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From: Paolo Bonzini <pbonzini@redhat.com>
To: Chao Peng <chao.p.peng@linux.intel.com>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org,
	Eduardo Habkost <ehabkost@redhat.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH] target-i386: kvm: cache KVM_GET_SUPPORTED_CPUID data
Date: Tue, 14 Jun 2016 10:21:41 +0200	[thread overview]
Message-ID: <7ce88285-2d4c-7b4a-767a-7e6c9eb25f2b@redhat.com> (raw)
In-Reply-To: <20160614050128.GA21465@pengc-linux.bj.intel.com>



On 14/06/2016 07:01, Chao Peng wrote:
>> > 
>> > Which are the CPUID leaves for which KVM_GET_SUPPORTED_CPUID is not
>> > stateless?  I cannot find any.
> I have though leaf 0xd, sub leaf 1 is not stateless, as the size of
> xsave buffer(EBX) is based on XCR0 | IA32_XSS. But after looking KVM
> code more carefully, seems I was wrong. The code calculates EBX with the
> host xcr0 but not guest xcr0, nor guest IA32_XSS (not sure if this is
> the correct behavior), so it can always returns constant data on a
> certain machine.

Indeed, KVM computes the correct value at runtime, but
KVM_GET_SUPPORTED_CPUID runs before there is a value for guest XCR0 or
guest IA32_XSS.

Thanks, I've queued the patch for QEMU 2.7.

Paolo

WARNING: multiple messages have this Message-ID (diff)
From: Paolo Bonzini <pbonzini@redhat.com>
To: Chao Peng <chao.p.peng@linux.intel.com>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org,
	Eduardo Habkost <ehabkost@redhat.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Richard Henderson <rth@twiddle.net>
Subject: Re: [Qemu-devel] [PATCH] target-i386: kvm: cache KVM_GET_SUPPORTED_CPUID data
Date: Tue, 14 Jun 2016 10:21:41 +0200	[thread overview]
Message-ID: <7ce88285-2d4c-7b4a-767a-7e6c9eb25f2b@redhat.com> (raw)
In-Reply-To: <20160614050128.GA21465@pengc-linux.bj.intel.com>



On 14/06/2016 07:01, Chao Peng wrote:
>> > 
>> > Which are the CPUID leaves for which KVM_GET_SUPPORTED_CPUID is not
>> > stateless?  I cannot find any.
> I have though leaf 0xd, sub leaf 1 is not stateless, as the size of
> xsave buffer(EBX) is based on XCR0 | IA32_XSS. But after looking KVM
> code more carefully, seems I was wrong. The code calculates EBX with the
> host xcr0 but not guest xcr0, nor guest IA32_XSS (not sure if this is
> the correct behavior), so it can always returns constant data on a
> certain machine.

Indeed, KVM computes the correct value at runtime, but
KVM_GET_SUPPORTED_CPUID runs before there is a value for guest XCR0 or
guest IA32_XSS.

Thanks, I've queued the patch for QEMU 2.7.

Paolo

  reply	other threads:[~2016-06-14  8:21 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-13  2:21 [PATCH] target-i386: kvm: cache KVM_GET_SUPPORTED_CPUID data Chao Peng
2016-06-13  2:21 ` [Qemu-devel] " Chao Peng
2016-06-13 10:02 ` Paolo Bonzini
2016-06-13 10:02   ` [Qemu-devel] " Paolo Bonzini
2016-06-14  5:01   ` Chao Peng
2016-06-14  5:01     ` [Qemu-devel] " Chao Peng
2016-06-14  8:21     ` Paolo Bonzini [this message]
2016-06-14  8:21       ` Paolo Bonzini
2016-06-14  8:31       ` Chao Peng
2016-06-14  8:31         ` [Qemu-devel] " Chao Peng

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