linux-kernel - Re: [PATCH] arm64/sme: Clearing TIF_SVE but not TIF_SME in za

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Message-ID: <YwS5cN7GlbdR5IQU@sirena.org.uk>
Date:   Tue, 23 Aug 2022 12:26:40 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Wang ShaoBo <bobo.shaobowang@...wei.com>
Cc:     catalin.marinas@....com, weiyongjun1@...wei.com,
        guohanjun@...wei.com, oleg@...hat.com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/sme: Clearing TIF_SVE but not TIF_SME in za_set()

On Tue, Aug 23, 2022 at 09:56:27AM +0800, Wang ShaoBo wrote:

> Clearing target's TIF_SVE but not current's TIF_SME in za_set(), as it indicates
> target's SVE storage unavailable.

> +++ b/arch/arm64/kernel/ptrace.c
> @@ -1084,7 +1084,7 @@ static int za_set(struct task_struct *target,
>  	if (!target->thread.sve_state) {
>  		sve_alloc(target);
>  		if (!target->thread.sve_state) {
> -			clear_thread_flag(TIF_SME);
> +			clear_tsk_thread_flag(target, TIF_SVE);
>  			ret = -ENOMEM;
>  			goto out;
>  		}

We didn't set TIF_SVE so we have no reason to clear it here, we know it
can't have been set since there was no sve_state allocated.  The clear
of TIF_SME is happening on the wrong task though, and TBH is just
redudnant for similar reasons.

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