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SubjectRe: [PATCH] KVM: nVMX: Don't expose TSC scaling to L1 when on Hyper-V
On Mon, Jun 13, 2022, Paolo Bonzini wrote:
> On 6/13/22 18:16, Anirudh Rayabharam wrote:
> > + if (!kvm_has_tsc_control)
> > + msrs->secondary_ctls_high &= ~SECONDARY_EXEC_TSC_SCALING;
> > +
> > msrs->secondary_ctls_low = 0;
> > msrs->secondary_ctls_high &=
> > SECONDARY_EXEC_DESC |
> > @@ -6667,8 +6670,7 @@ void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps)
> > SECONDARY_EXEC_RDRAND_EXITING |
> > SECONDARY_EXEC_ENABLE_INVPCID |
> > SECONDARY_EXEC_RDSEED_EXITING |
> > - SECONDARY_EXEC_XSAVES |
> > - SECONDARY_EXEC_TSC_SCALING;
> > + SECONDARY_EXEC_XSAVES;
> > /*
>
> This is wrong because it _always_ disables SECONDARY_EXEC_TSC_SCALING,
> even if kvm_has_tsc_control == true.
>
> That said, I think a better implementation of this patch is to just add
> a version of evmcs_sanitize_exec_ctrls that takes a struct
> nested_vmx_msrs *, and call it at the end of nested_vmx_setup_ctl_msrs like
>
> evmcs_sanitize_nested_vmx_vsrs(msrs);

Any reason not to use the already sanitized vmcs_config? I can't think of any
reason why the nested path should blindly use the raw MSR values from hardware.

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