linux-kernel - Re: [Xen-devel] [PATCHv1] x86: don't schedule when handling #NM exception

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Message-ID: <5326761D.5000905@prgmr.com>
Date:	Sun, 16 Mar 2014 21:12:13 -0700
From:	Sarah Newman <srn@...mr.com>
To:	"H. Peter Anvin" <hpa@...or.com>,
	David Vrabel <david.vrabel@...rix.com>
CC:	Suresh Siddha <sbsiddha@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xen.org
Subject: Re: [Xen-devel] [PATCHv1] x86: don't schedule when handling #NM exception

On 03/16/2014 08:43 PM, H. Peter Anvin wrote:
> On 03/16/2014 08:35 PM, Sarah Newman wrote:
>> Can you please review my patch first?  It's only enabled when absolutely required.
> 
> It doesn't help.  It means you're running on Xen, and you will have
> processes subjected to random SIGKILL because they happen to touch the
> FPU when the atomic pool is low.
> 
> However, there is probably a happy medium: you don't actually need eager
> FPU restore, you just need eager FPU *allocation*.  We have been
> intending to allocate the FPU state at task creation time for eagerfpu,
> and Suresh Siddha has already produced such a patch; it just needs some
> minor fixups due to an __init failure.
> 
> http://lkml.kernel.org/r/1391325599.6481.5.camel@europa
> 
> In the Xen case we could turn on eager allocation but not eager fpu.  In
> fact, it might be justified to *always* do eager allocation...

Unconditional eager allocation works. Can xen users count on this being included and applied to the
stable kernels?

Thanks, Sarah
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