linux-kernel - Re: [PATCH v2] arm64: fix bug for reloading FPSIMD state after cpu power off

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Message-ID: <20140901093427.GC608@arm.com>
Date:	Mon, 1 Sep 2014 10:34:28 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Leo Yan <leoy@...vell.com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ard.biesheuvel@...aro.org" <ard.biesheuvel@...aro.org>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v2] arm64: fix bug for reloading FPSIMD state after cpu
 power off

On Mon, Sep 01, 2014 at 04:09:51AM +0100, Leo Yan wrote:
> Now arm64 defers reloading FPSIMD state, but this optimization also
> introduces the bug after cpu resume back from low power mode.
> 
> The reason is after the cpu has been powered off, s/w need set the
> cpu's fpsimd_last_state to NULL so that it will force to reload
> FPSIMD state for the thread, otherwise there has the chance to meet
> the condition for both the task's fpsimd_state.cpu field contains the
> id of the current cpu, and the cpu's fpsimd_last_state per-cpu variable
> points to the task's fpsimd_state, so finally kernel will skip to reload
> the context during it return back to userland.
> 
> Signed-off-by: Leo Yan <leoy@...vell.com>

Reviewed-by: Catalin Marinas <catalin.marinas@....com>

(and cc'ing Will to pick it up since he's handling the 3.17 release)

Thanks.
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