linux-kernel - Re: [PATCH 2/2] MIPS: ebpf jit: Implement R4000 workarounds

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Message-ID: <8529a744-721e-218d-7a4c-cbb523a1fc1d@linaro.org>
Date:   Sun, 26 Feb 2023 23:09:40 +0100
From:   Philippe Mathieu-Daudé <philmd@...aro.org>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>, linux-mips@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, tsbogend@...ha.franken.de,
        johan.almbladh@...finetworks.com, paulburton@...nel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH 2/2] MIPS: ebpf jit: Implement R4000 workarounds

On 22/2/23 17:12, Jiaxun Yang 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

Typo "according"

> in the document.
> 
> Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
> ---
>   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(-)

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