[PATCH v2 0/2] MIPS: Implement two workarounds for BPF JIT

[PATCH v2 0/2] MIPS: Implement two workarounds for BPF JIT

[Jiaxun Yang]

Hi all,

Just noticed eBPF JIT is not working on R4000 when messing around with QEMU.

This patchset implements two workarounds that is blocking us from enabling eBPF
JIT on R4000.

Thanks.
- Jiaxun

Jiaxun Yang (2):
  MIPS: ebpf jit: Implement DADDI workarounds
  MIPS: ebpf jit: Implement R4000 workarounds

 arch/mips/Kconfig              | 5 +----
 arch/mips/net/bpf_jit_comp.c   | 4 ++++
 arch/mips/net/bpf_jit_comp64.c | 3 +++
 3 files changed, 8 insertions(+), 4 deletions(-)

-- 
2.37.1 (Apple Git-137.1)

[PATCH v2 1/2] MIPS: ebpf jit: Implement DADDI workarounds

[Jiaxun Yang]

For DADDI errata we just workaround by disable immediate operation
for BPF_ADD / BPF_SUB to avoid generation of DADDIU.

All other use cases in JIT won't cause overflow thus they are all safe.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
v2: Drop 64BIT ifdef
---
 arch/mips/Kconfig            | 1 -
 arch/mips/net/bpf_jit_comp.c | 4 ++++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 37072e15b263..df0910e3895c 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -64,7 +64,6 @@ config MIPS
 	select HAVE_DMA_CONTIGUOUS
 	select HAVE_DYNAMIC_FTRACE
 	select HAVE_EBPF_JIT if !CPU_MICROMIPS && \
-				!CPU_DADDI_WORKAROUNDS && \
 				!CPU_R4000_WORKAROUNDS && \
 				!CPU_R4400_WORKAROUNDS
 	select HAVE_EXIT_THREAD
diff --git a/arch/mips/net/bpf_jit_comp.c b/arch/mips/net/bpf_jit_comp.c
index b17130d510d4..a40d926b6513 100644
--- a/arch/mips/net/bpf_jit_comp.c
+++ b/arch/mips/net/bpf_jit_comp.c
@@ -218,9 +218,13 @@ bool valid_alu_i(u8 op, s32 imm)
 		/* All legal eBPF values are valid */
 		return true;
 	case BPF_ADD:
+		if (IS_ENABLED(CONFIG_CPU_DADDI_WORKAROUNDS))
+			return false;
 		/* imm must be 16 bits */
 		return imm >= -0x8000 && imm <= 0x7fff;
 	case BPF_SUB:
+		if (IS_ENABLED(CONFIG_CPU_DADDI_WORKAROUNDS))
+			return false;
 		/* -imm must be 16 bits */
 		return imm >= -0x7fff && imm <= 0x8000;
 	case BPF_AND:
-- 
2.37.1 (Apple Git-137.1)

[PATCH v2 2/2] MIPS: ebpf jit: Implement R4000 workarounds

[Jiaxun Yang]

For R4000 erratas around multiplication and division instructions,
as our use of those instructions are always followed by mflo/mfhi
instructions, the only issue we need care is

"MIPS R4000PC/SC Errata, Processor Revision 2.2 and 3.0" Errata 28:
"A double-word or a variable shift may give an incorrect result if
executed while an integer multiplication is in progress."

We just emit a mfhi $0 to ensure the operation is completed after
every multiplication instruction according to workaround suggestion
in the document.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
---
v2: Drop 32bit part
---
 arch/mips/Kconfig              | 4 +---
 arch/mips/net/bpf_jit_comp64.c | 3 +++
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index df0910e3895c..5ea07c833c5b 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -63,9 +63,7 @@ config MIPS
 	select HAVE_DEBUG_STACKOVERFLOW
 	select HAVE_DMA_CONTIGUOUS
 	select HAVE_DYNAMIC_FTRACE
-	select HAVE_EBPF_JIT if !CPU_MICROMIPS && \
-				!CPU_R4000_WORKAROUNDS && \
-				!CPU_R4400_WORKAROUNDS
+	select HAVE_EBPF_JIT if !CPU_MICROMIPS
 	select HAVE_EXIT_THREAD
 	select HAVE_FAST_GUP
 	select HAVE_FTRACE_MCOUNT_RECORD
diff --git a/arch/mips/net/bpf_jit_comp64.c b/arch/mips/net/bpf_jit_comp64.c
index 0e7c1bdcf914..fa7e9aa37f49 100644
--- a/arch/mips/net/bpf_jit_comp64.c
+++ b/arch/mips/net/bpf_jit_comp64.c
@@ -228,6 +228,9 @@ static void emit_alu_r64(struct jit_context *ctx, u8 dst, u8 src, u8 op)
 		} else {
 			emit(ctx, dmultu, dst, src);
 			emit(ctx, mflo, dst);
+			/* Ensure multiplication is completed */
+			if (IS_ENABLED(CONFIG_CPU_R4000_WORKAROUNDS))
+				emit(ctx, mfhi, MIPS_R_ZERO);
 		}
 		break;
 	/* dst = dst / src */
-- 
2.37.1 (Apple Git-137.1)

Re: [PATCH v2 1/2] MIPS: ebpf jit: Implement DADDI workarounds

[Philippe Mathieu-Daudé]

On 28/2/23 12:33, Jiaxun Yang wrote:
> For DADDI errata we just workaround by disable immediate operation
> for BPF_ADD / BPF_SUB to avoid generation of DADDIU.
> 
> All other use cases in JIT won't cause overflow thus they are all safe.
> 
> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
> ---
> v2: Drop 64BIT ifdef
> ---
>   arch/mips/Kconfig            | 1 -
>   arch/mips/net/bpf_jit_comp.c | 4 ++++
>   2 files changed, 4 insertions(+), 1 deletion(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

Re: [PATCH v2 1/2] MIPS: ebpf jit: Implement DADDI workarounds

[Johan Almbladh]

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

On Tue, Feb 28, 2023 at 12:33 PM Jiaxun Yang <jiaxun.yang@flygoat.com> wrote:
>
> For DADDI errata we just workaround by disable immediate operation
> for BPF_ADD / BPF_SUB to avoid generation of DADDIU.
>
> All other use cases in JIT won't cause overflow thus they are all safe.
>
> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
> ---
> v2: Drop 64BIT ifdef
> ---
>  arch/mips/Kconfig            | 1 -
>  arch/mips/net/bpf_jit_comp.c | 4 ++++
>  2 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 37072e15b263..df0910e3895c 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -64,7 +64,6 @@ config MIPS
>         select HAVE_DMA_CONTIGUOUS
>         select HAVE_DYNAMIC_FTRACE
>         select HAVE_EBPF_JIT if !CPU_MICROMIPS && \
> -                               !CPU_DADDI_WORKAROUNDS && \
>                                 !CPU_R4000_WORKAROUNDS && \
>                                 !CPU_R4400_WORKAROUNDS
>         select HAVE_EXIT_THREAD
> diff --git a/arch/mips/net/bpf_jit_comp.c b/arch/mips/net/bpf_jit_comp.c
> index b17130d510d4..a40d926b6513 100644
> --- a/arch/mips/net/bpf_jit_comp.c
> +++ b/arch/mips/net/bpf_jit_comp.c
> @@ -218,9 +218,13 @@ bool valid_alu_i(u8 op, s32 imm)
>                 /* All legal eBPF values are valid */
>                 return true;
>         case BPF_ADD:
> +               if (IS_ENABLED(CONFIG_CPU_DADDI_WORKAROUNDS))
> +                       return false;
>                 /* imm must be 16 bits */
>                 return imm >= -0x8000 && imm <= 0x7fff;
>         case BPF_SUB:
> +               if (IS_ENABLED(CONFIG_CPU_DADDI_WORKAROUNDS))
> +                       return false;
>                 /* -imm must be 16 bits */
>                 return imm >= -0x7fff && imm <= 0x8000;
>         case BPF_AND:
> --
> 2.37.1 (Apple Git-137.1)
>

Re: [PATCH v2 0/2] MIPS: Implement two workarounds for BPF JIT

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Tue, 28 Feb 2023 11:33:03 +0000 you wrote:
> Hi all,
> 
> Just noticed eBPF JIT is not working on R4000 when messing around with QEMU.
> 
> This patchset implements two workarounds that is blocking us from enabling eBPF
> JIT on R4000.
> 
> [...]

Here is the summary with links:
  - [v2,1/2] MIPS: ebpf jit: Implement DADDI workarounds
    https://git.kernel.org/bpf/bpf-next/c/bbefef2f0708
  - [v2,2/2] MIPS: ebpf jit: Implement R4000 workarounds
    https://git.kernel.org/bpf/bpf-next/c/7364d60c2661

You are awesome, thank you!
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