linux-kernel - Re: [PATCH] x86, fpu: avoid FPU lazy restore after suspend

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Date:	Fri, 30 Nov 2012 10:57:05 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Vincent Palatin <vpalatin@...omium.org>
CC:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jarkko Sakkinen <jarkko.sakkinen@...el.com>,
	Duncan Laurie <dlaurie@...omium.org>,
	Olof Johansson <olofj@...omium.org>
Subject: Re: [PATCH] x86, fpu: avoid FPU lazy restore after suspend

On 11/30/2012 10:52 AM, Vincent Palatin wrote:
> When a cpu enters S3 state, the FPU state is lost.
> After resuming for S3, if we try to lazy restore the FPU for a process running
> on the same CPU, this will result in a corrupted FPU context.
> 
> We can just invalidate the "fpu_owner_task", so nobody will try to
> lazy restore a state which no longer exists in the hardware.
> 
> Tested with a 64-bit kernel on a 4-core Ivybridge CPU with eagerfpu=off,
> by doing thousands of suspend/resume cycles with 4 processes doing FPU
> operations running. Without the patch, a process is killed after a
> few hundreds cycles by a SIGFPE.
> 
> The issue seems to exist since 3.4 (after the FPU lazy restore was actually implemented),
> to apply the change to 3.4, "this_cpu_write" needs to be replaced by percpu_write.
> 
> Cc: Duncan Laurie <dlaurie@...omium.org>
> Cc: Olof Johansson <olofj@...omium.org>
> Cc: <stable@...nel.org> [v3.4+] # for 3.4 need to replace this_cpu_write by percpu_write
> Signed-off-by: Vincent Palatin <vpalatin@...omium.org>

Ouch!  Thank you for catching this!

	-hpa


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