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SubjectRe: [PATCH v2] kvm: nVMX: Introduce KVM_CAP_STATE
On Mon, Apr 9, 2018 at 1:37 AM, KarimAllah Ahmed <karahmed@amazon.de> wrote:

> + /*
> + * Force a nested exit that guarantees that any state capture
> + * afterwards by any IOCTLs (MSRs, etc) will not capture a mix of L1
> + * and L2 state.
> + *
> + * One example where that would lead to an issue is the TSC DEADLINE
> + * MSR vs the guest TSC. If the L2 guest is running, the guest TSC will
> + * be the L2 TSC while the TSC deadline MSR will contain the L1 TSC
> + * deadline MSR. That would lead to a very large (and wrong) "expire"
> + * diff when LAPIC is initialized during instance restore (i.e. the
> + * instance will appear to have hanged!).
> + */

This sounds like a bug in the virtualization of IA32_TSC_DEADLINE.
Without involving save/restore, what happens if L2 sets
IA32_TSC_DEADLINE (and L1 permits it via the MSR permission bitmap)?
The IA32_TSC_DEADLINE MSR is always specified with respect to L1's
time domain.

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