linux-kernel - Re: [RFC] x86: xsave/xrstor support, ucontext

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Date:	Wed, 21 May 2008 18:38:31 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Roland McGrath <roland@...hat.com>
CC:	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mikael Pettersson <mikpe@...uu.se>,
	Andi Kleen <andi@...stfloor.org>, mingo@...e.hu,
	tglx@...utronix.de, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, drepper@...hat.com,
	Hongjiu.lu@...el.com, linux-kernel@...r.kernel.org,
	arjan@...ux.intel.com, rmk+lkml@....linux.org.uk, dan@...ian.org,
	asit.k.mallick@...el.com
Subject: Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions

Roland McGrath wrote:
>> The biggest potential problem with this that I see is that relying on 
>> CPUID can mess with certain virtualization solutions.  Another option to 
>> accomplish the same thing would be to have a system call (preferrably a 
>> prctl, since it is at least in theory personality-dependent) to query 
>> what information is included in the fpstate data - since it will always 
>> be the same for any particular kernel.
> 
> It's easy and cheap to add an indicator to the vDSO for this.

Yes, but I suspect for legacy apps running without vDSO might matter.

	-hpa
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