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Date: Thu, 22 May 2008 19:49:18 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Roland McGrath <roland@redhat.com>
CC: Suresh Siddha <suresh.b.siddha@intel.com>,
       Mikael Pettersson <mikpe@it.uu.se>, Andi Kleen <andi@firstfloor.org>,
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       linux-kernel@vger.kernel.org, arjan@linux.intel.com,
       rmk+lkml@arm.linux.org.uk, dan@debian.org, asit.k.mallick@intel.com
Subject: Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions
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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