Re: AVIC related warning in enable_irq_window

[Suravee Suthikulpanit]

Paolo / Maxim,

On 5/4/20 4:25 PM, Paolo Bonzini wrote:
> On 04/05/20 11:13, Maxim Levitsky wrote:
> > On Mon, 2020-05-04 at 15:46 +0700, Suravee Suthikulpanit wrote:
> > > Paolo / Maxim,
> > >
> > > On 5/2/20 11:42 PM, Paolo Bonzini wrote:
> > > > On 02/05/20 15:58, Maxim Levitsky wrote:
> > > > > The AVIC is disabled by svm_toggle_avic_for_irq_window, which calls
> > > > > kvm_request_apicv_update, which broadcasts the KVM_REQ_APICV_UPDATE vcpu request,
> > > > > however it doesn't broadcast it to CPU on which now we are running, which seems OK,
> > > > > because the code that handles that broadcast runs on each VCPU entry, thus
> > > > > when this CPU will enter guest mode it will notice and disable the AVIC.
> > > > >
> > > > > However later in svm_enable_vintr, there is test 'WARN_ON(kvm_vcpu_apicv_active(&svm->vcpu));'
> > > > > which is still true on current CPU because of the above.
> > > >
> > > > Good point!  We can just remove the WARN_ON I think.  Can you send a patch?
> > >
> > > Instead, as an alternative to remove the WARN_ON(), would it be better to just explicitly
> > > calling kvm_vcpu_update_apicv(vcpu) to update the apicv_active flag right after
> > > kvm_request_apicv_update()?
> > This should work IMHO, other that the fact kvm_vcpu_update_apicv will be called again,
> > when this vcpu is entered since the KVM_REQ_APICV_UPDATE will still be pending on it.
> > It shoudn't be a problem, and we can even add a check to do nothing when it is called
> > while avic is already in target enable state.
>
> I thought about that but I think it's a bit confusing.  If we want to
> keep the WARN_ON, Maxim can add an equivalent one to svm_vcpu_run, which
> is even better because the invariant is clearer.
>
> WARN_ON((vmcb->control.int_ctl & (AVIC_ENABLE_MASK | V_IRQ_MASK))
> 	== (AVIC_ENABLE_MASK | V_IRQ_MASK));
>
> Paolo

Quick update. I tried your suggestion as following, and it's showing the warning still.
I'll look further into this.

 arch/x86/kvm/svm/svm.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 2f379ba..142c4b9 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1368,9 +1368,6 @@ static inline void svm_enable_vintr(struct vcpu_svm *svm)
 {
        struct vmcb_control_area *control;

-       /* The following fields are ignored when AVIC is enabled */
-       WARN_ON(kvm_vcpu_apicv_active(&svm->vcpu));
-
        /*
         * This is just a dummy VINTR to actually cause a vmexit to happen.
         * Actual injection of virtual interrupts happens through EVENTINJ.
@@ -3322,6 +3319,11 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
                vcpu->arch.apic->lapic_timer.timer_advance_ns)
                kvm_wait_lapic_expire(vcpu);

+//SURAVEE
+       WARN_ON((svm->vmcb->control.int_ctl &
+                (AVIC_ENABLE_MASK | V_IRQ_MASK))
+                == (AVIC_ENABLE_MASK | V_IRQ_MASK));
+

Suravee