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

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Message-ID: <20080523180928.GE18385@linux-os.sc.intel.com>
Date:	Fri, 23 May 2008 11:09:28 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Roland McGrath <roland@...hat.com>,
	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

On Thu, May 22, 2008 at 07:49:18PM -0700, H. Peter Anvin wrote:
> 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.

Ok. If really needed, they can use this interface aswell. But I don't
see a need for a new system call / other mechanism, just for xsave
purpose. They can rely on cpuid or any other equivalent infrastructure the
kernel provides.

thanks,
suresh
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