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    SubjectRe: [PATCH] kvm/x86/vmx: Make the emulation of MSR_IA32_ARCH_CAPABILITIES only for vmx
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    On Thu, 2019-03-07 at 19:15 +0100, Paolo Bonzini wrote:
    > On 07/03/19 18:37, Sean Christopherson wrote:
    > > On Thu, Mar 07, 2019 at 05:31:43PM +0800, Xiaoyao Li wrote:
    > > > At present, we report F(ARCH_CAPABILITIES) for x86 arch(both vmx and svm)
    > > > unconditionally, but we only emulate this MSR in vmx. It will cause #GP
    > > > while guest kernel rdmsr(MSR_IA32_ARCH_CAPABILITIES) in an AMD host.
    > > >
    > > > Since MSR IA32_ARCH_CAPABILITIES is an intel-specific MSR, it makes no
    > > > sense to emulate it in svm. Thus this patch chooses to only emulate it
    > > > for vmx, and moves the related handling to vmx related files.
    > >
    > > What about emulating the MSR on an AMD host for testing purpsoes? It
    > > might be a useful way for someone without Intel hardware to test spectre
    > > related flows.
    > >
    > > In other words, an alternative to restricting emulation of the MSR to
    > > Intel CPUS would be to move MSR_IA32_ARCH_CAPABILITIES handling into
    > > kvm_{get,set}_msr_common(). Guest access to MSR_IA32_ARCH_CAPABILITIES
    > > is gated by X86_FEATURE_ARCH_CAPABILITIES in the guest's CPUID, e.g.
    > > RDMSR will naturally #GP fault if userspace passes through the host's
    > > CPUID on a non-Intel system.
    >
    > This is also better because it wouldn't change the guest ABI for AMD
    > processors. Dropping CPUID flags is generally not a good idea.
    >
    > Paolo

    Hi, Paolo and Sean,

    OK, as you think it's better to emulate MSR ARCH_CAPABILITIES on all x86 host,
    so should I make the same to MSR CORE_CAPABILITY?

    If so, I will make it for our v5 patches of split lock detection to emualte MSR
    CORE_CAPABILITY in this way.

    Thanks,
    Xiaoyao


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