linux-kernel - Re: [PATCH v2 4/4] KVM: x86: Expose Architectural LBR CPUID and its XSAVES bit

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Message-ID: <7698fd6c-94da-e352-193f-e09e002a8961@redhat.com>
Date:   Fri, 5 Feb 2021 12:00:59 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Xu, Like" <like.xu@...el.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Like Xu <like.xu@...ux.intel.com>
Subject: Re: [PATCH v2 4/4] KVM: x86: Expose Architectural LBR CPUID and its
 XSAVES bit

On 05/02/21 09:16, Xu, Like wrote:
> Hi Paolo,
> 
> I am wondering if it is acceptable for you to
> review the minor Architecture LBR patch set without XSAVES for v5.12 ?
> 
> As far as I know, the guest Arch LBR  can still work without XSAVES 
> support.

I dopn't think it can work.  You could have two guests on the same 
physical CPU and the MSRs would be corrupted if the guests write to the 
MSR but they do not enable the LBRs.

Paolo