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

[H. Peter Anvin]

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@xxxxxxxxxxxx>
> Cc: Olof Johansson <olofj@xxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxx> [v3.4+] # for 3.4 need to replace this_cpu_write by percpu_write
> Signed-off-by: Vincent Palatin <vpalatin@xxxxxxxxxxxx>

Ouch!  Thank you for catching this!

	-hpa


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