linux-kernel - Re: [PATCH] arm64: fix bug for reloading FPSIMD state after CPU hotplug.

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Message-ID: <20150611160856.GC29305@e104818-lin.cambridge.arm.com>
Date:	Thu, 11 Jun 2015 17:08:56 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Chunyan Zhang <chunyan.zhang@...eadtrum.com>
Cc:	will.deacon@....com, janet.liu@...eadtrum.com,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	xiongshan.an@...eadtrum.com
Subject: Re: [PATCH] arm64: fix bug for reloading FPSIMD state after CPU
 hotplug.

On Thu, Jun 11, 2015 at 12:02:45PM +0800, Chunyan Zhang wrote:
> From: Janet Liu <janet.liu@...eadtrum.com>
> 
> Now FPSIMD don't handle HOTPLUG_CPU. This introduces bug after cpu down/up process.
> 
> After cpu down/up process, the FPSMID hardware register is default value, not any
> process's fpsimd context. when CPU_DEAD set cpu's fpsimd_state to NULL, it will force
> to load the fpsimd context for the thread, to avoid the chance to skip to load the context.
> If process A is the last user process on CPU N before cpu down, and the first user process
> on the same CPU N after cpu up, A's fpsimd_state.cpu is the current cpu id,
> and per_cpu(fpsimd_last_state) points A's fpsimd_state, so kernel will not reload the
> context during it return to user space.
> 
> Signed-off-by: Janet Liu <janet.liu@...eadtrum.com>
> Signed-off-by: Xiongshan An <xiongshan.an@...eadtrum.com>
> Signed-off-by: Chunyan Zhang <chunyan.zhang@...eadtrum.com>

Applied. Thanks.

-- 
Catalin
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