linux-kernel - Re: [PATCH 3/6] x86, kvm: use kernel_fpu_begin/end() in kvm_load/put_guest

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Message-ID: <505A002E.6050304@zytor.com>
Date:	Wed, 19 Sep 2012 10:26:06 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Suresh Siddha <suresh.b.siddha@...el.com>, mingo@...nel.org,
	torvalds@...ux-foundation.org, andreas.herrmann3@....com,
	bp@...64.org, robert.richter@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] x86, kvm: use kernel_fpu_begin/end() in kvm_load/put_guest_fpu()

On 09/19/2012 10:22 AM, Avi Kivity wrote:
> 
> Note, we could also go in a different direction and make
> kernel_fpu_begin() use preempt notifiers and thus make its users
> preemptible.  But that's for a separate patchset.
> 

Where would you put the state if you were preempted?  You want to
allocate a full extra buffer for the kernel xstate for each thread just
in case?  ("Yes" is a valid answer to that question, but it is a fair
chunk of memory.)

	-hpa

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