Re: [PATCH v3 3/7] KVM: nVMX: Make an event request when pending an MTF nested VM-Exit

[Paolo Bonzini]

On 8/22/22 19:52, Jim Mattson wrote:
> On Mon, Aug 22, 2022 at 10:08 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> > From: Sean Christopherson <seanjc@xxxxxxxxxx>
> >
> > Set KVM_REQ_EVENT when MTF becomes pending to ensure that KVM will run
> > through inject_pending_event() and thus vmx_check_nested_events() prior
> > to re-entering the guest.
> >
> > MTF currently works by virtue of KVM's hack that calls
> > kvm_check_nested_events() from kvm_vcpu_running(), but that hack will
> > be removed in the near future.  Until that call is removed, the patch
> > introduces no functional change.
> >
> > Fixes: 5ef8acbdd687 ("KVM: nVMX: Emulate MTF when performing instruction emulation")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > ---
> What happens if live migration occurs before the KVM_REQ_EVENT is processed?

Good point, this must be squashed in:

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index ab135f9ef52f..a703b71d675d 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -6481,6 +6481,8 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
 	if (ret)
 		goto error_guest_mode;
 
+	if (vmx->nested.mtf_pending)
+		kvm_make_request(KVM_REQ_EVENT, vcpu);
 	return 0;
 
 error_guest_mode:

so that the other side restores the request.

Paolo