linux-kernel - Re: [PATCH v2] riscv: Discard vector state on syscalls

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Message-ID: <87sfaem76q.fsf@all.your.base.are.belong.to.us>
Date:   Mon, 26 Jun 2023 20:04:13 +0200
From:   Björn Töpel <bjorn@...nel.org>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org
Cc:     Björn Töpel <bjorn@...osinc.com>,
        linux-kernel@...r.kernel.org, linux@...osinc.com,
        Palmer Dabbelt <palmer@...osinc.com>,
        Rémi Denis-Courmont 
        <remi@...lab.net>, Darius Rad <darius@...espec.com>,
        Andy Chiu <andy.chiu@...ive.com>
Subject: Re: [PATCH v2] riscv: Discard vector state on syscalls

Björn Töpel <bjorn@...nel.org> writes:

> Björn Töpel <bjorn@...nel.org> writes:
>
>> From: Björn Töpel <bjorn@...osinc.com>
>>
>> The RISC-V vector specification states:
>>   Executing a system call causes all caller-saved vector registers
>>   (v0-v31, vl, vtype) and vstart to become unspecified.
>
> A bit of a corner case, but this will make sigreturn syscalls discard
> the vector state as well.
>
> Is that an issue? E.g. a user cannot build userspace context switching
> application. Does arm64 SVE handle sigreturn in a special way?

NVM; My bad. The vector state is cleared on *entry*, but then the
registers passed on signal stack is restored as usual.

Sorry for the noise! We're all good!
Björn