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

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Message-ID: <483630AE.3050905@zytor.com>
Date:	Thu, 22 May 2008 19:49:18 -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:
>> hmm.. so the kernel needs to export all the cpuid info (that the kernel
>> enables and supports) to the user through some mechanism then?
> 
> For a cheap interface, we use AT_HWCAP for this.  Unfortunately that only
> covers the first 32 bits of CPUID info.  (For another cheap interface,
> giving all the CPUID bits in the vDSO would be easy.)
> 
> For a clunky interface that already exists and is "simple" to use,
> there is /dev/cpu/0/cpuid now.  I wonder if having a device node and
> opening it too much for applications that consider the vDSO too complex.

I doubt it.

	-hpa

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