linux-kernel - Re: [PATCH] KVM: VMX: enable LBR virtualization

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Date:	Wed, 14 Oct 2015 13:30:16 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Jian Zhou <jianjay.zhou@...wei.com>, herongguang.he@...wei.com,
	zhang.zhanghailiang@...wei.com, gleb@...nel.org,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	weidong.huang@...wei.com, peter.huangpeng@...wei.com
Subject: Re: [PATCH] KVM: VMX: enable LBR virtualization



On 14/10/2015 13:26, Jian Zhou wrote:
> On 12/10/2015 20:44, Paolo Bonzini wrote:
>> In addition, the MSR numbers may differ between the guest and the host,
>> because it is possible to emulate e.g. a Core CPU on a Core 2 CPU.  So I
>> recommend against using the atomic switch mechanism for the from/to MSRs.
> 
>   The vLBR feature depends on vPMU, and to enable vPMU, it needs to
>   specify the "cpu mode" in the guest XML as host-passthrough. I think
>   the MSR numbers between the guest and the host are the same in this
>   senario.

Does it depend on vPMU _for Linux guests_ or in general?  My impression
is that LBR can be used by the guest independent of the PMU.  You should
also write a unit test for kvm-unit-tests to test the behavior of your
implementation.

Thanks,

Paolo
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