Re: [PATCH 1/3] KVM: nVMX: Move 'nested_run' counter to enter_guest_mode()

[Sean Christopherson <seanjc@google.com>]

On Tue, May 11, 2021, Krish Sadhukhan wrote:
> Move 'nested_run' counter to enter_guest_mode() because,
>     i) This counter is common to both Intel and AMD and can be incremented
>        from a common place,
>     ii) guest mode is a more finer-grained state than the beginning of
> 	nested_svm_vmrun() and nested_vmx_run().

Hooking enter_guest_mode() makes the name a misnomer since it will count cases
such as setting nested state and resuming from SMI, neither of which is a nested
run in the sense of L1 deliberately choosing to run L2.

And while bumping nested_run at the very beginning of VMLAUNCH/VMRESUME/VMRUN is
arguably wrong in that it counts _attempts_ instead of successful VM-Enters, it's
at least consistent.  Moving this to enter_guest_mode() means it's arbitrarily
counting VM-Enter that fails late, but not those that fail early.

If we really want it to mean "successful VM-Enter", then we should wait until
after VM-Enter actual succeeds, and do it only for actual VM-Enter.