linux-kernel - Re: [PATCH v2 0/6] arm64/signal: Signal handling cleanups

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Message-ID: <Y9kO1egKjKNqE0zg@arm.com>
Date:   Tue, 31 Jan 2023 12:51:33 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/6] arm64/signal: Signal handling cleanups

Hi Mark,

On Tue, Jan 03, 2023 at 08:25:15PM +0000, Mark Brown wrote:
> This series collects a number of small cleanups to the signal handling
> code which removes redundant validation of size information and avoids
> reading the same data from userspace twice.
> 
> There are some overlaps with both the TPIDR2 signal handling and SME2
> serieses which are also in flight, applying this will require
> adjustments in those serieses and vice versa.
[...]
> Mark Brown (6):
>       arm64/signal: Don't redundantly verify FPSIMD magic
>       arm64/signal: Remove redundant size validation from parse_user_sigframe()
>       arm64/signal: Make interface for restore_fpsimd_context() consistent

I'm fine with the first three patches, they seem correct and make the
frame checking more consistent.

>       arm64/signal: Avoid rereading context frame sizes
>       arm64/signal: Only read new data when parsing the SVE context
>       arm64/signal: Only read new data when parsing the ZA context

I'm not sure these add much to the code readability (and the performance
improvement I guess is negligible). We avoid some copy_from_user() into
the context structures but rely on data read previously or some
get_user() into local variables. Personally I'd make the
restore_fpsimd_context() also do a copy_from_user() for consistency with
the current sve and za frames restoring.

Personal preference, not sure whether Will has the same view.

-- 
Catalin