Commit 7364d60c authored by Jiaxun Yang's avatar Jiaxun Yang Committed by Daniel Borkmann
Browse files

bpf, mips: Implement R4000 workarounds for JIT 



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: default avatarJiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarPhilippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: default avatarJohan Almbladh <johan.almbladh@anyfinetworks.com>
Link: https://lore.kernel.org/bpf/20230228113305.83751-3-jiaxun.yang@flygoat.com
parent bbefef2f

arch/mips/Kconfig

+1 −3
Original line number Diff line number Diff line
@@ -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

arch/mips/net/bpf_jit_comp64.c

+3 −0
Original line number Diff line number Diff line
@@ -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 */