[PATCH bpf-next 0/2] bpf, mips: Do some small changes

[PATCH bpf-next 0/2] bpf, mips: Do some small changes

[Tiezhu Yang]

This patchset is based on bpf-next tree:
https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git

Tiezhu Yang (2):
  bpf, mips: Clean up config options about JIT
  bpf, mips: Modify check condition about tail call count

 arch/mips/Kconfig              | 9 ---------
 arch/mips/net/Makefile         | 6 +++---
 arch/mips/net/bpf_jit_comp32.c | 4 ++--
 3 files changed, 5 insertions(+), 14 deletions(-)

-- 
2.1.0

[PATCH bpf-next 1/2] bpf, mips: Clean up config options about JIT

[Tiezhu Yang]

The config options MIPS_CBPF_JIT and MIPS_EBPF_JIT are useless, remove
them in arch/mips/Kconfig, and then modify arch/mips/net/Makefile.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 arch/mips/Kconfig      | 9 ---------
 arch/mips/net/Makefile | 6 +++---
 2 files changed, 3 insertions(+), 12 deletions(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 38468f4..9b03c78 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -1214,15 +1214,6 @@ config SYS_SUPPORTS_RELOCATABLE
 	  The platform must provide plat_get_fdt() if it selects CONFIG_USE_OF
 	  to allow access to command line and entropy sources.
 
-config MIPS_CBPF_JIT
-	def_bool y
-	depends on BPF_JIT && HAVE_CBPF_JIT
-
-config MIPS_EBPF_JIT
-	def_bool y
-	depends on BPF_JIT && HAVE_EBPF_JIT
-
-
 #
 # Endianness selection.  Sufficiently obscure so many users don't know what to
 # answer,so we try hard to limit the available choices.  Also the use of a
diff --git a/arch/mips/net/Makefile b/arch/mips/net/Makefile
index 95e8267..e3e6ae6 100644
--- a/arch/mips/net/Makefile
+++ b/arch/mips/net/Makefile
@@ -1,10 +1,10 @@
 # SPDX-License-Identifier: GPL-2.0-only
 # MIPS networking code
 
-obj-$(CONFIG_MIPS_EBPF_JIT) += bpf_jit_comp.o
+obj-$(CONFIG_BPF_JIT) += bpf_jit_comp.o
 
 ifeq ($(CONFIG_32BIT),y)
-        obj-$(CONFIG_MIPS_EBPF_JIT) += bpf_jit_comp32.o
+        obj-$(CONFIG_BPF_JIT) += bpf_jit_comp32.o
 else
-        obj-$(CONFIG_MIPS_EBPF_JIT) += bpf_jit_comp64.o
+        obj-$(CONFIG_BPF_JIT) += bpf_jit_comp64.o
 endif
-- 
2.1.0

[PATCH bpf-next 2/2] bpf, mips: Modify check condition about tail call count

[Tiezhu Yang]

In emit_tail_call() of bpf_jit_comp32.c, "blez t2" (t2 <= 0) is not
consistent with the comment "t2 < 0", modify the check condition to
keep consistency.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 arch/mips/net/bpf_jit_comp32.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mips/net/bpf_jit_comp32.c b/arch/mips/net/bpf_jit_comp32.c
index 9d7041a..b887c01 100644
--- a/arch/mips/net/bpf_jit_comp32.c
+++ b/arch/mips/net/bpf_jit_comp32.c
@@ -1312,12 +1312,12 @@ static int emit_tail_call(struct jit_context *ctx)
 	emit(ctx, sltu, t1, ind, t1);            /* t1 = ind < t1            */
 	emit(ctx, beqz, t1, get_offset(ctx, 1)); /* PC += off(1) if t1 == 0  */
 						 /* (next insn delay slot)   */
-	/* if (TCC-- <= 0) goto out */
+	/* if (--TCC < 0) goto out */
 	emit(ctx, lw, t2, ctx->stack_size, MIPS_R_SP);  /* t2 = *(SP + size) */
 	emit_load_delay(ctx);                     /* Load delay slot         */
-	emit(ctx, blez, t2, get_offset(ctx, 1));  /* PC += off(1) if t2 < 0  */
 	emit(ctx, addiu, t2, t2, -1);             /* t2-- (delay slot)       */
 	emit(ctx, sw, t2, ctx->stack_size, MIPS_R_SP);  /* *(SP + size) = t2 */
+	emit(ctx, bltz, t2, get_offset(ctx, 1));  /* PC += off(1) if t2 < 0  */
 
 	/* prog = ary->ptrs[ind] */
 	off = offsetof(struct bpf_array, ptrs);
-- 
2.1.0

Re: [PATCH bpf-next 2/2] bpf, mips: Modify check condition about tail call count

[Johan Almbladh]

On Sat, Oct 9, 2021 at 12:58 PM Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
>
> In emit_tail_call() of bpf_jit_comp32.c, "blez t2" (t2 <= 0) is not
> consistent with the comment "t2 < 0", modify the check condition to
> keep consistency.
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> ---
>  arch/mips/net/bpf_jit_comp32.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/mips/net/bpf_jit_comp32.c b/arch/mips/net/bpf_jit_comp32.c
> index 9d7041a..b887c01 100644
> --- a/arch/mips/net/bpf_jit_comp32.c
> +++ b/arch/mips/net/bpf_jit_comp32.c
> @@ -1312,12 +1312,12 @@ static int emit_tail_call(struct jit_context *ctx)
>         emit(ctx, sltu, t1, ind, t1);            /* t1 = ind < t1            */
>         emit(ctx, beqz, t1, get_offset(ctx, 1)); /* PC += off(1) if t1 == 0  */
>                                                  /* (next insn delay slot)   */
> -       /* if (TCC-- <= 0) goto out */
> +       /* if (--TCC < 0) goto out */
>         emit(ctx, lw, t2, ctx->stack_size, MIPS_R_SP);  /* t2 = *(SP + size) */
>         emit_load_delay(ctx);                     /* Load delay slot         */
> -       emit(ctx, blez, t2, get_offset(ctx, 1));  /* PC += off(1) if t2 < 0  */
>         emit(ctx, addiu, t2, t2, -1);             /* t2-- (delay slot)       */
>         emit(ctx, sw, t2, ctx->stack_size, MIPS_R_SP);  /* *(SP + size) = t2 */
> +       emit(ctx, bltz, t2, get_offset(ctx, 1));  /* PC += off(1) if t2 < 0  */

If the comment is not consistent with the code, and the code is
correct, why did you change the code? Have you seen the JIT fail on
any of the tail call test cases?

The current code works as intended. The t2 register is decremented in
the branch delay slot of the blez. After your change, the the comment
still says "delay slot", but it is no longer in the delay slot of a
branch. Instead the next instruction emitted, not visible in the patch
context, fills the delay slot of the bltz. In this case it probably is
ok, but if that instruction is also a branch, the result would be
unpredictable.

I prefer to emit the delay slot instruction immediately after the
branch is emitted when possible. If a branch and its delay slot is
separated in the JIT logic, it makes the JIT more brittle IMO.

Please keep the original logic, but update the blez comment so it is
consistent with the code.



>
>         /* prog = ary->ptrs[ind] */
>         off = offsetof(struct bpf_array, ptrs);
> --
> 2.1.0
>

Re: [PATCH bpf-next 1/2] bpf, mips: Clean up config options about JIT

[Johan Almbladh]

On Sat, Oct 9, 2021 at 12:58 PM Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
>
> The config options MIPS_CBPF_JIT and MIPS_EBPF_JIT are useless, remove
> them in arch/mips/Kconfig, and then modify arch/mips/net/Makefile.
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> ---
>  arch/mips/Kconfig      | 9 ---------
>  arch/mips/net/Makefile | 6 +++---
>  2 files changed, 3 insertions(+), 12 deletions(-)
>
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 38468f4..9b03c78 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -1214,15 +1214,6 @@ config SYS_SUPPORTS_RELOCATABLE
>           The platform must provide plat_get_fdt() if it selects CONFIG_USE_OF
>           to allow access to command line and entropy sources.
>
> -config MIPS_CBPF_JIT
> -       def_bool y
> -       depends on BPF_JIT && HAVE_CBPF_JIT
> -
> -config MIPS_EBPF_JIT
> -       def_bool y
> -       depends on BPF_JIT && HAVE_EBPF_JIT
> -
> -
>  #
>  # Endianness selection.  Sufficiently obscure so many users don't know what to
>  # answer,so we try hard to limit the available choices.  Also the use of a
> diff --git a/arch/mips/net/Makefile b/arch/mips/net/Makefile
> index 95e8267..e3e6ae6 100644
> --- a/arch/mips/net/Makefile
> +++ b/arch/mips/net/Makefile
> @@ -1,10 +1,10 @@
>  # SPDX-License-Identifier: GPL-2.0-only
>  # MIPS networking code
>
> -obj-$(CONFIG_MIPS_EBPF_JIT) += bpf_jit_comp.o
> +obj-$(CONFIG_BPF_JIT) += bpf_jit_comp.o
>
>  ifeq ($(CONFIG_32BIT),y)
> -        obj-$(CONFIG_MIPS_EBPF_JIT) += bpf_jit_comp32.o
> +        obj-$(CONFIG_BPF_JIT) += bpf_jit_comp32.o
>  else
> -        obj-$(CONFIG_MIPS_EBPF_JIT) += bpf_jit_comp64.o
> +        obj-$(CONFIG_BPF_JIT) += bpf_jit_comp64.o
>  endif
> --
> 2.1.0
>

Looks good to me.

Acked-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>