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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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