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    SubjectRe: [PATCH 4/5] KVM: vmx: implement MSR_IA32_TSX_CTRL disable RTM functionality
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    On 05/12/19 00:49, Jim Mattson wrote:
    >> if (!boot_cpu_has(X86_FEATURE_RTM))
    >> - data &= ~ARCH_CAP_TAA_NO;
    >> + data &= ~(ARCH_CAP_TAA_NO | ARCH_CAP_TSX_CTRL_MSR);
    >> else if (!boot_cpu_has_bug(X86_BUG_TAA))
    >> data |= ARCH_CAP_TAA_NO;
    >> - else if (data & ARCH_CAP_TSX_CTRL_MSR)
    >> - data &= ~ARCH_CAP_MDS_NO;
    >>
    >> - /* KVM does not emulate MSR_IA32_TSX_CTRL. */
    >> - data &= ~ARCH_CAP_TSX_CTRL_MSR;
    > Shouldn't kvm be masking off any bits that it doesn't know about here?
    > Who knows what future features we may claim to support?

    Good question, in the past the ARCH_CAPABILITIES were just "we don't
    have this bug" so it made sense to pass everything through. Now we have
    TSX_CTRL that is of a different kind and arguably should have been a
    CPUID bit, so we should indeed mask unknown capabilties.

    Paolo

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