> 2023年2月23日 10:22，Johan Almbladh <johan.almbladh@xxxxxxxxxxxxxxxxx> 写道：
>
> On Wed, Feb 22, 2023 at 5:12 PM Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx> wrote:
>>
>> 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 $0 to ensure the operation is completed after
>> every multiplication instruction accorading to workaround suggestion
>> in the document.
>>
>> Signed-off-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>
>> ---
>> arch/mips/Kconfig | 4 +---
>> arch/mips/net/bpf_jit_comp32.c | 4 ++++
>> arch/mips/net/bpf_jit_comp64.c | 3 +++
>> 3 files changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
>> index df0910e3895c..5ea07c833c5b 100644
>> --- a/arch/mips/Kconfig
>> +++ b/arch/mips/Kconfig
>> @@ -63,9 +63,7 @@ config MIPS
>> select HAVE_DEBUG_STACKOVERFLOW
>> select HAVE_DMA_CONTIGUOUS
>> select HAVE_DYNAMIC_FTRACE
>> - select HAVE_EBPF_JIT if !CPU_MICROMIPS && \
>> - !CPU_R4000_WORKAROUNDS && \
>> - !CPU_R4400_WORKAROUNDS
>
> Is the R4400 errata also covered by this workaround?
Yes, R4400 errata is basically a reduced version of R4000 one.
They managed to fix some parts of the issue but not all.
>
>> + select HAVE_EBPF_JIT if !CPU_MICROMIPS
>> select HAVE_EXIT_THREAD
>> select HAVE_FAST_GUP
>> select HAVE_FTRACE_MCOUNT_RECORD
>> diff --git a/arch/mips/net/bpf_jit_comp32.c b/arch/mips/net/bpf_jit_comp32.c
>> index ace5db3fbd17..fee334544d2f 100644
>> --- a/arch/mips/net/bpf_jit_comp32.c
>> +++ b/arch/mips/net/bpf_jit_comp32.c
>> @@ -446,6 +446,9 @@ static void emit_mul_i64(struct jit_context *ctx, const u8 dst[], s32 imm)
>> } else {
>> emit(ctx, multu, hi(dst), src);
>> emit(ctx, mflo, hi(dst));
>> + /* Ensure multiplication is completed */
>> + if (IS_ENABLED(CONFIG_CPU_R4000_WORKAROUNDS))
>> + emit(ctx, mfhi, MIPS_R_ZERO);
>> }
>>
>> /* hi(dst) = hi(dst) - lo(dst) */
>> @@ -504,6 +507,7 @@ static void emit_mul_r64(struct jit_context *ctx,
>> } else {
>> emit(ctx, multu, lo(dst), lo(src));
>> emit(ctx, mflo, lo(dst));
>> + /* No need for workaround because we have this mfhi */
>> emit(ctx, mfhi, tmp);
>> }
>
> R4000 is a 64-bit CPU, so the 32-bit JIT implementation will not be
> used. From the Makefile:
>
> ifeq ($(CONFIG_32BIT),y)
> obj-$(CONFIG_BPF_JIT) += bpf_jit_comp32.o
> else
> obj-$(CONFIG_BPF_JIT) += bpf_jit_comp64.o
> endif
It’s common practice to run 32-bit kernel on R4000 based systems to save some memory :-)
Thanks.
- Jiaxun
>
>>
>> diff --git a/arch/mips/net/bpf_jit_comp64.c b/arch/mips/net/bpf_jit_comp64.c
>> index 0e7c1bdcf914..5f5a93f997bc 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)
