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SubjectRe: [PATCH v5 4/5] KVM: VMX: Allow direct access to MSR_IA32_SPEC_CTRL
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On Wed, 2018-01-31 at 13:05 -0800, Jim Mattson wrote:
> On Wed, Jan 31, 2018 at 1:00 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> > Yes, but how would moving the field into struct loaded_vmcs do anything?
> >  Only vmon/vmoff would change anything in vmx->nested.vmcs02.
>
> My suggestion was that nested_vmx_merge_msr_bitmap should set the
> vmcs02 version of save_spec_ctrl_on_exit based on the calculated value
> of the write permission bit for IA32_SPEC_CTRL in the vmcs02 MSR
> permission bitmap.
>
> > Even then, L1 vmexits will also be penalized because L1 has probably
> > done an RDMSR/WRMSR on L2->L1 vmexit.  So I don't think it's an issue?
>
> Yes, it sucks to be L1 in this situation.

Well... we *could* clear the save_spec_ctrl_on_exit flag and intercept
the MSR again, any time that the actual value of spec_ctrl is zero. 

I don't think we'd want to do that too aggressively, but there might be
something we could do there.[unhandled content-type:application/x-pkcs7-signature]
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