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bpf, mips: Implement R4000 workarounds for JIT

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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>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Link: https://lore.kernel.org/bpf/20230228113305.83751-3-jiaxun.yang@flygoat.com
This commit is contained in:
Jiaxun Yang 2023-02-28 11:33:05 +00:00 committed by Daniel Borkmann
parent bbefef2f07
commit 7364d60c26
2 changed files with 4 additions and 3 deletions
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4
arch/mips/Kconfig
View File

@ -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

3
arch/mips/net/bpf_jit_comp64.c
View File

@ -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 */