linux-kernel - Re: [PATCH v5 3/3] arm64/fpsimd: Don't disable softirq when touching FPSIMD/SVE state

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Date:   Mon, 3 Jun 2019 17:25:34 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Julien Grall <julien.grall@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, will.deacon@....com,
        christoffer.dall@....com, marc.zyngier@....com,
        james.morse@....com, julien.thierry@....com,
        suzuki.poulose@....com, Dave.Martin@....com,
        ard.biesheuvel@...aro.org
Subject: Re: [PATCH v5 3/3] arm64/fpsimd: Don't disable softirq when touching
 FPSIMD/SVE state

On Tue, May 21, 2019 at 06:21:39PM +0100, Julien Grall wrote:
> Since a softirq is supposed to check may_use_simd() anyway before
> attempting to use FPSIMD/SVE, there is limited reason to keep softirq
> disabled when touching the FPSIMD/SVE context. Instead, we can simply
> disable preemption and mark the FPSIMD/SVE context as in use by setting
> CPU's fpsimd_context_busy flag.
[...]
> +static void get_cpu_fpsimd_context(void)
> +{
> +	preempt_disable();
> +	__get_cpu_fpsimd_context();
> +}

Is there anything that prevents a softirq being invoked between
preempt_disable() and __get_cpu_fpsimd_context()?

-- 
Catalin