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SubjectRe: [PATCH 08/12] KVM: nSVM: Use KVM-governed feature framework to track "vVM{SAVE,LOAD} enabled"
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On Tue, Feb 21, 2023, Yu Zhang wrote:
> > Sorry, why guest_cpuid_is_intel(vcpu)? Is it becasue that a AMD host with virtual
> > VMSAVE/VMLOAD capability will always expose this feature for all AMD guests?
>
> Oh, sorry. I missed the guest_cpuid_has() in kvm_governed_feature_check_and_set().
> So please just ignore my 2nd question.
>
> As to the check of guest_cpuid_is_intel(), is it necessary?

Yes? The comment in init_vmcb_after_set_cpuid() says:

/*
* We must intercept SYSENTER_EIP and SYSENTER_ESP
* accesses because the processor only stores 32 bits.
* For the same reason we cannot use virtual VMLOAD/VMSAVE.
*/

but I'm struggling to connect the dots to SYSENTER. I suspect the comment is
misleading and has nothing to do 32-bit vs. 64-bit (or I'm reading it wrong) and
should be something like:

/*
* Disable virtual VMLOAD/VMSAVE and intercept VMLOAD/VMSAVE if the
* guest CPU is Intel in order to inject #UD.
*/

In other words, a non-SVM guest shouldn't be allowed to execute VMLOAD/VMSAVE.

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