Re: [RFC PATCH v3 28/59] KVM: x86: Check for pending APICv interrupt in kvm_vcpu_has_events()

[Sean Christopherson]

On Thu, Nov 25, 2021, Paolo Bonzini wrote:
> On 11/25/21 01:20, isaku.yamahata@xxxxxxxxx wrote:
> > From: Sean Christopherson<sean.j.christopherson@xxxxxxxxx>
> > 
> > Return true for kvm_vcpu_has_events() if the vCPU has a pending APICv
> > interrupt to support TDX's usage of APICv.  Unlike VMX, TDX doesn't have
> > access to vmcs.GUEST_INTR_STATUS and so can't emulate posted interrupts,
> > i.e. needs to generate a posted interrupt and more importantly can't
> > manually move requested interrupts into the vIRR (which it also doesn't
> > have access to).
> 
> Does this mean it is impossible to disable APICv on TDX?  If so, please add
> a WARN.

Yes, APICv is forced.

Rereading this patch, checking only for a pending posted interrupt isn't correct,
a pending interrupt that's below the PPR shouldn't be considered a wake event.

A much better approach would be to have vt_sync_pir_to_irr() redirect to a TDX
implementation to read the PIR but not update the vIRR, that way common x86 doesn't
need to be touched.  Hopefully that can be done in a race-free way.