linux-kernel - Re: [CFT PATCH 2/2] KVM: x86: support XSAVES usage in the host

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Message-ID: <546FB57B.3000303@redhat.com>
Date:	Fri, 21 Nov 2014 22:58:19 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
CC:	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Fenghua Yu <fenghua.yu@...el.com>, stable@...r.kernel.org,
	Nadav Amit <namit@...technion.ac.il>
Subject: Re: [CFT PATCH 2/2] KVM: x86: support XSAVES usage in the host



On 21/11/2014 21:06, Andy Lutomirski wrote:
>> > +			cpuid_count(XSTATE_CPUID, index,
>> > +				    &size, &offset, &ecx, &edx);
>> > +	                memcpy(dest + offset, src, size);
> Is this really the best way to do this?  cpuid is serializing, so this
> is possibly *very* slow.

The data is in arch/x86/kernel/xsave.c, but it is not exported.  But
this is absolutely not a hotspot.

Paolo
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