+				/* Return the pre-modification value */
+				emit_mov_reg(&prog, is64, src_reg, BPF_REG_0);
+				/* Restore R0 after clobbering RAX */
+				emit_mov_reg(&prog, true, BPF_REG_0, BPF_REG_AX);
+				break;
+
+			}
+
 			if (insn->imm == (BPF_SUB | BPF_FETCH)) {
 				/*
 				 * x86 doesn't have an XSUB insn, so we negate
diff --git a/include/linux/filter.h b/include/linux/filter.h
index a20a3a536bf5..cb5d865cce3c 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -300,6 +300,66 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
 		.off   = OFF,					\
 		.imm   = BPF_SUB | BPF_FETCH })
 
+/* Atomic memory and, *(uint *)(dst_reg + off16) -= src_reg */
+
+#define BPF_ATOMIC_AND(SIZE, DST, SRC, OFF)			\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_AND })
+
+/* Atomic memory and with fetch, src_reg = atomic_fetch_and(*(dst_reg + off), src_reg); */
+
+#define BPF_ATOMIC_FETCH_AND(SIZE, DST, SRC, OFF)		\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_AND | BPF_FETCH })
+
+/* Atomic memory or, *(uint *)(dst_reg + off16) -= src_reg */
+
+#define BPF_ATOMIC_OR(SIZE, DST, SRC, OFF)			\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_OR })
+
+/* Atomic memory or with fetch, src_reg = atomic_fetch_or(*(dst_reg + off), src_reg); */
+
+#define BPF_ATOMIC_FETCH_OR(SIZE, DST, SRC, OFF)		\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_OR | BPF_FETCH })
+
+/* Atomic memory xor, *(uint *)(dst_reg + off16) -= src_reg */
+
+#define BPF_ATOMIC_XOR(SIZE, DST, SRC, OFF)			\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_XOR })
+
+/* Atomic memory xor with fetch, src_reg = atomic_fetch_xor(*(dst_reg + off), src_reg); */
+
+#define BPF_ATOMIC_FETCH_XOR(SIZE, DST, SRC, OFF)		\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_XOR | BPF_FETCH })
+
 /* Atomic exchange, src_reg = atomic_xchg((dst_reg + off), src_reg) */
 
 #define BPF_ATOMIC_XCHG(SIZE, DST, SRC, OFF)			\
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 0f700464955f..d5f4b1f2c9fe 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1651,7 +1651,10 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
 		switch (IMM) {
 		ATOMIC(BPF_ADD, add)
 		ATOMIC(BPF_SUB, sub)
-
+		ATOMIC(BPF_AND, and)
+		ATOMIC(BPF_OR, or)
+		ATOMIC(BPF_XOR, xor)
+#undef ATOMIC
 		case BPF_XCHG:
 			if (BPF_SIZE(insn->code) == BPF_W)
 				SRC = (u32) atomic_xchg(
diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c
index f33acffdeed0..4c861632efac 100644
--- a/kernel/bpf/disasm.c
+++ b/kernel/bpf/disasm.c
@@ -83,6 +83,7 @@ const char *const bpf_alu_string[16] = {
 const char *const bpf_atomic_alu_string[16] = {
 	[BPF_ADD >> 4]  = "add",
 	[BPF_SUB >> 4]  = "sub",
+	[BPF_AND >> 4]  = "and",
 };
 
 static const char *const bpf_ldst_string[] = {
@@ -159,7 +160,8 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs,
 				insn->dst_reg,
 				insn->off, insn->src_reg);
 		else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
-			 (insn->imm == BPF_ADD || insn->imm == BPF_SUB)) {
+			 (insn->imm == BPF_ADD || insn->imm == BPF_SUB ||
+			  (insn->imm == BPF_AND))) {
 			verbose(cbs->private_data, "(%02x) lock *(%s *)(r%d %+d) %s r%d\n",
 				insn->code,
 				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
@@ -168,7 +170,8 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs,
 				insn->src_reg);
 		} else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
 			   (insn->imm == (BPF_ADD | BPF_FETCH) ||
-			    insn->imm == (BPF_SUB | BPF_FETCH))) {
+			    insn->imm == (BPF_SUB | BPF_FETCH) ||
+			    insn->imm == (BPF_AND | BPF_FETCH))) {
 			verbose(cbs->private_data, "(%02x) r%d = atomic%s_fetch_%s(*(%s *)(r%d %+d), r%d)\n",
 				insn->code, insn->src_reg,
 				BPF_SIZE(insn->code) == BPF_DW ? "64" : "",
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index dea9ad486ad1..188f152a0c32 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3608,6 +3608,12 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
 	case BPF_ADD | BPF_FETCH:
 	case BPF_SUB:
 	case BPF_SUB | BPF_FETCH:
+	case BPF_AND:
+	case BPF_AND | BPF_FETCH:
+	case BPF_OR:
+	case BPF_OR | BPF_FETCH:
+	case BPF_XOR:
+	case BPF_XOR | BPF_FETCH:
 	case BPF_XCHG:
 	case BPF_CMPXCHG:
 		break;
diff --git a/tools/include/linux/filter.h b/tools/include/linux/filter.h
index 387eddaf11e5..2a64149af056 100644
--- a/tools/include/linux/filter.h
+++ b/tools/include/linux/filter.h
@@ -210,6 +210,66 @@
 		.off   = OFF,					\
 		.imm   = BPF_SUB | BPF_FETCH })
 
+/* Atomic memory and, *(uint *)(dst_reg + off16) -= src_reg */
+
+#define BPF_ATOMIC_AND(SIZE, DST, SRC, OFF)			\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_AND })
+
+/* Atomic memory and with fetch, src_reg = atomic_fetch_and(*(dst_reg + off), src_reg); */
+
+#define BPF_ATOMIC_FETCH_AND(SIZE, DST, SRC, OFF)		\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_AND | BPF_FETCH })
+
+/* Atomic memory or, *(uint *)(dst_reg + off16) -= src_reg */
+
+#define BPF_ATOMIC_OR(SIZE, DST, SRC, OFF)			\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_OR })
+
+/* Atomic memory or with fetch, src_reg = atomic_fetch_or(*(dst_reg + off), src_reg); */
+
+#define BPF_ATOMIC_FETCH_OR(SIZE, DST, SRC, OFF)		\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_OR | BPF_FETCH })
+
+/* Atomic memory xor, *(uint *)(dst_reg + off16) -= src_reg */
+
+#define BPF_ATOMIC_XOR(SIZE, DST, SRC, OFF)			\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_XOR })
+
+/* Atomic memory xor with fetch, src_reg = atomic_fetch_xor(*(dst_reg + off), src_reg); */
+
+#define BPF_ATOMIC_FETCH_XOR(SIZE, DST, SRC, OFF)		\
+	((struct bpf_insn) {					\
+		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
+		.dst_reg = DST,					\
+		.src_reg = SRC,					\
+		.off   = OFF,					\
+		.imm   = BPF_XOR | BPF_FETCH })
+
 /* Atomic exchange, src_reg = atomic_xchg((dst_reg + off), src_reg) */
 
 #define BPF_ATOMIC_XCHG(SIZE, DST, SRC, OFF)			\
-- 
2.29.2.454.gaff20da3a2-goog

Re: [PATCH v2 bpf-next 11/13] bpf: Add bitwise atomic instructions

[Yonghong Song]

On 11/27/20 9:57 AM, Brendan Jackman wrote:
> This adds instructions for
> 
> atomic[64]_[fetch_]and
> atomic[64]_[fetch_]or
> atomic[64]_[fetch_]xor
> 
> All these operations are isomorphic enough to implement with the same
> verifier, interpreter, and x86 JIT code, hence being a single commit.
> 
> The main interesting thing here is that x86 doesn't directly support
> the fetch_ version these operations, so we need to generate a CMPXCHG
> loop in the JIT. This requires the use of two temporary registers,
> IIUC it's safe to use BPF_REG_AX and x86's AUX_REG for this purpose.

similar to previous xsub (atomic[64]_sub), should we implement
xand, xor, xxor in llvm?

> 
> Signed-off-by: Brendan Jackman <jackmanb@google.com>
> ---
>   arch/x86/net/bpf_jit_comp.c  | 49 ++++++++++++++++++++++++++++-
>   include/linux/filter.h       | 60 ++++++++++++++++++++++++++++++++++++
>   kernel/bpf/core.c            |  5 ++-
>   kernel/bpf/disasm.c          |  7 +++--
>   kernel/bpf/verifier.c        |  6 ++++
>   tools/include/linux/filter.h | 60 ++++++++++++++++++++++++++++++++++++
>   6 files changed, 183 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index a8a9fab13fcf..46b977ee21c4 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -823,8 +823,11 @@ static int emit_atomic(u8 **pprog, u8 atomic_op,
>   
>   	/* emit opcode */
>   	switch (atomic_op) {
> -	case BPF_SUB:
>   	case BPF_ADD:
> +	case BPF_SUB:
> +	case BPF_AND:
> +	case BPF_OR:
> +	case BPF_XOR:
>   		/* lock *(u32/u64*)(dst_reg + off) <op>= src_reg */
>   		EMIT1(simple_alu_opcodes[atomic_op]);
>   		break;
> @@ -1307,6 +1310,50 @@ st:			if (is_imm8(insn->off))
>   
>   		case BPF_STX | BPF_ATOMIC | BPF_W:
>   		case BPF_STX | BPF_ATOMIC | BPF_DW:
> +			if (insn->imm == (BPF_AND | BPF_FETCH) ||
> +			    insn->imm == (BPF_OR | BPF_FETCH) ||
> +			    insn->imm == (BPF_XOR | BPF_FETCH)) {
> +				u8 *branch_target;
> +				bool is64 = BPF_SIZE(insn->code) == BPF_DW;
> +
> +				/*
> +				 * Can't be implemented with a single x86 insn.
> +				 * Need to do a CMPXCHG loop.
> +				 */
> +
> +				/* Will need RAX as a CMPXCHG operand so save R0 */
> +				emit_mov_reg(&prog, true, BPF_REG_AX, BPF_REG_0);
> +				branch_target = prog;
> +				/* Load old value */
> +				emit_ldx(&prog, BPF_SIZE(insn->code),
> +					 BPF_REG_0, dst_reg, insn->off);
> +				/*
> +				 * Perform the (commutative) operation locally,
> +				 * put the result in the AUX_REG.
> +				 */
> +				emit_mov_reg(&prog, is64, AUX_REG, BPF_REG_0);
> +				maybe_emit_rex(&prog, AUX_REG, src_reg, is64);
> +				EMIT2(simple_alu_opcodes[BPF_OP(insn->imm)],
> +				      add_2reg(0xC0, AUX_REG, src_reg));
> +				/* Attempt to swap in new value */
> +				err = emit_atomic(&prog, BPF_CMPXCHG,
> +						  dst_reg, AUX_REG, insn->off,
> +						  BPF_SIZE(insn->code));
> +				if (WARN_ON(err))
> +					return err;
> +				/*
> +				 * ZF tells us whether we won the race. If it's
> +				 * cleared we need to try again.
> +				 */
> +				EMIT2(X86_JNE, -(prog - branch_target) - 2);
> +				/* Return the pre-modification value */
> +				emit_mov_reg(&prog, is64, src_reg, BPF_REG_0);
> +				/* Restore R0 after clobbering RAX */
> +				emit_mov_reg(&prog, true, BPF_REG_0, BPF_REG_AX);
> +				break;
> +
> +			}
> +
>   			if (insn->imm == (BPF_SUB | BPF_FETCH)) {
>   				/*
>   				 * x86 doesn't have an XSUB insn, so we negate
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index a20a3a536bf5..cb5d865cce3c 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -300,6 +300,66 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
>   		.off   = OFF,					\
>   		.imm   = BPF_SUB | BPF_FETCH })
>   
> +/* Atomic memory and, *(uint *)(dst_reg + off16) -= src_reg */
> +
> +#define BPF_ATOMIC_AND(SIZE, DST, SRC, OFF)			\
> +	((struct bpf_insn) {					\
> +		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
> +		.dst_reg = DST,					\
> +		.src_reg = SRC,					\
> +		.off   = OFF,					\
> +		.imm   = BPF_AND })
> +
> +/* Atomic memory and with fetch, src_reg = atomic_fetch_and(*(dst_reg + off), src_reg); */
> +
> +#define BPF_ATOMIC_FETCH_AND(SIZE, DST, SRC, OFF)		\
> +	((struct bpf_insn) {					\
> +		.code  = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC,	\
> +		.dst_reg = DST,					\
> +		.src_reg = SRC,					\
> +		.off   = OFF,					\
> +		.imm   = BPF_AND | BPF_FETCH })
> +
[...]

Re: [PATCH v2 bpf-next 11/13] bpf: Add bitwise atomic instructions

[Alexei Starovoitov]

On Fri, Nov 27, 2020 at 09:39:10PM -0800, Yonghong Song wrote:
> 
> 
> On 11/27/20 9:57 AM, Brendan Jackman wrote:
> > This adds instructions for
> > 
> > atomic[64]_[fetch_]and
> > atomic[64]_[fetch_]or
> > atomic[64]_[fetch_]xor
> > 
> > All these operations are isomorphic enough to implement with the same
> > verifier, interpreter, and x86 JIT code, hence being a single commit.
> > 
> > The main interesting thing here is that x86 doesn't directly support
> > the fetch_ version these operations, so we need to generate a CMPXCHG
> > loop in the JIT. This requires the use of two temporary registers,
> > IIUC it's safe to use BPF_REG_AX and x86's AUX_REG for this purpose.
> 
> similar to previous xsub (atomic[64]_sub), should we implement
> xand, xor, xxor in llvm?

yes. please. Unlike atomic_fetch_sub that can be handled by llvm.
atomic_fetch_or/xor/and has to be seen as separate instructions
because JITs will translate them as loop.

Re: [PATCH v2 bpf-next 11/13] bpf: Add bitwise atomic instructions

[Yonghong Song]

On 11/28/20 5:36 PM, Alexei Starovoitov wrote:
> On Fri, Nov 27, 2020 at 09:39:10PM -0800, Yonghong Song wrote:
>>
>>
>> On 11/27/20 9:57 AM, Brendan Jackman wrote:
>>> This adds instructions for
>>>
>>> atomic[64]_[fetch_]and
>>> atomic[64]_[fetch_]or
>>> atomic[64]_[fetch_]xor
>>>
>>> All these operations are isomorphic enough to implement with the same
>>> verifier, interpreter, and x86 JIT code, hence being a single commit.
>>>
>>> The main interesting thing here is that x86 doesn't directly support
>>> the fetch_ version these operations, so we need to generate a CMPXCHG
>>> loop in the JIT. This requires the use of two temporary registers,
>>> IIUC it's safe to use BPF_REG_AX and x86's AUX_REG for this purpose.
>>
>> similar to previous xsub (atomic[64]_sub), should we implement
>> xand, xor, xxor in llvm?
> 
> yes. please. Unlike atomic_fetch_sub that can be handled by llvm.
> atomic_fetch_or/xor/and has to be seen as separate instructions
> because JITs will translate them as loop.

Okay, will try to implement xsub, xand, xor and xxor in llvm.

[PATCH v2 bpf-next 12/13] bpf: Add tests for new BPF atomic operations

[Brendan Jackman]

This relies on the work done by Yonghong Song in
https://reviews.llvm.org/D72184

Note the hackery in the Makefile that is necessary to avoid breaking
tests for people who haven't yet got a version of Clang supporting
V4. It seems like this hackery ought to be confined to
tools/build/feature - I tried implementing that and found that it
ballooned into an explosion of nightmares at the top of
tools/testing/selftests/bpf/Makefile without actually improving the
clarity of the CLANG_BPF_BUILD_RULE code at all. Hence the simple
$(shell) call...

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 tools/testing/selftests/bpf/Makefile          |  12 +-
 .../selftests/bpf/prog_tests/atomics_test.c   | 329 ++++++++++++++++++
 .../selftests/bpf/progs/atomics_test.c        | 124 +++++++
 .../selftests/bpf/verifier/atomic_and.c       |  77 ++++
 .../selftests/bpf/verifier/atomic_cmpxchg.c   |  96 +++++
 .../selftests/bpf/verifier/atomic_fetch_add.c | 106 ++++++
 .../selftests/bpf/verifier/atomic_or.c        |  77 ++++
 .../selftests/bpf/verifier/atomic_sub.c       |  44 +++
 .../selftests/bpf/verifier/atomic_xchg.c      |  46 +++
 .../selftests/bpf/verifier/atomic_xor.c       |  77 ++++
 tools/testing/selftests/bpf/verifier/ctx.c    |   2 +-
 11 files changed, 987 insertions(+), 3 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/atomics_test.c
 create mode 100644 tools/testing/selftests/bpf/progs/atomics_test.c
 create mode 100644 tools/testing/selftests/bpf/verifier/atomic_and.c
 create mode 100644 tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c
 create mode 100644 tools/testing/selftests/bpf/verifier/atomic_fetch_add.c
 create mode 100644 tools/testing/selftests/bpf/verifier/atomic_or.c
 create mode 100644 tools/testing/selftests/bpf/verifier/atomic_sub.c
 create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xchg.c
 create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xor.c

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 3d5940cd110d..5eadfd09037d 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -228,6 +228,12 @@ IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null | \
 			grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
 MENDIAN=$(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
 
+# Determine if Clang supports BPF arch v4, and therefore atomics.
+CLANG_SUPPORTS_V4=$(if $(findstring v4,$(shell $(CLANG) --target=bpf -mcpu=? 2>&1)),true,)
+ifeq ($(CLANG_SUPPORTS_V4),true)
+	CFLAGS += -DENABLE_ATOMICS_TESTS
+endif
+
 CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
 BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN) 			\
 	     -I$(INCLUDE_DIR) -I$(CURDIR) -I$(APIDIR)			\
@@ -250,7 +256,9 @@ define CLANG_BPF_BUILD_RULE
 	$(call msg,CLNG-LLC,$(TRUNNER_BINARY),$2)
 	$(Q)($(CLANG) $3 -O2 -target bpf -emit-llvm			\
 		-c $1 -o - || echo "BPF obj compilation failed") | 	\
-	$(LLC) -mattr=dwarfris -march=bpf -mcpu=v3 $4 -filetype=obj -o $2
+	$(LLC) -mattr=dwarfris -march=bpf				\
+		-mcpu=$(if $(CLANG_SUPPORTS_V4),v4,v3)			\
+		$4 -filetype=obj -o $2
 endef
 # Similar to CLANG_BPF_BUILD_RULE, but with disabled alu32
 define CLANG_NOALU32_BPF_BUILD_RULE
@@ -391,7 +399,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c trace_helpers.c	\
 TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read				\
 		       $(wildcard progs/btf_dump_test_case_*.c)
 TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
-TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS)
+TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS) $(if $(CLANG_SUPPORTS_V4),-DENABLE_ATOMICS_TESTS,)
 TRUNNER_BPF_LDFLAGS := -mattr=+alu32
 $(eval $(call DEFINE_TEST_RUNNER,test_progs))
 
diff --git a/tools/testing/selftests/bpf/prog_tests/atomics_test.c b/tools/testing/selftests/bpf/prog_tests/atomics_test.c
new file mode 100644
index 000000000000..8ecc0392fdf9
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/atomics_test.c
@@ -0,0 +1,329 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <test_progs.h>
+
+#ifdef ENABLE_ATOMICS_TESTS
+
+#include "atomics_test.skel.h"
+
+static void test_add(void)
+{
+	struct atomics_test *atomics_skel = NULL;
+	int err, prog_fd;
+	__u32 duration = 0, retval;
+
+	atomics_skel = atomics_test__open_and_load();
+	if (CHECK(!atomics_skel, "atomics_skel_load", "atomics skeleton failed\n"))
+		goto cleanup;
+
+	err = atomics_test__attach(atomics_skel);
+	if (CHECK(err, "atomics_attach", "atomics attach failed: %d\n", err))
+		goto cleanup;
+
+	prog_fd = bpf_program__fd(atomics_skel->progs.add);
+	err = bpf_prog_test_run(prog_fd, 1, NULL, 0,
+				NULL, NULL, &retval, &duration);
+	if (CHECK(err || retval, "test_run add",
+		  "err %d errno %d retval %d duration %d\n",
+		  err, errno, retval, duration))
+		goto cleanup;
+
+	CHECK(atomics_skel->data->add64_value != 3, "add64_value",
+	      "64bit atomic add value was not incremented (got %lld want 2)\n",
+	      atomics_skel->data->add64_value);
+	CHECK(atomics_skel->bss->add64_result != 1, "add64_result",
+	      "64bit atomic add bad return value (got %lld want 1)\n",
+	      atomics_skel->bss->add64_result);
+
+	CHECK(atomics_skel->data->add32_value != 3, "add32_value",
+	      "32bit atomic add value was not incremented (got %d want 2)\n",
+	      atomics_skel->data->add32_value);
+	CHECK(atomics_skel->bss->add32_result != 1, "add32_result",
+	      "32bit atomic add bad return value (got %d want 1)\n",
+	      atomics_skel->bss->add32_result);
+
+	CHECK(atomics_skel->bss->add_stack_value_copy != 3, "add_stack_value",
+	      "stack atomic add value was not incremented (got %lld want 2)\n",
+	      atomics_skel->bss->add_stack_value_copy);
+	CHECK(atomics_skel->bss->add_stack_result != 1, "add_stack_result",
+	      "stack atomic add bad return value (got %lld want 1)\n",
+	      atomics_skel->bss->add_stack_result);
+
+cleanup:
+	atomics_test__destroy(atomics_skel);
+}
+
+static void test_sub(void)
+{
+	struct atomics_test *atomics_skel = NULL;
+	int err, prog_fd;
+	__u32 duration = 0, retval;
+
+	atomics_skel = atomics_test__open_and_load();
+	if (CHECK(!atomics_skel, "atomics_skel_load", "atomics skeleton failed\n"))
+		goto cleanup;
+
+	err = atomics_test__attach(atomics_skel);
+	if (CHECK(err, "atomics_attach", "atomics attach failed: %d\n", err))
+		goto cleanup;
+
+	prog_fd = bpf_program__fd(atomics_skel->progs.sub);
+	err = bpf_prog_test_run(prog_fd, 1, NULL, 0,
+				NULL, NULL, &retval, &duration);
+	if (CHECK(err || retval, "test_run sub",
+		  "err %d errno %d retval %d duration %d\n",
+		  err, errno, retval, duration))
+		goto cleanup;
+
+	CHECK(atomics_skel->data->sub64_value != -1, "sub64_value",
+	      "64bit atomic sub value was not decremented (got %lld want -1)\n",
+	      atomics_skel->data->sub64_value);
+	CHECK(atomics_skel->bss->sub64_result != 1, "sub64_result",
+	      "64bit atomic sub bad return value (got %lld want 1)\n",
+	      atomics_skel->bss->sub64_result);
+
+	CHECK(atomics_skel->data->sub32_value != -1, "sub32_value",
+	      "32bit atomic sub value was not decremented (got %d want -1)\n",
+	      atomics_skel->data->sub32_value);
+	CHECK(atomics_skel->bss->sub32_result != 1, "sub32_result",
+	      "32bit atomic sub bad return value (got %d want 1)\n",
+	      atomics_skel->bss->sub32_result);
+
+	CHECK(atomics_skel->bss->sub_stack_value_copy != -1, "sub_stack_value",
+	      "stack atomic sub value was not decremented (got %lld want -1)\n",
+	      atomics_skel->bss->sub_stack_value_copy);
+	CHECK(atomics_skel->bss->sub_stack_result != 1, "sub_stack_result",
+	      "stack atomic sub bad return value (got %lld want 1)\n",
+	      atomics_skel->bss->sub_stack_result);
+
+cleanup:
+	atomics_test__destroy(atomics_skel);
+}
+
+static void test_and(void)
+{
+	struct atomics_test *atomics_skel = NULL;
+	int err, prog_fd;
+	__u32 duration = 0, retval;
+
+	atomics_skel = atomics_test__open_and_load();
+	if (CHECK(!atomics_skel, "atomics_skel_load", "atomics skeleton failed\n"))
+		goto cleanup;
+
+	err = atomics_test__attach(atomics_skel);
+	if (CHECK(err, "atomics_attach", "atomics attach failed: %d\n", err))
+		goto cleanup;
+
+	prog_fd = bpf_program__fd(atomics_skel->progs.and);
+	err = bpf_prog_test_run(prog_fd, 1, NULL, 0,
+				NULL, NULL, &retval, &duration);
+	if (CHECK(err || retval, "test_run and",
+		  "err %d errno %d retval %d duration %d\n",
+		  err, errno, retval, duration))
+		goto cleanup;
+
+	CHECK(atomics_skel->data->and64_value != 0x010ull << 32, "and64_value",
+	      "64bit atomic and, bad value (got 0x%llx want 0x%llx)\n",
+	      atomics_skel->data->and64_value, 0x010ull << 32);
+	CHECK(atomics_skel->bss->and64_result != 0x110ull << 32, "and64_result",
+	      "64bit atomic and, bad result (got 0x%llx want 0x%llx)\n",
+	      atomics_skel->bss->and64_result, 0x110ull << 32);
+
+	CHECK(atomics_skel->data->and32_value != 0x010, "and32_value",
+	      "32bit atomic and, bad value (got 0x%x want 0x%x)\n",
+	      atomics_skel->data->and32_value, 0x010);
+	CHECK(atomics_skel->bss->and32_result != 0x110, "and32_result",
+	      "32bit atomic and, bad result (got 0x%x want 0x%x)\n",
+	      atomics_skel->bss->and32_result, 0x110);
+
+cleanup:
+	atomics_test__destroy(atomics_skel);
+}
+
+static void test_or(void)
+{
+	struct atomics_test *atomics_skel = NULL;
+	int err, prog_fd;
+	__u32 duration = 0, retval;
+
+	atomics_skel = atomics_test__open_and_load();
+	if (CHECK(!atomics_skel, "atomics_skel_load", "atomics skeleton failed\n"))
+		goto cleanup;
+
+	err = atomics_test__attach(atomics_skel);
+	if (CHECK(err, "atomics_attach", "atomics attach failed: %d\n", err))
+		goto cleanup;
+
+	prog_fd = bpf_program__fd(atomics_skel->progs.or);
+	err = bpf_prog_test_run(prog_fd, 1, NULL, 0,
+				NULL, NULL, &retval, &duration);
+	if (CHECK(err || retval, "test_run or",
+		  "err %d errno %d retval %d duration %d\n",
+		  err, errno, retval, duration))
+		goto cleanup;
+
+	CHECK(atomics_skel->data->or64_value != 0x111ull << 32, "or64_value",
+	      "64bit atomic or, bad value (got 0x%llx want 0x%llx)\n",
+	      atomics_skel->data->or64_value, 0x111ull << 32);
+	CHECK(atomics_skel->bss->or64_result != 0x110ull << 32, "or64_result",
+	      "64bit atomic or, bad result (got 0x%llx want 0x%llx)\n",
+	      atomics_skel->bss->or64_result, 0x110ull << 32);
+
+	CHECK(atomics_skel->data->or32_value != 0x111, "or32_value",
+	      "32bit atomic or, bad value (got 0x%x want 0x%x)\n",
+	      atomics_skel->data->or32_value, 0x111);
+	CHECK(atomics_skel->bss->or32_result != 0x110, "or32_result",
+	      "32bit atomic or, bad result (got 0x%x want 0x%x)\n",
+	      atomics_skel->bss->or32_result, 0x110);
+
+cleanup:
+	atomics_test__destroy(atomics_skel);
+}
+
+static void test_xor(void)
+{
+	struct atomics_test *atomics_skel = NULL;
+	int err, prog_fd;
+	__u32 duration = 0, retval;
+
+	atomics_skel = atomics_test__open_and_load();
+	if (CHECK(!atomics_skel, "atomics_skel_load", "atomics skeleton failed\n"))
+		goto cleanup;
+
+	err = atomics_test__attach(atomics_skel);
+	if (CHECK(err, "atomics_attach", "atomics attach failed: %d\n", err))
+		goto cleanup;
+
+	prog_fd = bpf_program__fd(atomics_skel->progs.xor);
+	err = bpf_prog_test_run(prog_fd, 1, NULL, 0,
+				NULL, NULL, &retval, &duration);
+	if (CHECK(err || retval, "test_run xor",
+		  "err %d errno %d retval %d duration %d\n",
+		  err, errno, retval, duration))
+		goto cleanup;
+
+	CHECK(atomics_skel->data->xor64_value != 0x101ull << 32, "xor64_value",
+	      "64bit atomic xor, bad value (got 0x%llx want 0x%llx)\n",
+	      atomics_skel->data->xor64_value, 0x101ull << 32);
+	CHECK(atomics_skel->bss->xor64_result != 0x110ull << 32, "xor64_result",
+	      "64bit atomic xor, bad result (got 0x%llx want 0x%llx)\n",
+	      atomics_skel->bss->xor64_result, 0x110ull << 32);
+
+	CHECK(atomics_skel->data->xor32_value != 0x101, "xor32_value",
+	      "32bit atomic xor, bad value (got 0x%x want 0x%x)\n",
+	      atomics_skel->data->xor32_value, 0x101);
+	CHECK(atomics_skel->bss->xor32_result != 0x110, "xor32_result",
+	      "32bit atomic xor, bad result (got 0x%x want 0x%x)\n",
+	      atomics_skel->bss->xor32_result, 0x110);
+
+cleanup:
+	atomics_test__destroy(atomics_skel);
+}
+
+static void test_cmpxchg(void)
+{
+	struct atomics_test *atomics_skel = NULL;
+	int err, prog_fd;
+	__u32 duration = 0, retval;
+
+	atomics_skel = atomics_test__open_and_load();
+	if (CHECK(!atomics_skel, "atomics_skel_load", "atomics skeleton failed\n"))
+		goto cleanup;
+
+	err = atomics_test__attach(atomics_skel);
+	if (CHECK(err, "atomics_attach", "atomics attach failed: %d\n", err))
+		goto cleanup;
+
+	prog_fd = bpf_program__fd(atomics_skel->progs.add);
+	err = bpf_prog_test_run(prog_fd, 1, NULL, 0,
+				NULL, NULL, &retval, &duration);
+	if (CHECK(err || retval, "test_run add",
+		  "err %d errno %d retval %d duration %d\n",
+		  err, errno, retval, duration))
+		goto cleanup;
+
+	CHECK(atomics_skel->data->cmpxchg64_value != 2, "cmpxchg64_value",
+	      "64bit cmpxchg left unexpected value (got %llx want 2)\n",
+	      atomics_skel->data->cmpxchg64_value);
+	CHECK(atomics_skel->bss->cmpxchg64_result_fail != 1, "cmpxchg_result_fail",
+	      "64bit cmpxchg returned bad result (got %llx want 1)\n",
+	      atomics_skel->bss->cmpxchg64_result_fail);
+	CHECK(atomics_skel->bss->cmpxchg64_result_succeed != 1, "cmpxchg_result_succeed",
+	      "64bit cmpxchg returned bad result (got %llx want 1)\n",
+	      atomics_skel->bss->cmpxchg64_result_succeed);
+
+	CHECK(atomics_skel->data->cmpxchg32_value != 2, "cmpxchg32_value",
+	      "32bit cmpxchg left unexpected value (got %d want 2)\n",
+	      atomics_skel->data->cmpxchg32_value);
+	CHECK(atomics_skel->bss->cmpxchg32_result_fail != 1, "cmpxchg_result_fail",
+	      "32bit cmpxchg returned bad result (got %d want 1)\n",
+	      atomics_skel->bss->cmpxchg32_result_fail);
+	CHECK(atomics_skel->bss->cmpxchg32_result_succeed != 1, "cmpxchg_result_succeed",
+	      "32bit cmpxchg returned bad result (got %d want 1)\n",
+	      atomics_skel->bss->cmpxchg32_result_succeed);
+
+cleanup:
+	atomics_test__destroy(atomics_skel);
+}
+
+static void test_xchg(void)
+{
+	struct atomics_test *atomics_skel = NULL;
+	int err, prog_fd;
+	__u32 duration = 0, retval;
+
+	atomics_skel = atomics_test__open_and_load();
+	if (CHECK(!atomics_skel, "atomics_skel_load", "atomics skeleton failed\n"))
+		goto cleanup;
+
+	err = atomics_test__attach(atomics_skel);
+	if (CHECK(err, "atomics_attach", "atomics attach failed: %d\n", err))
+		goto cleanup;
+
+	prog_fd = bpf_program__fd(atomics_skel->progs.add);
+	err = bpf_prog_test_run(prog_fd, 1, NULL, 0,
+				NULL, NULL, &retval, &duration);
+	if (CHECK(err || retval, "test_run add",
+		  "err %d errno %d retval %d duration %d\n",
+		  err, errno, retval, duration))
+		goto cleanup;
+
+	CHECK(atomics_skel->data->xchg64_value != 2, "xchg64_value",
+	      "64bit xchg left unexpected value (got %lld want 2)\n",
+	      atomics_skel->data->xchg64_value);
+	CHECK(atomics_skel->bss->xchg64_result != 1, "xchg_result",
+	      "64bit xchg returned bad result (got %lld want 1)\n",
+	      atomics_skel->bss->xchg64_result);
+
+	CHECK(atomics_skel->data->xchg32_value != 2, "xchg32_value",
+	      "32bit xchg left unexpected value (got %d want 2)\n",
+	      atomics_skel->data->xchg32_value);
+	CHECK(atomics_skel->bss->xchg32_result != 1, "xchg_result",
+	      "32bit xchg returned bad result (got %d want 1)\n",
+	      atomics_skel->bss->xchg32_result);
+
+cleanup:
+	atomics_test__destroy(atomics_skel);
+}
+
+void test_atomics_test(void)
+{
+	test_add();
+	test_sub();
+	test_and();
+	test_or();
+	test_xor();
+	test_cmpxchg();
+	test_xchg();
+}
+
+#else /* ENABLE_ATOMICS_TESTS */
+
+void test_atomics_test(void)
+{
+	printf("%s:SKIP:no ENABLE_ATOMICS_TEST (missing Clang BPF atomics support)",
+	       __func__);
+	test__skip();
+}
+
+#endif /* ENABLE_ATOMICS_TESTS */
diff --git a/tools/testing/selftests/bpf/progs/atomics_test.c b/tools/testing/selftests/bpf/progs/atomics_test.c
new file mode 100644
index 000000000000..3139b00937e5
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/atomics_test.c
@@ -0,0 +1,124 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+#ifdef ENABLE_ATOMICS_TESTS
+
+__u64 add64_value = 1;
+__u64 add64_result = 0;
+__u32 add32_value = 1;
+__u32 add32_result = 0;
+__u64 add_stack_value_copy = 0;
+__u64 add_stack_result = 0;
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(add, int a)
+{
+	__u64 add_stack_value = 1;
+
+	add64_result = __sync_fetch_and_add(&add64_value, 2);
+	add32_result = __sync_fetch_and_add(&add32_value, 2);
+	add_stack_result = __sync_fetch_and_add(&add_stack_value, 2);
+	add_stack_value_copy = add_stack_value;
+
+	return 0;
+}
+
+__s64 sub64_value = 1;
+__s64 sub64_result = 0;
+__s32 sub32_value = 1;
+__s32 sub32_result = 0;
+__s64 sub_stack_value_copy = 0;
+__s64 sub_stack_result = 0;
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(sub, int a)
+{
+	__u64 sub_stack_value = 1;
+
+	sub64_result = __sync_fetch_and_sub(&sub64_value, 2);
+	sub32_result = __sync_fetch_and_sub(&sub32_value, 2);
+	sub_stack_result = __sync_fetch_and_sub(&sub_stack_value, 2);
+	sub_stack_value_copy = sub_stack_value;
+
+	return 0;
+}
+
+__u64 and64_value = (0x110ull << 32);
+__u64 and64_result = 0;
+__u32 and32_value = 0x110;
+__u32 and32_result = 0;
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(and, int a)
+{
+
+	and64_result = __sync_fetch_and_and(&and64_value, 0x011ull << 32);
+	and32_result = __sync_fetch_and_and(&and32_value, 0x011);
+
+	return 0;
+}
+
+__u64 or64_value = (0x110ull << 32);
+__u64 or64_result = 0;
+__u32 or32_value = 0x110;
+__u32 or32_result = 0;
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(or, int a)
+{
+	or64_result = __sync_fetch_and_or(&or64_value, 0x011ull << 32);
+	or32_result = __sync_fetch_and_or(&or32_value, 0x011);
+
+	return 0;
+}
+
+__u64 xor64_value = (0x110ull << 32);
+__u64 xor64_result = 0;
+__u32 xor32_value = 0x110;
+__u32 xor32_result = 0;
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(xor, int a)
+{
+	xor64_result = __sync_fetch_and_xor(&xor64_value, 0x011ull << 32);
+	xor32_result = __sync_fetch_and_xor(&xor32_value, 0x011);
+
+	return 0;
+}
+
+__u64 cmpxchg64_value = 1;
+__u64 cmpxchg64_result_fail = 0;
+__u64 cmpxchg64_result_succeed = 0;
+__u32 cmpxchg32_value = 1;
+__u32 cmpxchg32_result_fail = 0;
+__u32 cmpxchg32_result_succeed = 0;
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(cmpxchg, int a)
+{
+	cmpxchg64_result_fail = __sync_val_compare_and_swap(
+		&cmpxchg64_value, 0, 3);
+	cmpxchg64_result_succeed = __sync_val_compare_and_swap(
+		&cmpxchg64_value, 1, 2);
+
+	cmpxchg32_result_fail = __sync_val_compare_and_swap(
+		&cmpxchg32_value, 0, 3);
+	cmpxchg32_result_succeed = __sync_val_compare_and_swap(
+		&cmpxchg32_value, 1, 2);
+
+	return 0;
+}
+
+__u64 xchg64_value = 1;
+__u64 xchg64_result = 0;
+__u32 xchg32_value = 1;
+__u32 xchg32_result = 0;
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(xchg, int a)
+{
+	__u64 val64 = 2;
+	__u32 val32 = 2;
+
+	__atomic_exchange(&xchg64_value, &val64, &xchg64_result, __ATOMIC_RELAXED);
+	__atomic_exchange(&xchg32_value, &val32, &xchg32_result, __ATOMIC_RELAXED);
+
+	return 0;
+}
+
+#endif /* ENABLE_ATOMICS_TESTS */
diff --git a/tools/testing/selftests/bpf/verifier/atomic_and.c b/tools/testing/selftests/bpf/verifier/atomic_and.c
new file mode 100644
index 000000000000..7eea6d9dfd7d
--- /dev/null
+++ b/tools/testing/selftests/bpf/verifier/atomic_and.c
@@ -0,0 +1,77 @@
+{
+	"BPF_ATOMIC_AND without fetch",
+	.insns = {
+		/* val = 0x110; */
+		BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0x110),
+		/* atomic_and(&val, 0x011); */
+		BPF_MOV64_IMM(BPF_REG_1, 0x011),
+		BPF_ATOMIC_AND(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
+		/* if (val != 0x010) exit(2); */
+		BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_10, -8),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0x010, 2),
+		BPF_MOV64_IMM(BPF_REG_0, 2),
+		BPF_EXIT_INSN(),
+		/* r1 should not be clobbered, no BPF_FETCH flag */
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0x011, 1),
+		BPF_MOV64_IMM(BPF_REG_0, 1),
+		BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
+{
+	"BPF_ATOMIC_AND with fetch",
+	.insns = {
+		BPF_MOV64_IMM(BPF_REG_0, 123),
+		/* val = 0x110; */
+		BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0x110),
+		/* old = atomic_fetch_and(&val, 0x011); */
+		BPF_MOV64_IMM(BPF_REG_1, 0x011),
+		BPF_ATOMIC_FETCH_AND(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
+		/* if (old != 0x110) exit(3); */
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0x110, 2),
+		BPF_MOV64_IMM(BPF_REG_0, 3),
+		BPF_EXIT_INSN(),
+		/* if (val != 0x010) exit(2); */
+		BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_10, -8),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0x010, 2),
+		BPF_MOV64_IMM(BPF_REG_1, 2),
+		BPF_EXIT_INSN(),
+		/* Check R0 wasn't clobbered (for fear of x86 JIT bug) */
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 123, 2),
+		BPF_MOV64_IMM(BPF_REG_0, 1),
+		BPF_EXIT_INSN(),
+		/* exit(0); */
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
+{
+	"BPF_ATOMIC_AND with fetch 32bit",
+	.insns = {
+		/* r0 = (s64) -1 */
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_ALU64_IMM(BPF_SUB, BPF_REG_0, 1),
+		/* val = 0x110; */
+		BPF_ST_MEM(BPF_W, BPF_REG_10, -4, 0x110),
+		/* old = atomic_fetch_and(&val, 0x011); */
+		BPF_MOV32_IMM(BPF_REG_1, 0x011),
+		BPF_ATOMIC_FETCH_AND(BPF_W, BPF_REG_10, BPF_REG_1, -4),
+		/* if (old != 0x110) exit(3); */
+		BPF_JMP32_IMM(BPF_JEQ, BPF_REG_1, 0x110, 2),
+		BPF_MOV32_IMM(BPF_REG_0, 3),
+		BPF_EXIT_INSN(),
+		/* if (val != 0x010) exit(2); */
+		BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_10, -4),
+		BPF_JMP32_IMM(BPF_JEQ, BPF_REG_1, 0x010, 2),
+		BPF_MOV32_IMM(BPF_REG_1, 2),
+		BPF_EXIT_INSN(),
+		/* Check R0 wasn't clobbered (for fear of x86 JIT bug)
+		 * It should be -1 so add 1 to get exit code.
+		 */
+		BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 1),
+		BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
diff --git a/tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c b/tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c
new file mode 100644
index 000000000000..eb43a06428fa
--- /dev/null
+++ b/tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c
@@ -0,0 +1,96 @@
+{
+	"atomic compare-and-exchange smoketest - 64bit",
+	.insns = {
+	/* val = 3; */
+	BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 3),
+	/* old = atomic_cmpxchg(&val, 2, 4); */
+	BPF_MOV64_IMM(BPF_REG_1, 4),
+	BPF_MOV64_IMM(BPF_REG_0, 2),
+	BPF_ATOMIC_CMPXCHG(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
+	/* if (old != 3) exit(2); */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 3, 2),
+	BPF_MOV64_IMM(BPF_REG_0, 2),
+	BPF_EXIT_INSN(),
+	/* if (val != 3) exit(3); */
+	BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_10, -8),
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 3, 2),
+	BPF_MOV64_IMM(BPF_REG_0, 3),
+	BPF_EXIT_INSN(),
+	/* old = atomic_cmpxchg(&val, 3, 4); */
+	BPF_MOV64_IMM(BPF_REG_1, 4),
+	BPF_MOV64_IMM(BPF_REG_0, 3),
+	BPF_ATOMIC_CMPXCHG(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
+	/* if (old != 3) exit(4); */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 3, 2),
+	BPF_MOV64_IMM(BPF_REG_0, 4),
+	BPF_EXIT_INSN(),
+	/* if (val != 4) exit(5); */
+	BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_10, -8),
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 4, 2),
+	BPF_MOV64_IMM(BPF_REG_0, 5),
+	BPF_EXIT_INSN(),
+	/* exit(0); */
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
+{
+	"atomic compare-and-exchange smoketest - 32bit",
+	.insns = {
+	/* val = 3; */
+	BPF_ST_MEM(BPF_W, BPF_REG_10, -4, 3),
+	/* old = atomic_cmpxchg(&val, 2, 4); */
+	BPF_MOV32_IMM(BPF_REG_1, 4),
+	BPF_MOV32_IMM(BPF_REG_0, 2),
+	BPF_ATOMIC_CMPXCHG(BPF_W, BPF_REG_10, BPF_REG_1, -4),
+	/* if (old != 3) exit(2); */
+	BPF_JMP32_IMM(BPF_JEQ, BPF_REG_0, 3, 2),
+	BPF_MOV32_IMM(BPF_REG_0, 2),
+	BPF_EXIT_INSN(),
+	/* if (val != 3) exit(3); */
+	BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_10, -4),
+	BPF_JMP32_IMM(BPF_JEQ, BPF_REG_0, 3, 2),
+	BPF_MOV32_IMM(BPF_REG_0, 3),
+	BPF_EXIT_INSN(),
+	/* old = atomic_cmpxchg(&val, 3, 4); */
+	BPF_MOV32_IMM(BPF_REG_1, 4),
+	BPF_MOV32_IMM(BPF_REG_0, 3),
+	BPF_ATOMIC_CMPXCHG(BPF_W, BPF_REG_10, BPF_REG_1, -4),
+	/* if (old != 3) exit(4); */
+	BPF_JMP32_IMM(BPF_JEQ, BPF_REG_0, 3, 2),
+	BPF_MOV32_IMM(BPF_REG_0, 4),
+	BPF_EXIT_INSN(),
+	/* if (val != 4) exit(5); */
+	BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_10, -4),
+	BPF_JMP32_IMM(BPF_JEQ, BPF_REG_0, 4, 2),
+	BPF_MOV32_IMM(BPF_REG_0, 5),
+	BPF_EXIT_INSN(),
+	/* exit(0); */
+	BPF_MOV32_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
+{
+	"Can't use cmpxchg on uninit src reg",
+	.insns = {
+	BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 3),
+	BPF_MOV64_IMM(BPF_REG_0, 3),
+	BPF_ATOMIC_CMPXCHG(BPF_DW, BPF_REG_10, BPF_REG_2, -8),
+	BPF_EXIT_INSN(),
+	},
+	.result = REJECT,
+	.errstr = "!read_ok",
+},
+{
+	"Can't use cmpxchg on uninit memory",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_0, 3),
+	BPF_MOV64_IMM(BPF_REG_2, 4),
+	BPF_ATOMIC_CMPXCHG(BPF_DW, BPF_REG_10, BPF_REG_2, -8),
+	BPF_EXIT_INSN(),
+	},
+	.result = REJECT,
+	.errstr = "invalid read from stack",
+},
diff --git a/tools/testing/selftests/bpf/verifier/atomic_fetch_add.c b/tools/testing/selftests/bpf/verifier/atomic_fetch_add.c
new file mode 100644
index 000000000000..c3236510cb64
--- /dev/null
+++ b/tools/testing/selftests/bpf/verifier/atomic_fetch_add.c
@@ -0,0 +1,106 @@
+{
+	"BPF_ATOMIC_FETCH_ADD smoketest - 64bit",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	/* Write 3 to stack */
+	BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 3),
+	/* Put a 1 in R1, add it to the 3 on the stack, and load the value back into R1 */
+	BPF_MOV64_IMM(BPF_REG_1, 1),
+	BPF_ATOMIC_FETCH_ADD(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
+	/* Check the value we loaded back was 3 */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 3, 2),
+	BPF_MOV64_IMM(BPF_REG_0, 1),
+	BPF_EXIT_INSN(),
+	/* Load value from stack */
+	BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_10, -8),
+	/* Check value loaded from stack was 4 */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 4, 1),
+	BPF_MOV64_IMM(BPF_REG_0, 2),
+	BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
+{
+	"BPF_ATOMIC_FETCH_ADD smoketest - 32bit",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	/* Write 3 to stack */
+	BPF_ST_MEM(BPF_W, BPF_REG_10, -4, 3),
+	/* Put a 1 in R1, add it to the 3 on the stack, and load the value back into R1 */
+	BPF_MOV32_IMM(BPF_REG_1, 1),
+	BPF_ATOMIC_FETCH_ADD(BPF_W, BPF_REG_10, BPF_REG_1, -4),
+	/* Check the value we loaded back was 3 */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 3, 2),
+	BPF_MOV64_IMM(BPF_REG_0, 1),
+	BPF_EXIT_INSN(),
+	/* Load value from stack */
+	BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_10, -4),
+	/* Check value loaded from stack was 4 */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 4, 1),
+	BPF_MOV64_IMM(BPF_REG_0, 2),
+	BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
+{
+	"Can't use ATM_FETCH_ADD on frame pointer",
+	.insns = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 3),
+		BPF_ATOMIC_FETCH_ADD(BPF_DW, BPF_REG_10, BPF_REG_10, -8),
+		BPF_EXIT_INSN(),
+	},
+	.result = REJECT,
+	.errstr_unpriv = "R10 leaks addr into mem",
+	.errstr = "frame pointer is read only",
+},
+{
+	"Can't use ATM_FETCH_ADD on uninit src reg",
+	.insns = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 3),
+		BPF_ATOMIC_FETCH_ADD(BPF_DW, BPF_REG_10, BPF_REG_2, -8),
+		BPF_EXIT_INSN(),
+	},
+	.result = REJECT,
+	/* It happens that the address leak check is first, but it would also be
+	 * complain about the fact that we're trying to modify R10.
+	 */
+	.errstr = "!read_ok",
+},
+{
+	"Can't use ATM_FETCH_ADD on uninit dst reg",
+	.insns = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_ATOMIC_FETCH_ADD(BPF_DW, BPF_REG_2, BPF_REG_0, -8),
+		BPF_EXIT_INSN(),
+	},
+	.result = REJECT,
+	/* It happens that the address leak check is first, but it would also be
+	 * complain about the fact that we're trying to modify R10.
+	 */
+	.errstr = "!read_ok",
+},
+{
+	"Can't use ATM_FETCH_ADD on kernel memory",
+	.insns = {
+		/* This is an fentry prog, context is array of the args of the
+		 * kernel function being called. Load first arg into R2.
+		 */
+		BPF_LDX_MEM(BPF_DW, BPF_REG_2, BPF_REG_1, 0),
+		/* First arg of bpf_fentry_test7 is a pointer to a struct.
+		 * Attempt to modify that struct. Verifier shouldn't let us
+		 * because it's kernel memory.
+		 */
+		BPF_MOV64_IMM(BPF_REG_3, 1),
+		BPF_ATOMIC_FETCH_ADD(BPF_DW, BPF_REG_2, BPF_REG_3, 0),
+		/* Done */
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_TRACING,
+	.expected_attach_type = BPF_TRACE_FENTRY,
+	.kfunc = "bpf_fentry_test7",
+	.result = REJECT,
+	.errstr = "only read is supported",
+},
diff --git a/tools/testing/selftests/bpf/verifier/atomic_or.c b/tools/testing/selftests/bpf/verifier/atomic_or.c
new file mode 100644
index 000000000000..1b22fb2881f0
--- /dev/null
+++ b/tools/testing/selftests/bpf/verifier/atomic_or.c
@@ -0,0 +1,77 @@
+{
+	"BPF_ATOMIC_OR without fetch",
+	.insns = {
+		/* val = 0x110; */
+		BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0x110),
+		/* atomic_or(&val, 0x011); */
+		BPF_MOV64_IMM(BPF_REG_1, 0x011),
+		BPF_ATOMIC_OR(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
+		/* if (val != 0x111) exit(2); */
+		BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_10, -8),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0x111, 2),
+		BPF_MOV64_IMM(BPF_REG_0, 2),
+		BPF_EXIT_INSN(),
+		/* r1 should not be clobbered, no BPF_FETCH flag */
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0x011, 1),
+		BPF_MOV64_IMM(BPF_REG_0, 1),
+		BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
+{
+	"BPF_ATOMIC_OR with fetch",
+	.insns = {
+		BPF_MOV64_IMM(BPF_REG_0, 123),
+		/* val = 0x110; */
+		BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0x110),
+		/* old = atomic_fetch_or(&val, 0x011); */
+		BPF_MOV64_IMM(BPF_REG_1, 0x011),
+		BPF_ATOMIC_FETCH_OR(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
+		/* if (old != 0x110) exit(3); */
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0x110, 2),
+		BPF_MOV64_IMM(BPF_REG_0, 3),
+		BPF_EXIT_INSN(),
+		/* if (val != 0x111) exit(2); */
+		BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_10, -8),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0x111, 2),
+		BPF_MOV64_IMM(BPF_REG_1, 2),
+		BPF_EXIT_INSN(),
+		/* Check R0 wasn't clobbered (for fear of x86 JIT bug) */
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 123, 2),
+		BPF_MOV64_IMM(BPF_REG_0, 1),
+		BPF_EXIT_INSN(),
+		/* exit(0); */
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
+{
+	"BPF_ATOMIC_OR with fetch 32bit",
+	.insns = {
+		/* r0 = (s64) -1 */
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_ALU64_IMM(BPF_SUB, BPF_REG_0, 1),
+		/* val = 0x110; */
+		BPF_ST_MEM(BPF_W, BPF_REG_10, -4, 0x110),
+		/* old = atomic_fetch_or(&val, 0x011); */
+		BPF_MOV32_IMM(BPF_REG_1, 0x011),
+		BPF_ATOMIC_FETCH_OR(BPF_W, BPF_REG_10, BPF_REG_1, -4),
+		/* if (old != 0x110) exit(3); */
+		BPF_JMP32_IMM(BPF_JEQ, BPF_REG_1, 0x110, 2),
+		BPF_MOV32_IMM(BPF_REG_0, 3),
+		BPF_EXIT_INSN(),
+		/* if (val != 0x111) exit(2); */
+		BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_10, -4),
+		BPF_JMP32_IMM(BPF_JEQ, BPF_REG_1, 0x111, 2),
+		BPF_MOV32_IMM(BPF_REG_1, 2),
+		BPF_EXIT_INSN(),
+		/* Check R0 wasn't clobbered (for fear of x86 JIT bug)
+		 * It should be -1 so add 1 to get exit code.
+		 */
+		BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 1),
+		BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
diff --git a/tools/testing/selftests/bpf/verifier/atomic_sub.c b/tools/testing/selftests/bpf/verifier/atomic_sub.c
new file mode 100644
index 000000000000..8a198f8bc194
--- /dev/null
+++ b/tools/testing/selftests/bpf/verifier/atomic_sub.c
@@ -0,0 +1,44 @@
+{
+	"BPF_ATOMIC_SUB without fetch",
+	.insns = {
+		/* val = 100; */
+		BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 100),
+		/* atomic_sub(&val, 4); */
+		BPF_MOV64_IMM(BPF_REG_1, 4),
+		BPF_ATOMIC_SUB(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
+		/* if (val != 96) exit(2); */
+		BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_10, -8),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 96, 2),
+		BPF_MOV64_IMM(BPF_REG_0, 2),
+		BPF_EXIT_INSN(),
+		/* r1 should not be clobbered, no BPF_FETCH flag */
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 4, 1),
+		BPF_MOV64_IMM(BPF_REG_0, 1),
+		BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
+{
+	"BPF_ATOMIC_SUB with fetch",
+	.insns = {
+		/* val = 100; */
+		BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 100),
+		/* old = atomic_fetch_sub(&val, 4); */
+		BPF_MOV64_IMM(BPF_REG_1, 4),
+		BPF_ATOMIC_FETCH_SUB(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
+		/* if (old != 100) exit(3); */
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 100, 2),
+		BPF_MOV64_IMM(BPF_REG_0, 3),
+		BPF_EXIT_INSN(),
+		/* if (val != 96) exit(2); */
+		BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_10, -8),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 96, 2),
+		BPF_MOV64_IMM(BPF_REG_0, 2),
+		BPF_EXIT_INSN(),
+		/* exit(0); */
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
diff --git a/tools/testing/selftests/bpf/verifier/atomic_xchg.c b/tools/testing/selftests/bpf/verifier/atomic_xchg.c
new file mode 100644
index 000000000000..6ab7b2bdc6b7
--- /dev/null
+++ b/tools/testing/selftests/bpf/verifier/atomic_xchg.c
@@ -0,0 +1,46 @@
+{
+	"atomic exchange smoketest - 64bit",
+	.insns = {
+	/* val = 3; */
+	BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 3),
+	/* old = atomic_xchg(&val, 4); */
+	BPF_MOV64_IMM(BPF_REG_1, 4),
+	BPF_ATOMIC_XCHG(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
+	/* if (old != 3) exit(1); */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 3, 2),
+	BPF_MOV64_IMM(BPF_REG_0, 1),
+	BPF_EXIT_INSN(),
+	/* if (val != 4) exit(2); */
+	BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_10, -8),
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 4, 2),
+	BPF_MOV64_IMM(BPF_REG_0, 2),
+	BPF_EXIT_INSN(),
+	/* exit(0); */
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
+{
+	"atomic exchange smoketest - 32bit",
+	.insns = {
+	/* val = 3; */
+	BPF_ST_MEM(BPF_W, BPF_REG_10, -4, 3),
+	/* old = atomic_xchg(&val, 4); */
+	BPF_MOV32_IMM(BPF_REG_1, 4),
+	BPF_ATOMIC_XCHG(BPF_W, BPF_REG_10, BPF_REG_1, -4),
+	/* if (old != 3) exit(1); */
+	BPF_JMP32_IMM(BPF_JEQ, BPF_REG_1, 3, 2),
+	BPF_MOV32_IMM(BPF_REG_0, 1),
+	BPF_EXIT_INSN(),
+	/* if (val != 4) exit(2); */
+	BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_10, -4),
+	BPF_JMP32_IMM(BPF_JEQ, BPF_REG_0, 4, 2),
+	BPF_MOV32_IMM(BPF_REG_0, 2),
+	BPF_EXIT_INSN(),
+	/* exit(0); */
+	BPF_MOV32_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
diff --git a/tools/testing/selftests/bpf/verifier/atomic_xor.c b/tools/testing/selftests/bpf/verifier/atomic_xor.c
new file mode 100644
index 000000000000..d1315419a3a8
--- /dev/null
+++ b/tools/testing/selftests/bpf/verifier/atomic_xor.c
@@ -0,0 +1,77 @@
+{
+	"BPF_ATOMIC_XOR without fetch",
+	.insns = {
+		/* val = 0x110; */
+		BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0x110),
+		/* atomic_xor(&val, 0x011); */
+		BPF_MOV64_IMM(BPF_REG_1, 0x011),
+		BPF_ATOMIC_XOR(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
+		/* if (val != 0x101) exit(2); */
+		BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_10, -8),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0x101, 2),
+		BPF_MOV64_IMM(BPF_REG_0, 2),
+		BPF_EXIT_INSN(),
+		/* r1 should not be clobbered, no BPF_FETCH flag */
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0x011, 1),
+		BPF_MOV64_IMM(BPF_REG_0, 1),
+		BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
+{
+	"BPF_ATOMIC_XOR with fetch",
+	.insns = {
+		BPF_MOV64_IMM(BPF_REG_0, 123),
+		/* val = 0x110; */
+		BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0x110),
+		/* old = atomic_fetch_xor(&val, 0x011); */
+		BPF_MOV64_IMM(BPF_REG_1, 0x011),
+		BPF_ATOMIC_FETCH_XOR(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
+		/* if (old != 0x110) exit(3); */
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0x110, 2),
+		BPF_MOV64_IMM(BPF_REG_0, 3),
+		BPF_EXIT_INSN(),
+		/* if (val != 0x101) exit(2); */
+		BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_10, -8),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0x101, 2),
+		BPF_MOV64_IMM(BPF_REG_1, 2),
+		BPF_EXIT_INSN(),
+		/* Check R0 wasn't clobbered (fxor fear of x86 JIT bug) */
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 123, 2),
+		BPF_MOV64_IMM(BPF_REG_0, 1),
+		BPF_EXIT_INSN(),
+		/* exit(0); */
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
+{
+	"BPF_ATOMIC_XOR with fetch 32bit",
+	.insns = {
+		/* r0 = (s64) -1 */
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_ALU64_IMM(BPF_SUB, BPF_REG_0, 1),
+		/* val = 0x110; */
+		BPF_ST_MEM(BPF_W, BPF_REG_10, -4, 0x110),
+		/* old = atomic_fetch_xor(&val, 0x011); */
+		BPF_MOV32_IMM(BPF_REG_1, 0x011),
+		BPF_ATOMIC_FETCH_XOR(BPF_W, BPF_REG_10, BPF_REG_1, -4),
+		/* if (old != 0x110) exit(3); */
+		BPF_JMP32_IMM(BPF_JEQ, BPF_REG_1, 0x110, 2),
+		BPF_MOV32_IMM(BPF_REG_0, 3),
+		BPF_EXIT_INSN(),
+		/* if (val != 0x101) exit(2); */
+		BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_10, -4),
+		BPF_JMP32_IMM(BPF_JEQ, BPF_REG_1, 0x101, 2),
+		BPF_MOV32_IMM(BPF_REG_1, 2),
+		BPF_EXIT_INSN(),
+		/* Check R0 wasn't clobbered (fxor fear of x86 JIT bug)
+		 * It should be -1 so add 1 to get exit code.
+		 */
+		BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 1),
+		BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+},
diff --git a/tools/testing/selftests/bpf/verifier/ctx.c b/tools/testing/selftests/bpf/verifier/ctx.c
index a6d2d82b3447..ede3842d123b 100644
--- a/tools/testing/selftests/bpf/verifier/ctx.c
+++ b/tools/testing/selftests/bpf/verifier/ctx.c
@@ -13,7 +13,7 @@
 	"context stores via BPF_ATOMIC",
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_0, 0),
-	BPF_ATOMIC_ADD(BPF_W, BPF_REG_1, BPF_REG_0, offsetof(struct __sk_buff)),
+	BPF_ATOMIC_ADD(BPF_W, BPF_REG_1, BPF_REG_0, offsetof(struct __sk_buff, mark)),
 	BPF_EXIT_INSN(),
 	},
 	.errstr = "BPF_ATOMIC stores into R1 ctx is not allowed",
-- 
2.29.2.454.gaff20da3a2-goog

Re: [PATCH v2 bpf-next 12/13] bpf: Add tests for new BPF atomic operations

[Yonghong Song]

On 11/27/20 9:57 AM, Brendan Jackman wrote:
> This relies on the work done by Yonghong Song in
> https://reviews.llvm.org/D72184
> 
> Note the hackery in the Makefile that is necessary to avoid breaking
> tests for people who haven't yet got a version of Clang supporting
> V4. It seems like this hackery ought to be confined to
> tools/build/feature - I tried implementing that and found that it
> ballooned into an explosion of nightmares at the top of
> tools/testing/selftests/bpf/Makefile without actually improving the
> clarity of the CLANG_BPF_BUILD_RULE code at all. Hence the simple
> $(shell) call...
> 
> Signed-off-by: Brendan Jackman <jackmanb@google.com>
> ---
>   tools/testing/selftests/bpf/Makefile          |  12 +-
>   .../selftests/bpf/prog_tests/atomics_test.c   | 329 ++++++++++++++++++
>   .../selftests/bpf/progs/atomics_test.c        | 124 +++++++
>   .../selftests/bpf/verifier/atomic_and.c       |  77 ++++
>   .../selftests/bpf/verifier/atomic_cmpxchg.c   |  96 +++++
>   .../selftests/bpf/verifier/atomic_fetch_add.c | 106 ++++++
>   .../selftests/bpf/verifier/atomic_or.c        |  77 ++++
>   .../selftests/bpf/verifier/atomic_sub.c       |  44 +++
>   .../selftests/bpf/verifier/atomic_xchg.c      |  46 +++
>   .../selftests/bpf/verifier/atomic_xor.c       |  77 ++++
>   tools/testing/selftests/bpf/verifier/ctx.c    |   2 +-
>   11 files changed, 987 insertions(+), 3 deletions(-)
>   create mode 100644 tools/testing/selftests/bpf/prog_tests/atomics_test.c
>   create mode 100644 tools/testing/selftests/bpf/progs/atomics_test.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_and.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_fetch_add.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_or.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_sub.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xchg.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xor.c
> 
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 3d5940cd110d..5eadfd09037d 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -228,6 +228,12 @@ IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null | \
>   			grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
>   MENDIAN=$(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
>   
> +# Determine if Clang supports BPF arch v4, and therefore atomics.
> +CLANG_SUPPORTS_V4=$(if $(findstring v4,$(shell $(CLANG) --target=bpf -mcpu=? 2>&1)),true,)
> +ifeq ($(CLANG_SUPPORTS_V4),true)
> +	CFLAGS += -DENABLE_ATOMICS_TESTS
> +endif
> +
>   CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
>   BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN) 			\
>   	     -I$(INCLUDE_DIR) -I$(CURDIR) -I$(APIDIR)			\
> @@ -250,7 +256,9 @@ define CLANG_BPF_BUILD_RULE
>   	$(call msg,CLNG-LLC,$(TRUNNER_BINARY),$2)
>   	$(Q)($(CLANG) $3 -O2 -target bpf -emit-llvm			\
>   		-c $1 -o - || echo "BPF obj compilation failed") | 	\
> -	$(LLC) -mattr=dwarfris -march=bpf -mcpu=v3 $4 -filetype=obj -o $2
> +	$(LLC) -mattr=dwarfris -march=bpf				\
> +		-mcpu=$(if $(CLANG_SUPPORTS_V4),v4,v3)			\
> +		$4 -filetype=obj -o $2
>   endef
>   # Similar to CLANG_BPF_BUILD_RULE, but with disabled alu32
>   define CLANG_NOALU32_BPF_BUILD_RULE
> @@ -391,7 +399,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c trace_helpers.c	\
>   TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read				\
>   		       $(wildcard progs/btf_dump_test_case_*.c)
>   TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
> -TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS)
> +TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS) $(if $(CLANG_SUPPORTS_V4),-DENABLE_ATOMICS_TESTS,)

If the compiler indeed supports cpu v4 (i.e., atomic insns), 
-DENABLE_ATOMICS_TESTS will be added to TRUNNER_BPF_FLAGS and
eventually -DENABLE_ATOMICS_TESTS is also available for
no-alu32 test and this will cause compilation error.

I did the following hack to workaround the issue, i.e., only adds
the definition to default (alu32) test run.

index 5eadfd09037d..3d1320fd93eb 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -230,9 +230,6 @@ MENDIAN=$(if 
$(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)

  # Determine if Clang supports BPF arch v4, and therefore atomics.
  CLANG_SUPPORTS_V4=$(if $(findstring v4,$(shell $(CLANG) --target=bpf 
-mcpu=? 2>&1)),true,)
-ifeq ($(CLANG_SUPPORTS_V4),true)
-       CFLAGS += -DENABLE_ATOMICS_TESTS
-endif

  CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
  BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN)                  \
@@ -255,6 +252,7 @@ $(OUTPUT)/flow_dissector_load.o: flow_dissector_load.h
  define CLANG_BPF_BUILD_RULE
         $(call msg,CLNG-LLC,$(TRUNNER_BINARY),$2)
         $(Q)($(CLANG) $3 -O2 -target bpf -emit-llvm                     \
+               $(if $(CLANG_SUPPORTS_V4),-DENABLE_ATOMICS_TESTS,)      \
                 -c $1 -o - || echo "BPF obj compilation failed") |      \
         $(LLC) -mattr=dwarfris -march=bpf                               \
                 -mcpu=$(if $(CLANG_SUPPORTS_V4),v4,v3)                  \
@@ -399,7 +397,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c 
cgroup_helpers.c trace_helpers.c      \
  TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read                          \
                        $(wildcard progs/btf_dump_test_case_*.c)
  TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
-TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS) $(if 
$(CLANG_SUPPORTS_V4),-DENABLE_ATOMICS_TESTS,)
+TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS)
  TRUNNER_BPF_LDFLAGS := -mattr=+alu32
  $(eval $(call DEFINE_TEST_RUNNER,test_progs))


>   TRUNNER_BPF_LDFLAGS := -mattr=+alu32
>   $(eval $(call DEFINE_TEST_RUNNER,test_progs))
>   
> diff --git a/tools/testing/selftests/bpf/prog_tests/atomics_test.c b/tools/testing/selftests/bpf/prog_tests/atomics_test.c
> new file mode 100644
> index 000000000000..8ecc0392fdf9
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/atomics_test.c
> @@ -0,0 +1,329 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <test_progs.h>
> +
> +#ifdef ENABLE_ATOMICS_TESTS
> +
> +#include "atomics_test.skel.h"
> +
> +static void test_add(void)
[...]
> +
> +#endif /* ENABLE_ATOMICS_TESTS */
> diff --git a/tools/testing/selftests/bpf/progs/atomics_test.c b/tools/testing/selftests/bpf/progs/atomics_test.c
> new file mode 100644
> index 000000000000..3139b00937e5
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/atomics_test.c
> @@ -0,0 +1,124 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +#ifdef ENABLE_ATOMICS_TESTS
> +
> +__u64 add64_value = 1;
> +__u64 add64_result = 0;
> +__u32 add32_value = 1;
> +__u32 add32_result = 0;
> +__u64 add_stack_value_copy = 0;
> +__u64 add_stack_result = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(add, int a)
> +{
> +	__u64 add_stack_value = 1;
> +
> +	add64_result = __sync_fetch_and_add(&add64_value, 2);
> +	add32_result = __sync_fetch_and_add(&add32_value, 2);
> +	add_stack_result = __sync_fetch_and_add(&add_stack_value, 2);
> +	add_stack_value_copy = add_stack_value;
> +
> +	return 0;
> +}
> +
> +__s64 sub64_value = 1;
> +__s64 sub64_result = 0;
> +__s32 sub32_value = 1;
> +__s32 sub32_result = 0;
> +__s64 sub_stack_value_copy = 0;
> +__s64 sub_stack_result = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(sub, int a)
> +{
> +	__u64 sub_stack_value = 1;
> +
> +	sub64_result = __sync_fetch_and_sub(&sub64_value, 2);
> +	sub32_result = __sync_fetch_and_sub(&sub32_value, 2);
> +	sub_stack_result = __sync_fetch_and_sub(&sub_stack_value, 2);
> +	sub_stack_value_copy = sub_stack_value;
> +
> +	return 0;
> +}
> +
> +__u64 and64_value = (0x110ull << 32);
> +__u64 and64_result = 0;
> +__u32 and32_value = 0x110;
> +__u32 and32_result = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(and, int a)
> +{
> +
> +	and64_result = __sync_fetch_and_and(&and64_value, 0x011ull << 32);
> +	and32_result = __sync_fetch_and_and(&and32_value, 0x011);
> +
> +	return 0;
> +}
> +
> +__u64 or64_value = (0x110ull << 32);
> +__u64 or64_result = 0;
> +__u32 or32_value = 0x110;
> +__u32 or32_result = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(or, int a)
> +{
> +	or64_result = __sync_fetch_and_or(&or64_value, 0x011ull << 32);
> +	or32_result = __sync_fetch_and_or(&or32_value, 0x011);
> +
> +	return 0;
> +}
> +
> +__u64 xor64_value = (0x110ull << 32);
> +__u64 xor64_result = 0;
> +__u32 xor32_value = 0x110;
> +__u32 xor32_result = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(xor, int a)
> +{
> +	xor64_result = __sync_fetch_and_xor(&xor64_value, 0x011ull << 32);
> +	xor32_result = __sync_fetch_and_xor(&xor32_value, 0x011);
> +
> +	return 0;
> +}

All above __sync_fetch_and_{add, sub, and, or, xor} produces a return
value used later. To test atomic_<op> instructions, it will be good if
you can add some tests which ignores the return value.

> +
> +__u64 cmpxchg64_value = 1;
> +__u64 cmpxchg64_result_fail = 0;
> +__u64 cmpxchg64_result_succeed = 0;
> +__u32 cmpxchg32_value = 1;
> +__u32 cmpxchg32_result_fail = 0;
> +__u32 cmpxchg32_result_succeed = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(cmpxchg, int a)
> +{
> +	cmpxchg64_result_fail = __sync_val_compare_and_swap(
> +		&cmpxchg64_value, 0, 3);
> +	cmpxchg64_result_succeed = __sync_val_compare_and_swap(
> +		&cmpxchg64_value, 1, 2);
> +
> +	cmpxchg32_result_fail = __sync_val_compare_and_swap(
> +		&cmpxchg32_value, 0, 3);
> +	cmpxchg32_result_succeed = __sync_val_compare_and_swap(
> +		&cmpxchg32_value, 1, 2);
> +
> +	return 0;
> +}
> +
> +__u64 xchg64_value = 1;
> +__u64 xchg64_result = 0;
> +__u32 xchg32_value = 1;
> +__u32 xchg32_result = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(xchg, int a)
> +{
> +	__u64 val64 = 2;
> +	__u32 val32 = 2;
> +
> +	__atomic_exchange(&xchg64_value, &val64, &xchg64_result, __ATOMIC_RELAXED);
> +	__atomic_exchange(&xchg32_value, &val32, &xchg32_result, __ATOMIC_RELAXED);
> +
> +	return 0;
> +}
> +
> +#endif /* ENABLE_ATOMICS_TESTS */
[...]

Re: [PATCH v2 bpf-next 12/13] bpf: Add tests for new BPF atomic operations

[Brendan Jackman]

On Mon, Nov 30, 2020 at 07:55:02PM -0800, Yonghong Song wrote:
> On 11/27/20 9:57 AM, Brendan Jackman wrote:
[...]
> > diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> > index 3d5940cd110d..5eadfd09037d 100644
> > --- a/tools/testing/selftests/bpf/Makefile
> > +++ b/tools/testing/selftests/bpf/Makefile
> > @@ -228,6 +228,12 @@ IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null | \
> >   			grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
> >   MENDIAN=$(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
> > +# Determine if Clang supports BPF arch v4, and therefore atomics.
> > +CLANG_SUPPORTS_V4=$(if $(findstring v4,$(shell $(CLANG) --target=bpf -mcpu=? 2>&1)),true,)
> > +ifeq ($(CLANG_SUPPORTS_V4),true)
> > +	CFLAGS += -DENABLE_ATOMICS_TESTS
> > +endif
> > +
> >   CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
> >   BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN) 			\
> >   	     -I$(INCLUDE_DIR) -I$(CURDIR) -I$(APIDIR)			\
> > @@ -250,7 +256,9 @@ define CLANG_BPF_BUILD_RULE
> >   	$(call msg,CLNG-LLC,$(TRUNNER_BINARY),$2)
> >   	$(Q)($(CLANG) $3 -O2 -target bpf -emit-llvm			\
> >   		-c $1 -o - || echo "BPF obj compilation failed") | 	\
> > -	$(LLC) -mattr=dwarfris -march=bpf -mcpu=v3 $4 -filetype=obj -o $2
> > +	$(LLC) -mattr=dwarfris -march=bpf				\
> > +		-mcpu=$(if $(CLANG_SUPPORTS_V4),v4,v3)			\
> > +		$4 -filetype=obj -o $2
> >   endef
> >   # Similar to CLANG_BPF_BUILD_RULE, but with disabled alu32
> >   define CLANG_NOALU32_BPF_BUILD_RULE
> > @@ -391,7 +399,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c trace_helpers.c	\
> >   TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read				\
> >   		       $(wildcard progs/btf_dump_test_case_*.c)
> >   TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
> > -TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS)
> > +TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS) $(if $(CLANG_SUPPORTS_V4),-DENABLE_ATOMICS_TESTS,)
> 
> If the compiler indeed supports cpu v4 (i.e., atomic insns),
> -DENABLE_ATOMICS_TESTS will be added to TRUNNER_BPF_FLAGS and
> eventually -DENABLE_ATOMICS_TESTS is also available for
> no-alu32 test and this will cause compilation error.
> 
> I did the following hack to workaround the issue, i.e., only adds
> the definition to default (alu32) test run.
> 
> index 5eadfd09037d..3d1320fd93eb 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -230,9 +230,6 @@ MENDIAN=$(if
> $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
> 
>  # Determine if Clang supports BPF arch v4, and therefore atomics.
>  CLANG_SUPPORTS_V4=$(if $(findstring v4,$(shell $(CLANG) --target=bpf
> -mcpu=? 2>&1)),true,)
> -ifeq ($(CLANG_SUPPORTS_V4),true)
> -       CFLAGS += -DENABLE_ATOMICS_TESTS
> -endif
> 
>  CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
>  BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN)                  \
> @@ -255,6 +252,7 @@ $(OUTPUT)/flow_dissector_load.o: flow_dissector_load.h
>  define CLANG_BPF_BUILD_RULE
>         $(call msg,CLNG-LLC,$(TRUNNER_BINARY),$2)
>         $(Q)($(CLANG) $3 -O2 -target bpf -emit-llvm                     \
> +               $(if $(CLANG_SUPPORTS_V4),-DENABLE_ATOMICS_TESTS,)      \
>                 -c $1 -o - || echo "BPF obj compilation failed") |      \
>         $(LLC) -mattr=dwarfris -march=bpf                               \
>                 -mcpu=$(if $(CLANG_SUPPORTS_V4),v4,v3)                  \
> @@ -399,7 +397,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c
> trace_helpers.c      \
>  TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read                          \
>                        $(wildcard progs/btf_dump_test_case_*.c)
>  TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
> -TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS) $(if
> $(CLANG_SUPPORTS_V4),-DENABLE_ATOMICS_TESTS,)
> +TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS)
>  TRUNNER_BPF_LDFLAGS := -mattr=+alu32
>  $(eval $(call DEFINE_TEST_RUNNER,test_progs))

Ah, good point. I think your "hack" actually improves the overall result
anyway since it avoids the akward global mutation of CFLAGS. Thanks!

I wonder if we should actually have Clang define a built-in macro to say
that the atomics are supported?

> > diff --git a/tools/testing/selftests/bpf/prog_tests/atomics_test.c b/tools/testing/selftests/bpf/prog_tests/atomics_test.c
> > new file mode 100644
> > index 000000000000..8ecc0392fdf9
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/prog_tests/atomics_test.c
> > @@ -0,0 +1,329 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <test_progs.h>
> > +
> > +#ifdef ENABLE_ATOMICS_TESTS
> > +
> > +#include "atomics_test.skel.h"
> > +
> > +static void test_add(void)
> [...]
> > +
> > +#endif /* ENABLE_ATOMICS_TESTS */
> > diff --git a/tools/testing/selftests/bpf/progs/atomics_test.c b/tools/testing/selftests/bpf/progs/atomics_test.c
[...]
> > +__u64 xor64_value = (0x110ull << 32);
> > +__u64 xor64_result = 0;
> > +__u32 xor32_value = 0x110;
> > +__u32 xor32_result = 0;
> > +SEC("fentry/bpf_fentry_test1")
> > +int BPF_PROG(xor, int a)
> > +{
> > +	xor64_result = __sync_fetch_and_xor(&xor64_value, 0x011ull << 32);
> > +	xor32_result = __sync_fetch_and_xor(&xor32_value, 0x011);
> > +
> > +	return 0;
> > +}
> 
> All above __sync_fetch_and_{add, sub, and, or, xor} produces a return
> value used later. To test atomic_<op> instructions, it will be good if
> you can add some tests which ignores the return value.

Good idea - adding an extra case to each prog. This won't assert that
LLVM is generating "optimal" code (without BPF_FETCH) but we can at
least get some confidence we aren't generating total garbage.

Re: [PATCH v2 bpf-next 12/13] bpf: Add tests for new BPF atomic operations

[Yonghong Song]

On 12/1/20 4:56 AM, Brendan Jackman wrote:
> On Mon, Nov 30, 2020 at 07:55:02PM -0800, Yonghong Song wrote:
>> On 11/27/20 9:57 AM, Brendan Jackman wrote:
> [...]
>>> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
>>> index 3d5940cd110d..5eadfd09037d 100644
>>> --- a/tools/testing/selftests/bpf/Makefile
>>> +++ b/tools/testing/selftests/bpf/Makefile
>>> @@ -228,6 +228,12 @@ IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null | \
>>>    			grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
>>>    MENDIAN=$(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
>>> +# Determine if Clang supports BPF arch v4, and therefore atomics.
>>> +CLANG_SUPPORTS_V4=$(if $(findstring v4,$(shell $(CLANG) --target=bpf -mcpu=? 2>&1)),true,)
>>> +ifeq ($(CLANG_SUPPORTS_V4),true)
>>> +	CFLAGS += -DENABLE_ATOMICS_TESTS
>>> +endif
>>> +
>>>    CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
>>>    BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN) 			\
>>>    	     -I$(INCLUDE_DIR) -I$(CURDIR) -I$(APIDIR)			\
>>> @@ -250,7 +256,9 @@ define CLANG_BPF_BUILD_RULE
>>>    	$(call msg,CLNG-LLC,$(TRUNNER_BINARY),$2)
>>>    	$(Q)($(CLANG) $3 -O2 -target bpf -emit-llvm			\
>>>    		-c $1 -o - || echo "BPF obj compilation failed") | 	\
>>> -	$(LLC) -mattr=dwarfris -march=bpf -mcpu=v3 $4 -filetype=obj -o $2
>>> +	$(LLC) -mattr=dwarfris -march=bpf				\
>>> +		-mcpu=$(if $(CLANG_SUPPORTS_V4),v4,v3)			\
>>> +		$4 -filetype=obj -o $2
>>>    endef
>>>    # Similar to CLANG_BPF_BUILD_RULE, but with disabled alu32
>>>    define CLANG_NOALU32_BPF_BUILD_RULE
>>> @@ -391,7 +399,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c trace_helpers.c	\
>>>    TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read				\
>>>    		       $(wildcard progs/btf_dump_test_case_*.c)
>>>    TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
>>> -TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS)
>>> +TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS) $(if $(CLANG_SUPPORTS_V4),-DENABLE_ATOMICS_TESTS,)
>>
>> If the compiler indeed supports cpu v4 (i.e., atomic insns),
>> -DENABLE_ATOMICS_TESTS will be added to TRUNNER_BPF_FLAGS and
>> eventually -DENABLE_ATOMICS_TESTS is also available for
>> no-alu32 test and this will cause compilation error.
>>
>> I did the following hack to workaround the issue, i.e., only adds
>> the definition to default (alu32) test run.
>>
>> index 5eadfd09037d..3d1320fd93eb 100644
>> --- a/tools/testing/selftests/bpf/Makefile
>> +++ b/tools/testing/selftests/bpf/Makefile
>> @@ -230,9 +230,6 @@ MENDIAN=$(if
>> $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
>>
>>   # Determine if Clang supports BPF arch v4, and therefore atomics.
>>   CLANG_SUPPORTS_V4=$(if $(findstring v4,$(shell $(CLANG) --target=bpf
>> -mcpu=? 2>&1)),true,)
>> -ifeq ($(CLANG_SUPPORTS_V4),true)
>> -       CFLAGS += -DENABLE_ATOMICS_TESTS
>> -endif
>>
>>   CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
>>   BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN)                  \
>> @@ -255,6 +252,7 @@ $(OUTPUT)/flow_dissector_load.o: flow_dissector_load.h
>>   define CLANG_BPF_BUILD_RULE
>>          $(call msg,CLNG-LLC,$(TRUNNER_BINARY),$2)
>>          $(Q)($(CLANG) $3 -O2 -target bpf -emit-llvm                     \
>> +               $(if $(CLANG_SUPPORTS_V4),-DENABLE_ATOMICS_TESTS,)      \
>>                  -c $1 -o - || echo "BPF obj compilation failed") |      \
>>          $(LLC) -mattr=dwarfris -march=bpf                               \
>>                  -mcpu=$(if $(CLANG_SUPPORTS_V4),v4,v3)                  \
>> @@ -399,7 +397,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c
>> trace_helpers.c      \
>>   TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read                          \
>>                         $(wildcard progs/btf_dump_test_case_*.c)
>>   TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
>> -TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS) $(if
>> $(CLANG_SUPPORTS_V4),-DENABLE_ATOMICS_TESTS,)
>> +TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS)
>>   TRUNNER_BPF_LDFLAGS := -mattr=+alu32
>>   $(eval $(call DEFINE_TEST_RUNNER,test_progs))
> 
> Ah, good point. I think your "hack" actually improves the overall result
> anyway since it avoids the akward global mutation of CFLAGS. Thanks!
> 
> I wonder if we should actually have Clang define a built-in macro to say
> that the atomics are supported?

We are using gcc builtin's and they are all supported by clang, so
"#if __has_builtin(__sync_fetch_and_or)" is always true so it
won't work here.

We could add a macro like __BPF_ATOMICS_SUPPORTED__ in clang.
But you still need a checking to decide whether to use -mcpu=v4. If
you have that information, it will be trivial to add your
own macros if it is -mcpu=v4.

> 
>>> diff --git a/tools/testing/selftests/bpf/prog_tests/atomics_test.c b/tools/testing/selftests/bpf/prog_tests/atomics_test.c
>>> new file mode 100644
>>> index 000000000000..8ecc0392fdf9
>>> --- /dev/null
>>> +++ b/tools/testing/selftests/bpf/prog_tests/atomics_test.c
>>> @@ -0,0 +1,329 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +
>>> +#include <test_progs.h>
>>> +
>>> +#ifdef ENABLE_ATOMICS_TESTS
>>> +
>>> +#include "atomics_test.skel.h"
>>> +
>>> +static void test_add(void)
>> [...]
>>> +
>>> +#endif /* ENABLE_ATOMICS_TESTS */
>>> diff --git a/tools/testing/selftests/bpf/progs/atomics_test.c b/tools/testing/selftests/bpf/progs/atomics_test.c
> [...]
>>> +__u64 xor64_value = (0x110ull << 32);
>>> +__u64 xor64_result = 0;
>>> +__u32 xor32_value = 0x110;
>>> +__u32 xor32_result = 0;
>>> +SEC("fentry/bpf_fentry_test1")
>>> +int BPF_PROG(xor, int a)
>>> +{
>>> +	xor64_result = __sync_fetch_and_xor(&xor64_value, 0x011ull << 32);
>>> +	xor32_result = __sync_fetch_and_xor(&xor32_value, 0x011);
>>> +
>>> +	return 0;
>>> +}
>>
>> All above __sync_fetch_and_{add, sub, and, or, xor} produces a return
>> value used later. To test atomic_<op> instructions, it will be good if
>> you can add some tests which ignores the return value.
> 
> Good idea - adding an extra case to each prog. This won't assert that
> LLVM is generating "optimal" code (without BPF_FETCH) but we can at
> least get some confidence we aren't generating total garbage.
> 

Re: [PATCH v2 bpf-next 12/13] bpf: Add tests for new BPF atomic operations

[Andrii Nakryiko]

On Fri, Nov 27, 2020 at 10:01 AM Brendan Jackman <jackmanb@google.com> wrote:
>
> This relies on the work done by Yonghong Song in
> https://reviews.llvm.org/D72184
>
> Note the hackery in the Makefile that is necessary to avoid breaking
> tests for people who haven't yet got a version of Clang supporting
> V4. It seems like this hackery ought to be confined to
> tools/build/feature - I tried implementing that and found that it
> ballooned into an explosion of nightmares at the top of
> tools/testing/selftests/bpf/Makefile without actually improving the
> clarity of the CLANG_BPF_BUILD_RULE code at all. Hence the simple
> $(shell) call...
>
> Signed-off-by: Brendan Jackman <jackmanb@google.com>
> ---
>  tools/testing/selftests/bpf/Makefile          |  12 +-
>  .../selftests/bpf/prog_tests/atomics_test.c   | 329 ++++++++++++++++++
>  .../selftests/bpf/progs/atomics_test.c        | 124 +++++++
>  .../selftests/bpf/verifier/atomic_and.c       |  77 ++++
>  .../selftests/bpf/verifier/atomic_cmpxchg.c   |  96 +++++
>  .../selftests/bpf/verifier/atomic_fetch_add.c | 106 ++++++
>  .../selftests/bpf/verifier/atomic_or.c        |  77 ++++
>  .../selftests/bpf/verifier/atomic_sub.c       |  44 +++
>  .../selftests/bpf/verifier/atomic_xchg.c      |  46 +++
>  .../selftests/bpf/verifier/atomic_xor.c       |  77 ++++
>  tools/testing/selftests/bpf/verifier/ctx.c    |   2 +-
>  11 files changed, 987 insertions(+), 3 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/atomics_test.c
>  create mode 100644 tools/testing/selftests/bpf/progs/atomics_test.c
>  create mode 100644 tools/testing/selftests/bpf/verifier/atomic_and.c
>  create mode 100644 tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c
>  create mode 100644 tools/testing/selftests/bpf/verifier/atomic_fetch_add.c
>  create mode 100644 tools/testing/selftests/bpf/verifier/atomic_or.c
>  create mode 100644 tools/testing/selftests/bpf/verifier/atomic_sub.c
>  create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xchg.c
>  create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xor.c
>
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 3d5940cd110d..5eadfd09037d 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -228,6 +228,12 @@ IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null | \
>                         grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
>  MENDIAN=$(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
>
> +# Determine if Clang supports BPF arch v4, and therefore atomics.
> +CLANG_SUPPORTS_V4=$(if $(findstring v4,$(shell $(CLANG) --target=bpf -mcpu=? 2>&1)),true,)
> +ifeq ($(CLANG_SUPPORTS_V4),true)
> +       CFLAGS += -DENABLE_ATOMICS_TESTS
> +endif
> +
>  CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
>  BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN)                  \
>              -I$(INCLUDE_DIR) -I$(CURDIR) -I$(APIDIR)                   \
> @@ -250,7 +256,9 @@ define CLANG_BPF_BUILD_RULE
>         $(call msg,CLNG-LLC,$(TRUNNER_BINARY),$2)
>         $(Q)($(CLANG) $3 -O2 -target bpf -emit-llvm                     \
>                 -c $1 -o - || echo "BPF obj compilation failed") |      \
> -       $(LLC) -mattr=dwarfris -march=bpf -mcpu=v3 $4 -filetype=obj -o $2
> +       $(LLC) -mattr=dwarfris -march=bpf                               \
> +               -mcpu=$(if $(CLANG_SUPPORTS_V4),v4,v3)                  \
> +               $4 -filetype=obj -o $2
>  endef
>  # Similar to CLANG_BPF_BUILD_RULE, but with disabled alu32
>  define CLANG_NOALU32_BPF_BUILD_RULE
> @@ -391,7 +399,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c trace_helpers.c      \
>  TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read                          \
>                        $(wildcard progs/btf_dump_test_case_*.c)
>  TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
> -TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS)
> +TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS) $(if $(CLANG_SUPPORTS_V4),-DENABLE_ATOMICS_TESTS,)
>  TRUNNER_BPF_LDFLAGS := -mattr=+alu32
>  $(eval $(call DEFINE_TEST_RUNNER,test_progs))
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/atomics_test.c b/tools/testing/selftests/bpf/prog_tests/atomics_test.c
> new file mode 100644
> index 000000000000..8ecc0392fdf9
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/atomics_test.c
> @@ -0,0 +1,329 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <test_progs.h>
> +
> +#ifdef ENABLE_ATOMICS_TESTS
> +
> +#include "atomics_test.skel.h"
> +

[...]

> +
> +static void test_xchg(void)
> +{
> +       struct atomics_test *atomics_skel = NULL;

nit: = NULL is unnecessary

> +       int err, prog_fd;
> +       __u32 duration = 0, retval;
> +
> +       atomics_skel = atomics_test__open_and_load();
> +       if (CHECK(!atomics_skel, "atomics_skel_load", "atomics skeleton failed\n"))
> +               goto cleanup;
> +
> +       err = atomics_test__attach(atomics_skel);
> +       if (CHECK(err, "atomics_attach", "atomics attach failed: %d\n", err))
> +               goto cleanup;
> +
> +       prog_fd = bpf_program__fd(atomics_skel->progs.add);
> +       err = bpf_prog_test_run(prog_fd, 1, NULL, 0,
> +                               NULL, NULL, &retval, &duration);
> +       if (CHECK(err || retval, "test_run add",
> +                 "err %d errno %d retval %d duration %d\n",
> +                 err, errno, retval, duration))
> +               goto cleanup;
> +
> +       CHECK(atomics_skel->data->xchg64_value != 2, "xchg64_value",
> +             "64bit xchg left unexpected value (got %lld want 2)\n",
> +             atomics_skel->data->xchg64_value);
> +       CHECK(atomics_skel->bss->xchg64_result != 1, "xchg_result",
> +             "64bit xchg returned bad result (got %lld want 1)\n",
> +             atomics_skel->bss->xchg64_result);
> +
> +       CHECK(atomics_skel->data->xchg32_value != 2, "xchg32_value",
> +             "32bit xchg left unexpected value (got %d want 2)\n",
> +             atomics_skel->data->xchg32_value);
> +       CHECK(atomics_skel->bss->xchg32_result != 1, "xchg_result",
> +             "32bit xchg returned bad result (got %d want 1)\n",
> +             atomics_skel->bss->xchg32_result);

ASSERT_EQ() is less verbose.

> +
> +cleanup:
> +       atomics_test__destroy(atomics_skel);
> +}
> +
> +void test_atomics_test(void)
> +{

why the gigantic #ifdef/#else block if you could do the check here,
skip and exit?

> +       test_add();
> +       test_sub();
> +       test_and();
> +       test_or();
> +       test_xor();
> +       test_cmpxchg();
> +       test_xchg();


please model these as sub-tests, it will be easier to debug, if anything

> +}
> +
> +#else /* ENABLE_ATOMICS_TESTS */
> +
> +void test_atomics_test(void)
> +{
> +       printf("%s:SKIP:no ENABLE_ATOMICS_TEST (missing Clang BPF atomics support)",
> +              __func__);
> +       test__skip();
> +}
> +
> +#endif /* ENABLE_ATOMICS_TESTS */
> diff --git a/tools/testing/selftests/bpf/progs/atomics_test.c b/tools/testing/selftests/bpf/progs/atomics_test.c
> new file mode 100644
> index 000000000000..3139b00937e5
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/atomics_test.c
> @@ -0,0 +1,124 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +#ifdef ENABLE_ATOMICS_TESTS
> +
> +__u64 add64_value = 1;
> +__u64 add64_result = 0;
> +__u32 add32_value = 1;
> +__u32 add32_result = 0;
> +__u64 add_stack_value_copy = 0;
> +__u64 add_stack_result = 0;

empty line here

> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(add, int a)
> +{
> +       __u64 add_stack_value = 1;
> +
> +       add64_result = __sync_fetch_and_add(&add64_value, 2);
> +       add32_result = __sync_fetch_and_add(&add32_value, 2);
> +       add_stack_result = __sync_fetch_and_add(&add_stack_value, 2);
> +       add_stack_value_copy = add_stack_value;
> +
> +       return 0;
> +}
> +
> +__s64 sub64_value = 1;
> +__s64 sub64_result = 0;
> +__s32 sub32_value = 1;
> +__s32 sub32_result = 0;
> +__s64 sub_stack_value_copy = 0;
> +__s64 sub_stack_result = 0;

same

> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(sub, int a)
> +{
> +       __u64 sub_stack_value = 1;
> +
> +       sub64_result = __sync_fetch_and_sub(&sub64_value, 2);
> +       sub32_result = __sync_fetch_and_sub(&sub32_value, 2);
> +       sub_stack_result = __sync_fetch_and_sub(&sub_stack_value, 2);
> +       sub_stack_value_copy = sub_stack_value;
> +
> +       return 0;
> +}
> +
> +__u64 and64_value = (0x110ull << 32);
> +__u64 and64_result = 0;
> +__u32 and32_value = 0x110;
> +__u32 and32_result = 0;

yep

> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(and, int a)
> +{
> +
> +       and64_result = __sync_fetch_and_and(&and64_value, 0x011ull << 32);
> +       and32_result = __sync_fetch_and_and(&and32_value, 0x011);
> +
> +       return 0;
> +}
> +
> +__u64 or64_value = (0x110ull << 32);
> +__u64 or64_result = 0;
> +__u32 or32_value = 0x110;
> +__u32 or32_result = 0;

here too

> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(or, int a)
> +{
> +       or64_result = __sync_fetch_and_or(&or64_value, 0x011ull << 32);
> +       or32_result = __sync_fetch_and_or(&or32_value, 0x011);
> +
> +       return 0;
> +}
> +
> +__u64 xor64_value = (0x110ull << 32);
> +__u64 xor64_result = 0;
> +__u32 xor32_value = 0x110;
> +__u32 xor32_result = 0;

you get the idea... How often do you define global variables in
user-space code right next to the function without an extra line
between them?..

> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(xor, int a)
> +{
> +       xor64_result = __sync_fetch_and_xor(&xor64_value, 0x011ull << 32);
> +       xor32_result = __sync_fetch_and_xor(&xor32_value, 0x011);
> +
> +       return 0;
> +}
> +
> +__u64 cmpxchg64_value = 1;
> +__u64 cmpxchg64_result_fail = 0;
> +__u64 cmpxchg64_result_succeed = 0;
> +__u32 cmpxchg32_value = 1;
> +__u32 cmpxchg32_result_fail = 0;
> +__u32 cmpxchg32_result_succeed = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(cmpxchg, int a)
> +{
> +       cmpxchg64_result_fail = __sync_val_compare_and_swap(
> +               &cmpxchg64_value, 0, 3);
> +       cmpxchg64_result_succeed = __sync_val_compare_and_swap(
> +               &cmpxchg64_value, 1, 2);
> +
> +       cmpxchg32_result_fail = __sync_val_compare_and_swap(
> +               &cmpxchg32_value, 0, 3);
> +       cmpxchg32_result_succeed = __sync_val_compare_and_swap(
> +               &cmpxchg32_value, 1, 2);

single lines are fine here and much more readable

> +
> +       return 0;
> +}
> +
> +__u64 xchg64_value = 1;
> +__u64 xchg64_result = 0;
> +__u32 xchg32_value = 1;
> +__u32 xchg32_result = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(xchg, int a)
> +{
> +       __u64 val64 = 2;
> +       __u32 val32 = 2;
> +
> +       __atomic_exchange(&xchg64_value, &val64, &xchg64_result, __ATOMIC_RELAXED);
> +       __atomic_exchange(&xchg32_value, &val32, &xchg32_result, __ATOMIC_RELAXED);
> +
> +       return 0;
> +}
> +
> +#endif /* ENABLE_ATOMICS_TESTS */

[...]

Re: [PATCH v2 bpf-next 12/13] bpf: Add tests for new BPF atomic operations

[Brendan Jackman]

On Tue, Dec 01, 2020 at 06:22:50PM -0800, Andrii Nakryiko wrote:
> On Fri, Nov 27, 2020 at 10:01 AM Brendan Jackman <jackmanb@google.com> wrote:
[...]
> > +
> > +static void test_xchg(void)
> > +{
> > +       struct atomics_test *atomics_skel = NULL;
> 
> nit: = NULL is unnecessary
[...[
> > +       CHECK(atomics_skel->data->xchg32_value != 2, "xchg32_value",
> > +             "32bit xchg left unexpected value (got %d want 2)\n",
> > +             atomics_skel->data->xchg32_value);
> > +       CHECK(atomics_skel->bss->xchg32_result != 1, "xchg_result",
> > +             "32bit xchg returned bad result (got %d want 1)\n",
> > +             atomics_skel->bss->xchg32_result);
> 
> ASSERT_EQ() is less verbose.
> 
> > +
> > +cleanup:
> > +       atomics_test__destroy(atomics_skel);
> > +}
> > +
> > +void test_atomics_test(void)
> > +{
> 
> why the gigantic #ifdef/#else block if you could do the check here,
> skip and exit?
> 
> > +       test_add();
> > +       test_sub();
> > +       test_and();
> > +       test_or();
> > +       test_xor();
> > +       test_cmpxchg();
> > +       test_xchg();
> 
> 
> please model these as sub-tests, it will be easier to debug, if anything
> 
> > +}
> > +
> > +#else /* ENABLE_ATOMICS_TESTS */
> > +
> > +void test_atomics_test(void)
> > +{
> > +       printf("%s:SKIP:no ENABLE_ATOMICS_TEST (missing Clang BPF atomics support)",
> > +              __func__);
> > +       test__skip();
> > +}
> > +
> > +#endif /* ENABLE_ATOMICS_TESTS */
> > diff --git a/tools/testing/selftests/bpf/progs/atomics_test.c b/tools/testing/selftests/bpf/progs/atomics_test.c
> > new file mode 100644
> > index 000000000000..3139b00937e5
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/atomics_test.c
> > @@ -0,0 +1,124 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include <linux/bpf.h>
> > +#include <bpf/bpf_helpers.h>
> > +#include <bpf/bpf_tracing.h>
> > +
> > +#ifdef ENABLE_ATOMICS_TESTS
> > +
> > +__u64 add64_value = 1;
> > +__u64 add64_result = 0;
> > +__u32 add32_value = 1;
> > +__u32 add32_result = 0;
> > +__u64 add_stack_value_copy = 0;
> > +__u64 add_stack_result = 0;
> 
> empty line here
> 
> > +SEC("fentry/bpf_fentry_test1")
> > +int BPF_PROG(add, int a)
> > +{
> > +       __u64 add_stack_value = 1;
> > +
> > +       add64_result = __sync_fetch_and_add(&add64_value, 2);
> > +       add32_result = __sync_fetch_and_add(&add32_value, 2);
> > +       add_stack_result = __sync_fetch_and_add(&add_stack_value, 2);
> > +       add_stack_value_copy = add_stack_value;
> > +
> > +       return 0;
> > +}
> > +
> > +__s64 sub64_value = 1;
> > +__s64 sub64_result = 0;
> > +__s32 sub32_value = 1;
> > +__s32 sub32_result = 0;
> > +__s64 sub_stack_value_copy = 0;
> > +__s64 sub_stack_result = 0;
> 
> same
> 
> > +SEC("fentry/bpf_fentry_test1")
> > +int BPF_PROG(sub, int a)
> > +{
> > +       __u64 sub_stack_value = 1;
> > +
> > +       sub64_result = __sync_fetch_and_sub(&sub64_value, 2);
> > +       sub32_result = __sync_fetch_and_sub(&sub32_value, 2);
> > +       sub_stack_result = __sync_fetch_and_sub(&sub_stack_value, 2);
> > +       sub_stack_value_copy = sub_stack_value;
> > +
> > +       return 0;
> > +}
> > +
> > +__u64 and64_value = (0x110ull << 32);
> > +__u64 and64_result = 0;
> > +__u32 and32_value = 0x110;
> > +__u32 and32_result = 0;
> 
> yep
> 
> > +SEC("fentry/bpf_fentry_test1")
> > +int BPF_PROG(and, int a)
> > +{
> > +
> > +       and64_result = __sync_fetch_and_and(&and64_value, 0x011ull << 32);
> > +       and32_result = __sync_fetch_and_and(&and32_value, 0x011);
> > +
> > +       return 0;
> > +}
> > +
> > +__u64 or64_value = (0x110ull << 32);
> > +__u64 or64_result = 0;
> > +__u32 or32_value = 0x110;
> > +__u32 or32_result = 0;
> 
> here too
> 
> > +SEC("fentry/bpf_fentry_test1")
> > +int BPF_PROG(or, int a)
> > +{
> > +       or64_result = __sync_fetch_and_or(&or64_value, 0x011ull << 32);
> > +       or32_result = __sync_fetch_and_or(&or32_value, 0x011);
> > +
> > +       return 0;
> > +}
> > +
> > +__u64 xor64_value = (0x110ull << 32);
> > +__u64 xor64_result = 0;
> > +__u32 xor32_value = 0x110;
> > +__u32 xor32_result = 0;
> 
> you get the idea... How often do you define global variables in
> user-space code right next to the function without an extra line
> between them?..
> 
[...]
> > +       cmpxchg64_result_succeed = __sync_val_compare_and_swap(
> > +               &cmpxchg64_value, 1, 2);
> > +
> > +       cmpxchg32_result_fail = __sync_val_compare_and_swap(
> > +               &cmpxchg32_value, 0, 3);
> > +       cmpxchg32_result_succeed = __sync_val_compare_and_swap(
> > +               &cmpxchg32_value, 1, 2);
> 
> single lines are fine here and much more readable

Thanks, ack to all comments.

[PATCH v2 bpf-next 13/13] bpf: Document new atomic instructions

[Brendan Jackman]

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 Documentation/networking/filter.rst | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst
index 1583d59d806d..c86091b8cb0e 100644
--- a/Documentation/networking/filter.rst
+++ b/Documentation/networking/filter.rst
@@ -1053,6 +1053,33 @@ encoding.
    .imm = BPF_ADD, .code = BPF_ATOMIC | BPF_W  | BPF_STX: lock xadd *(u32 *)(dst_reg + off16) += src_reg
    .imm = BPF_ADD, .code = BPF_ATOMIC | BPF_DW | BPF_STX: lock xadd *(u64 *)(dst_reg + off16) += src_reg
 
+The basic atomic operations supported (from architecture v4 onwards) are:
+
+    BPF_ADD
+    BPF_SUB
+    BPF_AND
+    BPF_OR
+    BPF_XOR
+
+Each having isomorphic semantics with the ``BPF_ADD`` example, that is: the
+memory location addresed by ``dst_reg + off`` is atomically modified, with
+``src_reg`` as the other operand. If the ``BPF_FETCH`` flag is set in the
+immediate, then these operations also overwrite ``src_reg`` with the
+pre-modification value from memory.
+
+The more special operations are:
+
+    BPF_XCHG
+
+This atomically exchanges ``src_reg`` with the value addressed by ``dst_reg +
+off``.
+
+    BPF_CMPXCHG
+
+This atomically compares the value addressed by ``dst_reg + off`` with
+``R0``. If they match it is replaced with ``src_reg``, The pre-modification
+value is loaded back to ``R0``.
+
 Note that 1 and 2 byte atomic operations are not supported.
 
 You may encounter BPF_XADD - this is a legacy name for BPF_ATOMIC, referring to
-- 
2.29.2.454.gaff20da3a2-goog

Re: [PATCH v2 bpf-next 00/13] Atomics for eBPF

[Yonghong Song]

On 11/27/20 9:57 AM, Brendan Jackman wrote:
> Status of the patches
> =====================
> 
> Thanks for the reviews! Differences from v1->v2 [1]:
> 
> * Fixed mistakes in the netronome driver
> 
> * Addd sub, add, or, xor operations
> 
> * The above led to some refactors to keep things readable. (Maybe I
>    should have just waited until I'd implemented these before starting
>    the review...)
> 
> * Replaced BPF_[CMP]SET | BPF_FETCH with just BPF_[CMP]XCHG, which
>    include the BPF_FETCH flag
> 
> * Added a bit of documentation. Suggestions welcome for more places
>    to dump this info...
> 
> The prog_test that's added depends on Clang/LLVM features added by
> Yonghong in https://reviews.llvm.org/D72184
> 
> This only includes a JIT implementation for x86_64 - I don't plan to
> implement JIT support myself for other architectures.
> 
> Operations
> ==========
> 
> This patchset adds atomic operations to the eBPF instruction set. The
> use-case that motivated this work was a trivial and efficient way to
> generate globally-unique cookies in BPF progs, but I think it's
> obvious that these features are pretty widely applicable.  The
> instructions that are added here can be summarised with this list of
> kernel operations:
> 
> * atomic[64]_[fetch_]add
> * atomic[64]_[fetch_]sub
> * atomic[64]_[fetch_]and
> * atomic[64]_[fetch_]or

* atomic[64]_[fetch_]xor

> * atomic[64]_xchg
> * atomic[64]_cmpxchg

Thanks. Overall looks good to me but I did not check carefully
on jit part as I am not an expert in x64 assembly...

This patch also introduced atomic[64]_{sub,and,or,xor}, similar to
xadd. I am not sure whether it is necessary. For one thing,
users can just use atomic[64]_fetch_{sub,and,or,xor} to ignore
return value and they will achieve the same result, right?
 From llvm side, there is no ready-to-use gcc builtin matching
atomic[64]_{sub,and,or,xor} which does not have return values.
If we go this route, we will need to invent additional bpf
specific builtins.

> 
> The following are left out of scope for this effort:
> 
> * 16 and 8 bit operations
> * Explicit memory barriers
> 
> Encoding
> ========
> 
> I originally planned to add new values for bpf_insn.opcode. This was
> rather unpleasant: the opcode space has holes in it but no entire
> instruction classes[2]. Yonghong Song had a better idea: use the
> immediate field of the existing STX XADD instruction to encode the
> operation. This works nicely, without breaking existing programs,
> because the immediate field is currently reserved-must-be-zero, and
> extra-nicely because BPF_ADD happens to be zero.
> 
> Note that this of course makes immediate-source atomic operations
> impossible. It's hard to imagine a measurable speedup from such
> instructions, and if it existed it would certainly not benefit x86,
> which has no support for them.
> 
> The BPF_OP opcode fields are re-used in the immediate, and an
> additional flag BPF_FETCH is used to mark instructions that should
> fetch a pre-modification value from memory.
> 
> So, BPF_XADD is now called BPF_ATOMIC (the old name is kept to avoid
> breaking userspace builds), and where we previously had .imm = 0, we
> now have .imm = BPF_ADD (which is 0).
> 
> Operands
> ========
> 
> Reg-source eBPF instructions only have two operands, while these
> atomic operations have up to four. To avoid needing to encode
> additional operands, then:
> 
> - One of the input registers is re-used as an output register
>    (e.g. atomic_fetch_add both reads from and writes to the source
>    register).
> 
> - Where necessary (i.e. for cmpxchg) , R0 is "hard-coded" as one of
>    the operands.
> 
> This approach also allows the new eBPF instructions to map directly
> to single x86 instructions.
> 
> [1] Previous patchset:
>      https://lore.kernel.org/bpf/20201123173202.1335708-1-jackmanb@google.com/
> 
> [2] Visualisation of eBPF opcode space:
>      https://gist.github.com/bjackman/00fdad2d5dfff601c1918bc29b16e778
> 
> 
> Brendan Jackman (13):
>    bpf: x86: Factor out emission of ModR/M for *(reg + off)
>    bpf: x86: Factor out emission of REX byte
>    bpf: x86: Factor out function to emit NEG
>    bpf: x86: Factor out a lookup table for some ALU opcodes
>    bpf: Rename BPF_XADD and prepare to encode other atomics in .imm
>    bpf: Move BPF_STX reserved field check into BPF_STX verifier code
>    bpf: Add BPF_FETCH field / create atomic_fetch_add instruction
>    bpf: Add instructions for atomic_[cmp]xchg
>    bpf: Pull out a macro for interpreting atomic ALU operations
>    bpf: Add instructions for atomic[64]_[fetch_]sub
>    bpf: Add bitwise atomic instructions
>    bpf: Add tests for new BPF atomic operations
>    bpf: Document new atomic instructions
> 
>   Documentation/networking/filter.rst           |  57 ++-
>   arch/arm/net/bpf_jit_32.c                     |   7 +-
>   arch/arm64/net/bpf_jit_comp.c                 |  16 +-
>   arch/mips/net/ebpf_jit.c                      |  11 +-
>   arch/powerpc/net/bpf_jit_comp64.c             |  25 +-
>   arch/riscv/net/bpf_jit_comp32.c               |  20 +-
>   arch/riscv/net/bpf_jit_comp64.c               |  16 +-
>   arch/s390/net/bpf_jit_comp.c                  |  27 +-
>   arch/sparc/net/bpf_jit_comp_64.c              |  17 +-
>   arch/x86/net/bpf_jit_comp.c                   | 252 ++++++++++----
>   arch/x86/net/bpf_jit_comp32.c                 |   6 +-
>   drivers/net/ethernet/netronome/nfp/bpf/jit.c  |  14 +-
>   drivers/net/ethernet/netronome/nfp/bpf/main.h |   4 +-
>   .../net/ethernet/netronome/nfp/bpf/verifier.c |  15 +-
>   include/linux/filter.h                        | 117 ++++++-
>   include/uapi/linux/bpf.h                      |   8 +-
>   kernel/bpf/core.c                             |  67 +++-
>   kernel/bpf/disasm.c                           |  41 ++-
>   kernel/bpf/verifier.c                         |  77 +++-
>   lib/test_bpf.c                                |   2 +-
>   samples/bpf/bpf_insn.h                        |   4 +-
>   samples/bpf/sock_example.c                    |   2 +-
>   samples/bpf/test_cgrp2_attach.c               |   4 +-
>   tools/include/linux/filter.h                  | 117 ++++++-
>   tools/include/uapi/linux/bpf.h                |   8 +-
>   tools/testing/selftests/bpf/Makefile          |  12 +-
>   .../selftests/bpf/prog_tests/atomics_test.c   | 329 ++++++++++++++++++
>   .../bpf/prog_tests/cgroup_attach_multi.c      |   4 +-
>   .../selftests/bpf/progs/atomics_test.c        | 124 +++++++
>   .../selftests/bpf/verifier/atomic_and.c       |  77 ++++
>   .../selftests/bpf/verifier/atomic_cmpxchg.c   |  96 +++++
>   .../selftests/bpf/verifier/atomic_fetch_add.c | 106 ++++++
>   .../selftests/bpf/verifier/atomic_or.c        |  77 ++++
>   .../selftests/bpf/verifier/atomic_sub.c       |  44 +++
>   .../selftests/bpf/verifier/atomic_xchg.c      |  46 +++
>   .../selftests/bpf/verifier/atomic_xor.c       |  77 ++++
>   tools/testing/selftests/bpf/verifier/ctx.c    |   7 +-
>   .../testing/selftests/bpf/verifier/leak_ptr.c |   4 +-
>   tools/testing/selftests/bpf/verifier/unpriv.c |   3 +-
>   tools/testing/selftests/bpf/verifier/xadd.c   |   2 +-
>   40 files changed, 1754 insertions(+), 188 deletions(-)
>   create mode 100644 tools/testing/selftests/bpf/prog_tests/atomics_test.c
>   create mode 100644 tools/testing/selftests/bpf/progs/atomics_test.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_and.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_fetch_add.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_or.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_sub.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xchg.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xor.c
> 
> --
> 2.29.2.454.gaff20da3a2-goog
> 

Re: [PATCH v2 bpf-next 00/13] Atomics for eBPF

[Alexei Starovoitov]

On Fri, Nov 27, 2020 at 09:53:05PM -0800, Yonghong Song wrote:
> 
> 
> On 11/27/20 9:57 AM, Brendan Jackman wrote:
> > Status of the patches
> > =====================
> > 
> > Thanks for the reviews! Differences from v1->v2 [1]:
> > 
> > * Fixed mistakes in the netronome driver
> > 
> > * Addd sub, add, or, xor operations
> > 
> > * The above led to some refactors to keep things readable. (Maybe I
> >    should have just waited until I'd implemented these before starting
> >    the review...)
> > 
> > * Replaced BPF_[CMP]SET | BPF_FETCH with just BPF_[CMP]XCHG, which
> >    include the BPF_FETCH flag
> > 
> > * Added a bit of documentation. Suggestions welcome for more places
> >    to dump this info...
> > 
> > The prog_test that's added depends on Clang/LLVM features added by
> > Yonghong in https://reviews.llvm.org/D72184
> > 
> > This only includes a JIT implementation for x86_64 - I don't plan to
> > implement JIT support myself for other architectures.
> > 
> > Operations
> > ==========
> > 
> > This patchset adds atomic operations to the eBPF instruction set. The
> > use-case that motivated this work was a trivial and efficient way to
> > generate globally-unique cookies in BPF progs, but I think it's
> > obvious that these features are pretty widely applicable.  The
> > instructions that are added here can be summarised with this list of
> > kernel operations:
> > 
> > * atomic[64]_[fetch_]add
> > * atomic[64]_[fetch_]sub
> > * atomic[64]_[fetch_]and
> > * atomic[64]_[fetch_]or
> 
> * atomic[64]_[fetch_]xor
> 
> > * atomic[64]_xchg
> > * atomic[64]_cmpxchg
> 
> Thanks. Overall looks good to me but I did not check carefully
> on jit part as I am not an expert in x64 assembly...
> 
> This patch also introduced atomic[64]_{sub,and,or,xor}, similar to
> xadd. I am not sure whether it is necessary. For one thing,
> users can just use atomic[64]_fetch_{sub,and,or,xor} to ignore
> return value and they will achieve the same result, right?
> From llvm side, there is no ready-to-use gcc builtin matching
> atomic[64]_{sub,and,or,xor} which does not have return values.
> If we go this route, we will need to invent additional bpf
> specific builtins.

I think bpf specific builtins are overkill.
As you said the users can use atomic_fetch_xor() and ignore
return value. I think llvm backend should be smart enough to use
BPF_ATOMIC | BPF_XOR insn without BPF_FETCH bit in such case.
But if it's too cumbersome to do at the moment we skip this
optimization for now.

Re: [PATCH v2 bpf-next 00/13] Atomics for eBPF

[Yonghong Song]

On 11/28/20 5:40 PM, Alexei Starovoitov wrote:
> On Fri, Nov 27, 2020 at 09:53:05PM -0800, Yonghong Song wrote:
>>
>>
>> On 11/27/20 9:57 AM, Brendan Jackman wrote:
>>> Status of the patches
>>> =====================
>>>
>>> Thanks for the reviews! Differences from v1->v2 [1]:
>>>
>>> * Fixed mistakes in the netronome driver
>>>
>>> * Addd sub, add, or, xor operations
>>>
>>> * The above led to some refactors to keep things readable. (Maybe I
>>>     should have just waited until I'd implemented these before starting
>>>     the review...)
>>>
>>> * Replaced BPF_[CMP]SET | BPF_FETCH with just BPF_[CMP]XCHG, which
>>>     include the BPF_FETCH flag
>>>
>>> * Added a bit of documentation. Suggestions welcome for more places
>>>     to dump this info...
>>>
>>> The prog_test that's added depends on Clang/LLVM features added by
>>> Yonghong in https://reviews.llvm.org/D72184
>>>
>>> This only includes a JIT implementation for x86_64 - I don't plan to
>>> implement JIT support myself for other architectures.
>>>
>>> Operations
>>> ==========
>>>
>>> This patchset adds atomic operations to the eBPF instruction set. The
>>> use-case that motivated this work was a trivial and efficient way to
>>> generate globally-unique cookies in BPF progs, but I think it's
>>> obvious that these features are pretty widely applicable.  The
>>> instructions that are added here can be summarised with this list of
>>> kernel operations:
>>>
>>> * atomic[64]_[fetch_]add
>>> * atomic[64]_[fetch_]sub
>>> * atomic[64]_[fetch_]and
>>> * atomic[64]_[fetch_]or
>>
>> * atomic[64]_[fetch_]xor
>>
>>> * atomic[64]_xchg
>>> * atomic[64]_cmpxchg
>>
>> Thanks. Overall looks good to me but I did not check carefully
>> on jit part as I am not an expert in x64 assembly...
>>
>> This patch also introduced atomic[64]_{sub,and,or,xor}, similar to
>> xadd. I am not sure whether it is necessary. For one thing,
>> users can just use atomic[64]_fetch_{sub,and,or,xor} to ignore
>> return value and they will achieve the same result, right?
>>  From llvm side, there is no ready-to-use gcc builtin matching
>> atomic[64]_{sub,and,or,xor} which does not have return values.
>> If we go this route, we will need to invent additional bpf
>> specific builtins.
> 
> I think bpf specific builtins are overkill.
> As you said the users can use atomic_fetch_xor() and ignore
> return value. I think llvm backend should be smart enough to use
> BPF_ATOMIC | BPF_XOR insn without BPF_FETCH bit in such case.
> But if it's too cumbersome to do at the moment we skip this
> optimization for now.

We can initially all have BPF_FETCH bit as at that point we do not
have def-use chain. Later on we can add a
machine ssa IR phase and check whether the result of, say 
atomic_fetch_or(), is used or not. If not, we can change the
instruction to atomic_or.

> 

Re: [PATCH v2 bpf-next 00/13] Atomics for eBPF

[Yonghong Song]

On 11/30/20 9:22 AM, Yonghong Song wrote:
> 
> 
> On 11/28/20 5:40 PM, Alexei Starovoitov wrote:
>> On Fri, Nov 27, 2020 at 09:53:05PM -0800, Yonghong Song wrote:
>>>
>>>
>>> On 11/27/20 9:57 AM, Brendan Jackman wrote:
>>>> Status of the patches
>>>> =====================
>>>>
>>>> Thanks for the reviews! Differences from v1->v2 [1]:
>>>>
>>>> * Fixed mistakes in the netronome driver
>>>>
>>>> * Addd sub, add, or, xor operations
>>>>
>>>> * The above led to some refactors to keep things readable. (Maybe I
>>>>     should have just waited until I'd implemented these before starting
>>>>     the review...)
>>>>
>>>> * Replaced BPF_[CMP]SET | BPF_FETCH with just BPF_[CMP]XCHG, which
>>>>     include the BPF_FETCH flag
>>>>
>>>> * Added a bit of documentation. Suggestions welcome for more places
>>>>     to dump this info...
>>>>
>>>> The prog_test that's added depends on Clang/LLVM features added by
>>>> Yonghong in 
>>>> https://reviews.llvm.org/D72184 
>>>>
>>>> This only includes a JIT implementation for x86_64 - I don't plan to
>>>> implement JIT support myself for other architectures.
>>>>
>>>> Operations
>>>> ==========
>>>>
>>>> This patchset adds atomic operations to the eBPF instruction set. The
>>>> use-case that motivated this work was a trivial and efficient way to
>>>> generate globally-unique cookies in BPF progs, but I think it's
>>>> obvious that these features are pretty widely applicable.  The
>>>> instructions that are added here can be summarised with this list of
>>>> kernel operations:
>>>>
>>>> * atomic[64]_[fetch_]add
>>>> * atomic[64]_[fetch_]sub
>>>> * atomic[64]_[fetch_]and
>>>> * atomic[64]_[fetch_]or
>>>
>>> * atomic[64]_[fetch_]xor
>>>
>>>> * atomic[64]_xchg
>>>> * atomic[64]_cmpxchg
>>>
>>> Thanks. Overall looks good to me but I did not check carefully
>>> on jit part as I am not an expert in x64 assembly...
>>>
>>> This patch also introduced atomic[64]_{sub,and,or,xor}, similar to
>>> xadd. I am not sure whether it is necessary. For one thing,
>>> users can just use atomic[64]_fetch_{sub,and,or,xor} to ignore
>>> return value and they will achieve the same result, right?
>>>  From llvm side, there is no ready-to-use gcc builtin matching
>>> atomic[64]_{sub,and,or,xor} which does not have return values.
>>> If we go this route, we will need to invent additional bpf
>>> specific builtins.
>>
>> I think bpf specific builtins are overkill.
>> As you said the users can use atomic_fetch_xor() and ignore
>> return value. I think llvm backend should be smart enough to use
>> BPF_ATOMIC | BPF_XOR insn without BPF_FETCH bit in such case.
>> But if it's too cumbersome to do at the moment we skip this
>> optimization for now.
> 
> We can initially all have BPF_FETCH bit as at that point we do not
> have def-use chain. Later on we can add a
> machine ssa IR phase and check whether the result of, say 
> atomic_fetch_or(), is used or not. If not, we can change the
> instruction to atomic_or.

Just implemented what we discussed above in llvm:
   https://reviews.llvm.org/D72184
main change:
   1. atomic_fetch_sub (and later atomic_sub) is gone. llvm will
      transparently transforms it to negation followed by
      atomic_fetch_add or atomic_add (xadd). Kernel can remove
      atomic_fetch_sub/atomic_sub insns.
   2. added new instructions for atomic_{and, or, xor}.
   3. for gcc builtin e.g., __sync_fetch_and_or(), if return
      value is used, atomic_fetch_or will be generated. Otherwise,
      atomic_or will be generated.

Re: [PATCH v2 bpf-next 00/13] Atomics for eBPF

[Andrii Nakryiko]

On Mon, Nov 30, 2020 at 7:51 PM Yonghong Song <yhs@fb.com> wrote:
>
>
>
> On 11/30/20 9:22 AM, Yonghong Song wrote:
> >
> >
> > On 11/28/20 5:40 PM, Alexei Starovoitov wrote:
> >> On Fri, Nov 27, 2020 at 09:53:05PM -0800, Yonghong Song wrote:
> >>>
> >>>
> >>> On 11/27/20 9:57 AM, Brendan Jackman wrote:
> >>>> Status of the patches
> >>>> =====================
> >>>>
> >>>> Thanks for the reviews! Differences from v1->v2 [1]:
> >>>>
> >>>> * Fixed mistakes in the netronome driver
> >>>>
> >>>> * Addd sub, add, or, xor operations
> >>>>
> >>>> * The above led to some refactors to keep things readable. (Maybe I
> >>>>     should have just waited until I'd implemented these before starting
> >>>>     the review...)
> >>>>
> >>>> * Replaced BPF_[CMP]SET | BPF_FETCH with just BPF_[CMP]XCHG, which
> >>>>     include the BPF_FETCH flag
> >>>>
> >>>> * Added a bit of documentation. Suggestions welcome for more places
> >>>>     to dump this info...
> >>>>
> >>>> The prog_test that's added depends on Clang/LLVM features added by
> >>>> Yonghong in
> >>>> https://reviews.llvm.org/D72184
> >>>>
> >>>> This only includes a JIT implementation for x86_64 - I don't plan to
> >>>> implement JIT support myself for other architectures.
> >>>>
> >>>> Operations
> >>>> ==========
> >>>>
> >>>> This patchset adds atomic operations to the eBPF instruction set. The
> >>>> use-case that motivated this work was a trivial and efficient way to
> >>>> generate globally-unique cookies in BPF progs, but I think it's
> >>>> obvious that these features are pretty widely applicable.  The
> >>>> instructions that are added here can be summarised with this list of
> >>>> kernel operations:
> >>>>
> >>>> * atomic[64]_[fetch_]add
> >>>> * atomic[64]_[fetch_]sub
> >>>> * atomic[64]_[fetch_]and
> >>>> * atomic[64]_[fetch_]or
> >>>
> >>> * atomic[64]_[fetch_]xor
> >>>
> >>>> * atomic[64]_xchg
> >>>> * atomic[64]_cmpxchg
> >>>
> >>> Thanks. Overall looks good to me but I did not check carefully
> >>> on jit part as I am not an expert in x64 assembly...
> >>>
> >>> This patch also introduced atomic[64]_{sub,and,or,xor}, similar to
> >>> xadd. I am not sure whether it is necessary. For one thing,
> >>> users can just use atomic[64]_fetch_{sub,and,or,xor} to ignore
> >>> return value and they will achieve the same result, right?
> >>>  From llvm side, there is no ready-to-use gcc builtin matching
> >>> atomic[64]_{sub,and,or,xor} which does not have return values.
> >>> If we go this route, we will need to invent additional bpf
> >>> specific builtins.
> >>
> >> I think bpf specific builtins are overkill.
> >> As you said the users can use atomic_fetch_xor() and ignore
> >> return value. I think llvm backend should be smart enough to use
> >> BPF_ATOMIC | BPF_XOR insn without BPF_FETCH bit in such case.
> >> But if it's too cumbersome to do at the moment we skip this
> >> optimization for now.
> >
> > We can initially all have BPF_FETCH bit as at that point we do not
> > have def-use chain. Later on we can add a
> > machine ssa IR phase and check whether the result of, say
> > atomic_fetch_or(), is used or not. If not, we can change the
> > instruction to atomic_or.
>
> Just implemented what we discussed above in llvm:
>    https://reviews.llvm.org/D72184
> main change:
>    1. atomic_fetch_sub (and later atomic_sub) is gone. llvm will
>       transparently transforms it to negation followed by
>       atomic_fetch_add or atomic_add (xadd). Kernel can remove
>       atomic_fetch_sub/atomic_sub insns.
>    2. added new instructions for atomic_{and, or, xor}.
>    3. for gcc builtin e.g., __sync_fetch_and_or(), if return
>       value is used, atomic_fetch_or will be generated. Otherwise,
>       atomic_or will be generated.

Great, this means that all existing valid uses of
__sync_fetch_and_add() will generate BPF_XADD instructions and will
work on old kernels, right?

If that's the case, do we still need cpu=v4? The new instructions are
*only* going to be generated if the user uses previously unsupported
__sync_fetch_xxx() intrinsics. So, in effect, the user consciously
opts into using new BPF instructions. cpu=v4 seems like an unnecessary
tautology then?

Re: [PATCH v2 bpf-next 00/13] Atomics for eBPF

[Yonghong Song]

On 12/1/20 6:00 PM, Andrii Nakryiko wrote:
> On Mon, Nov 30, 2020 at 7:51 PM Yonghong Song <yhs@fb.com> wrote:
>>
>>
>>
>> On 11/30/20 9:22 AM, Yonghong Song wrote:
>>>
>>>
>>> On 11/28/20 5:40 PM, Alexei Starovoitov wrote:
>>>> On Fri, Nov 27, 2020 at 09:53:05PM -0800, Yonghong Song wrote:
>>>>>
>>>>>
>>>>> On 11/27/20 9:57 AM, Brendan Jackman wrote:
>>>>>> Status of the patches
>>>>>> =====================
>>>>>>
>>>>>> Thanks for the reviews! Differences from v1->v2 [1]:
>>>>>>
>>>>>> * Fixed mistakes in the netronome driver
>>>>>>
>>>>>> * Addd sub, add, or, xor operations
>>>>>>
>>>>>> * The above led to some refactors to keep things readable. (Maybe I
>>>>>>      should have just waited until I'd implemented these before starting
>>>>>>      the review...)
>>>>>>
>>>>>> * Replaced BPF_[CMP]SET | BPF_FETCH with just BPF_[CMP]XCHG, which
>>>>>>      include the BPF_FETCH flag
>>>>>>
>>>>>> * Added a bit of documentation. Suggestions welcome for more places
>>>>>>      to dump this info...
>>>>>>
>>>>>> The prog_test that's added depends on Clang/LLVM features added by
>>>>>> Yonghong in
>>>>>> https://reviews.llvm.org/D72184
>>>>>>
>>>>>> This only includes a JIT implementation for x86_64 - I don't plan to
>>>>>> implement JIT support myself for other architectures.
>>>>>>
>>>>>> Operations
>>>>>> ==========
>>>>>>
>>>>>> This patchset adds atomic operations to the eBPF instruction set. The
>>>>>> use-case that motivated this work was a trivial and efficient way to
>>>>>> generate globally-unique cookies in BPF progs, but I think it's
>>>>>> obvious that these features are pretty widely applicable.  The
>>>>>> instructions that are added here can be summarised with this list of
>>>>>> kernel operations:
>>>>>>
>>>>>> * atomic[64]_[fetch_]add
>>>>>> * atomic[64]_[fetch_]sub
>>>>>> * atomic[64]_[fetch_]and
>>>>>> * atomic[64]_[fetch_]or
>>>>>
>>>>> * atomic[64]_[fetch_]xor
>>>>>
>>>>>> * atomic[64]_xchg
>>>>>> * atomic[64]_cmpxchg
>>>>>
>>>>> Thanks. Overall looks good to me but I did not check carefully
>>>>> on jit part as I am not an expert in x64 assembly...
>>>>>
>>>>> This patch also introduced atomic[64]_{sub,and,or,xor}, similar to
>>>>> xadd. I am not sure whether it is necessary. For one thing,
>>>>> users can just use atomic[64]_fetch_{sub,and,or,xor} to ignore
>>>>> return value and they will achieve the same result, right?
>>>>>   From llvm side, there is no ready-to-use gcc builtin matching
>>>>> atomic[64]_{sub,and,or,xor} which does not have return values.
>>>>> If we go this route, we will need to invent additional bpf
>>>>> specific builtins.
>>>>
>>>> I think bpf specific builtins are overkill.
>>>> As you said the users can use atomic_fetch_xor() and ignore
>>>> return value. I think llvm backend should be smart enough to use
>>>> BPF_ATOMIC | BPF_XOR insn without BPF_FETCH bit in such case.
>>>> But if it's too cumbersome to do at the moment we skip this
>>>> optimization for now.
>>>
>>> We can initially all have BPF_FETCH bit as at that point we do not
>>> have def-use chain. Later on we can add a
>>> machine ssa IR phase and check whether the result of, say
>>> atomic_fetch_or(), is used or not. If not, we can change the
>>> instruction to atomic_or.
>>
>> Just implemented what we discussed above in llvm:
>>     https://reviews.llvm.org/D72184
>> main change:
>>     1. atomic_fetch_sub (and later atomic_sub) is gone. llvm will
>>        transparently transforms it to negation followed by
>>        atomic_fetch_add or atomic_add (xadd). Kernel can remove
>>        atomic_fetch_sub/atomic_sub insns.
>>     2. added new instructions for atomic_{and, or, xor}.
>>     3. for gcc builtin e.g., __sync_fetch_and_or(), if return
>>        value is used, atomic_fetch_or will be generated. Otherwise,
>>        atomic_or will be generated.
> 
> Great, this means that all existing valid uses of
> __sync_fetch_and_add() will generate BPF_XADD instructions and will
> work on old kernels, right?

That is correct.

> 
> If that's the case, do we still need cpu=v4? The new instructions are
> *only* going to be generated if the user uses previously unsupported
> __sync_fetch_xxx() intrinsics. So, in effect, the user consciously
> opts into using new BPF instructions. cpu=v4 seems like an unnecessary
> tautology then?

This is a very good question. Essentially this boils to when users can 
use the new functionality including meaningful return value  of 
__sync_fetch_and_add().
   (1). user can write a small bpf program to test the feature. If user
        gets a failed compilation (fatal error), it won't be supported.
        Otherwise, it is supported.
   (2). compiler provides some way to tell user it is safe to use, e.g.,
        -mcpu=v4, or some clang macro suggested by Brendan earlier.

I guess since kernel already did a lot of feature discovery. Option (1)
is probably fine.

Re: [PATCH v2 bpf-next 00/13] Atomics for eBPF

[John Fastabend]

Yonghong Song wrote:
> 
> 

[...]

> > Great, this means that all existing valid uses of
> > __sync_fetch_and_add() will generate BPF_XADD instructions and will
> > work on old kernels, right?
> 
> That is correct.
> 
> > 
> > If that's the case, do we still need cpu=v4? The new instructions are
> > *only* going to be generated if the user uses previously unsupported
> > __sync_fetch_xxx() intrinsics. So, in effect, the user consciously
> > opts into using new BPF instructions. cpu=v4 seems like an unnecessary
> > tautology then?
> 
> This is a very good question. Essentially this boils to when users can 
> use the new functionality including meaningful return value  of 
> __sync_fetch_and_add().
>    (1). user can write a small bpf program to test the feature. If user
>         gets a failed compilation (fatal error), it won't be supported.
>         Otherwise, it is supported.
>    (2). compiler provides some way to tell user it is safe to use, e.g.,
>         -mcpu=v4, or some clang macro suggested by Brendan earlier.
> 
> I guess since kernel already did a lot of feature discovery. Option (1)
> is probably fine.

For option (2) we can use BTF with kernel version check. If kernel is
greater than kernel this lands in we use the the new instructions if
not we use a slower locked version. That should work for all cases
unless someone backports patches into an older case.

At least thats what I'll probably end up wrapping in a helper function.

Re: [PATCH v2 bpf-next 00/13] Atomics for eBPF

[Andrii Nakryiko]

On Tue, Dec 1, 2020 at 9:53 PM John Fastabend <john.fastabend@gmail.com> wrote:
>
> Yonghong Song wrote:
> >
> >
>
> [...]
>
> > > Great, this means that all existing valid uses of
> > > __sync_fetch_and_add() will generate BPF_XADD instructions and will
> > > work on old kernels, right?
> >
> > That is correct.
> >
> > >
> > > If that's the case, do we still need cpu=v4? The new instructions are
> > > *only* going to be generated if the user uses previously unsupported
> > > __sync_fetch_xxx() intrinsics. So, in effect, the user consciously
> > > opts into using new BPF instructions. cpu=v4 seems like an unnecessary
> > > tautology then?
> >
> > This is a very good question. Essentially this boils to when users can
> > use the new functionality including meaningful return value  of
> > __sync_fetch_and_add().
> >    (1). user can write a small bpf program to test the feature. If user
> >         gets a failed compilation (fatal error), it won't be supported.
> >         Otherwise, it is supported.
> >    (2). compiler provides some way to tell user it is safe to use, e.g.,
> >         -mcpu=v4, or some clang macro suggested by Brendan earlier.
> >
> > I guess since kernel already did a lot of feature discovery. Option (1)
> > is probably fine.
>
> For option (2) we can use BTF with kernel version check. If kernel is
> greater than kernel this lands in we use the the new instructions if
> not we use a slower locked version. That should work for all cases
> unless someone backports patches into an older case.

Two different things: Clang support detection and kernel support
detection. You are talking about kernel detection, I and Yonghong were
talking about Clang detection and explicit cpu=v4 opt-in.

For kernel detection, if there is an enum value or type that gets
added along the feature, then with CO-RE built-ins it's easy to detect
and kernel dead code elimination will make sure that unsupported
instructions won't trip up the BPF verifier. Still need Clang support
to compile the program in the first place, though.

If there is no such BTF-based way to check, it is still possible to
try to load a trivial BPF program with __sync_fech_and_xxx() to do
feature detection and then use .rodata to turn off code paths relying
on a new instruction set.

>
> At least thats what I'll probably end up wrapping in a helper function.

Re: [PATCH v2 bpf-next 00/13] Atomics for eBPF

[John Fastabend]

Andrii Nakryiko wrote:
> On Tue, Dec 1, 2020 at 9:53 PM John Fastabend <john.fastabend@gmail.com> wrote:
> >
> > Yonghong Song wrote:
> > >
> > >
> >
> > [...]
> >
> > > > Great, this means that all existing valid uses of
> > > > __sync_fetch_and_add() will generate BPF_XADD instructions and will
> > > > work on old kernels, right?
> > >
> > > That is correct.
> > >
> > > >
> > > > If that's the case, do we still need cpu=v4? The new instructions are
> > > > *only* going to be generated if the user uses previously unsupported
> > > > __sync_fetch_xxx() intrinsics. So, in effect, the user consciously
> > > > opts into using new BPF instructions. cpu=v4 seems like an unnecessary
> > > > tautology then?
> > >
> > > This is a very good question. Essentially this boils to when users can
> > > use the new functionality including meaningful return value  of
> > > __sync_fetch_and_add().
> > >    (1). user can write a small bpf program to test the feature. If user
> > >         gets a failed compilation (fatal error), it won't be supported.
> > >         Otherwise, it is supported.
> > >    (2). compiler provides some way to tell user it is safe to use, e.g.,
> > >         -mcpu=v4, or some clang macro suggested by Brendan earlier.
> > >
> > > I guess since kernel already did a lot of feature discovery. Option (1)
> > > is probably fine.
> >
> > For option (2) we can use BTF with kernel version check. If kernel is
> > greater than kernel this lands in we use the the new instructions if
> > not we use a slower locked version. That should work for all cases
> > unless someone backports patches into an older case.
> 
> Two different things: Clang support detection and kernel support
> detection. You are talking about kernel detection, I and Yonghong were
> talking about Clang detection and explicit cpu=v4 opt-in.
> 

Ah right, catching up on email and reading the thread backwords I lost
the context thanks!

So, I live in a dev world where I control the build infrastructure so
always know clang/llvm versions and features. What I don't know as
well is where the program I just built might be run. So its a bit
of an odd question from my perspective to ask if my clang supports
feature X. If it doesn't support feature X and I want it we upgrade
clang so that it does support it. I don't think we would ever
write a program to test the assertion. Anyways thanks.

> For kernel detection, if there is an enum value or type that gets
> added along the feature, then with CO-RE built-ins it's easy to detect
> and kernel dead code elimination will make sure that unsupported
> instructions won't trip up the BPF verifier. Still need Clang support
> to compile the program in the first place, though.

+1

> 
> If there is no such BTF-based way to check, it is still possible to
> try to load a trivial BPF program with __sync_fech_and_xxx() to do
> feature detection and then use .rodata to turn off code paths relying
> on a new instruction set.

Right.

> 
> >
> > At least thats what I'll probably end up wrapping in a helper function.

Re: [PATCH v2 bpf-next 00/13] Atomics for eBPF

[Yonghong Song]

On 12/1/20 9:05 PM, Yonghong Song wrote:
> 
> 
> On 12/1/20 6:00 PM, Andrii Nakryiko wrote:
>> On Mon, Nov 30, 2020 at 7:51 PM Yonghong Song <yhs@fb.com> wrote:
>>>
>>>
>>>
>>> On 11/30/20 9:22 AM, Yonghong Song wrote:
>>>>
>>>>
>>>> On 11/28/20 5:40 PM, Alexei Starovoitov wrote:
>>>>> On Fri, Nov 27, 2020 at 09:53:05PM -0800, Yonghong Song wrote:
>>>>>>
>>>>>>
>>>>>> On 11/27/20 9:57 AM, Brendan Jackman wrote:
>>>>>>> Status of the patches
>>>>>>> =====================
>>>>>>>
>>>>>>> Thanks for the reviews! Differences from v1->v2 [1]:
>>>>>>>
>>>>>>> * Fixed mistakes in the netronome driver
>>>>>>>
>>>>>>> * Addd sub, add, or, xor operations
>>>>>>>
>>>>>>> * The above led to some refactors to keep things readable. (Maybe I
>>>>>>>      should have just waited until I'd implemented these before 
>>>>>>> starting
>>>>>>>      the review...)
>>>>>>>
>>>>>>> * Replaced BPF_[CMP]SET | BPF_FETCH with just BPF_[CMP]XCHG, which
>>>>>>>      include the BPF_FETCH flag
>>>>>>>
>>>>>>> * Added a bit of documentation. Suggestions welcome for more places
>>>>>>>      to dump this info...
>>>>>>>
>>>>>>> The prog_test that's added depends on Clang/LLVM features added by
>>>>>>> Yonghong in
>>>>>>> https://reviews.llvm.org/D72184 
>>>>>>>
>>>>>>> This only includes a JIT implementation for x86_64 - I don't plan to
>>>>>>> implement JIT support myself for other architectures.
>>>>>>>
>>>>>>> Operations
>>>>>>> ==========
>>>>>>>
>>>>>>> This patchset adds atomic operations to the eBPF instruction set. 
>>>>>>> The
>>>>>>> use-case that motivated this work was a trivial and efficient way to
>>>>>>> generate globally-unique cookies in BPF progs, but I think it's
>>>>>>> obvious that these features are pretty widely applicable.  The
>>>>>>> instructions that are added here can be summarised with this list of
>>>>>>> kernel operations:
>>>>>>>
>>>>>>> * atomic[64]_[fetch_]add
>>>>>>> * atomic[64]_[fetch_]sub
>>>>>>> * atomic[64]_[fetch_]and
>>>>>>> * atomic[64]_[fetch_]or
>>>>>>
>>>>>> * atomic[64]_[fetch_]xor
>>>>>>
>>>>>>> * atomic[64]_xchg
>>>>>>> * atomic[64]_cmpxchg
>>>>>>
>>>>>> Thanks. Overall looks good to me but I did not check carefully
>>>>>> on jit part as I am not an expert in x64 assembly...
>>>>>>
>>>>>> This patch also introduced atomic[64]_{sub,and,or,xor}, similar to
>>>>>> xadd. I am not sure whether it is necessary. For one thing,
>>>>>> users can just use atomic[64]_fetch_{sub,and,or,xor} to ignore
>>>>>> return value and they will achieve the same result, right?
>>>>>>   From llvm side, there is no ready-to-use gcc builtin matching
>>>>>> atomic[64]_{sub,and,or,xor} which does not have return values.
>>>>>> If we go this route, we will need to invent additional bpf
>>>>>> specific builtins.
>>>>>
>>>>> I think bpf specific builtins are overkill.
>>>>> As you said the users can use atomic_fetch_xor() and ignore
>>>>> return value. I think llvm backend should be smart enough to use
>>>>> BPF_ATOMIC | BPF_XOR insn without BPF_FETCH bit in such case.
>>>>> But if it's too cumbersome to do at the moment we skip this
>>>>> optimization for now.
>>>>
>>>> We can initially all have BPF_FETCH bit as at that point we do not
>>>> have def-use chain. Later on we can add a
>>>> machine ssa IR phase and check whether the result of, say
>>>> atomic_fetch_or(), is used or not. If not, we can change the
>>>> instruction to atomic_or.
>>>
>>> Just implemented what we discussed above in llvm:
>>>     
>>> https://reviews.llvm.org/D72184 
>>> main change:
>>>     1. atomic_fetch_sub (and later atomic_sub) is gone. llvm will
>>>        transparently transforms it to negation followed by
>>>        atomic_fetch_add or atomic_add (xadd). Kernel can remove
>>>        atomic_fetch_sub/atomic_sub insns.
>>>     2. added new instructions for atomic_{and, or, xor}.
>>>     3. for gcc builtin e.g., __sync_fetch_and_or(), if return
>>>        value is used, atomic_fetch_or will be generated. Otherwise,
>>>        atomic_or will be generated.
>>
>> Great, this means that all existing valid uses of
>> __sync_fetch_and_add() will generate BPF_XADD instructions and will
>> work on old kernels, right?
> 
> That is correct.
> 
>>
>> If that's the case, do we still need cpu=v4? The new instructions are
>> *only* going to be generated if the user uses previously unsupported
>> __sync_fetch_xxx() intrinsics. So, in effect, the user consciously
>> opts into using new BPF instructions. cpu=v4 seems like an unnecessary
>> tautology then?
> 
> This is a very good question. Essentially this boils to when users can 
> use the new functionality including meaningful return value  of 
> __sync_fetch_and_add().
>    (1). user can write a small bpf program to test the feature. If user
>         gets a failed compilation (fatal error), it won't be supported.
>         Otherwise, it is supported.
>    (2). compiler provides some way to tell user it is safe to use, e.g.,
>         -mcpu=v4, or some clang macro suggested by Brendan earlier.
> 
> I guess since kernel already did a lot of feature discovery. Option (1)
> is probably fine.

Just pushed a new llvm version (https://reviews.llvm.org/D72184) which
removed -mcpu=v4. The new instructions will be generated by default
for 64bit type. For 32bit type, alu32 is required. Currently -mcpu=v3
already has alu32 as default and kernel supporting atomic insns should
have good alu32 support too. So I decided to have skip non-alu32 32bit
mode. But if people feel strongly to support non-alu32 32bit mode atomic
instructions, I can add them in llvm... The instruction encodings are
the same for alu32/non-alu32 32bit mode so the kernel will not be
impacted.