linux-kernel - Re: [PATCH v2 5/8] KVM: TDX: Handle TDG.VP.VMCALL<MapGPA>

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Message-ID: <Z6zu8liLTKAKmPwV@google.com>
Date: Wed, 12 Feb 2025 10:56:50 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
Cc: Chao Gao <chao.gao@...el.com>, Yan Zhao <yan.y.zhao@...el.com>, pbonzini@...hat.com, 
	kvm@...r.kernel.org, rick.p.edgecombe@...el.com, kai.huang@...el.com, 
	adrian.hunter@...el.com, reinette.chatre@...el.com, xiaoyao.li@...el.com, 
	tony.lindgren@...el.com, isaku.yamahata@...el.com, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/8] KVM: TDX: Handle TDG.VP.VMCALL<MapGPA>

On Wed, Feb 12, 2025, Binbin Wu wrote:
> On 2/12/2025 8:46 AM, Sean Christopherson wrote:
> > I am completely comfortable saying that KVM doesn't care about STI/SS shadows
> > outside of the HALTED case, and so unless I'm missing something, I think it makes
> > sense for tdx_protected_apic_has_interrupt() to not check RVI outside of the HALTED
> > case, because it's impossible to know if the interrupt is actually unmasked, and
> > statistically it's far, far more likely that it _is_ masked.
> OK. Will update tdx_protected_apic_has_interrupt() in "TDX interrupts" part.
> And use kvm_vcpu_has_events() to replace the open code in this patch.

Something to keep an eye on: kvm_vcpu_has_events() returns true if pv_unhalted
is set, and pv_unhalted is only cleared on transitions KVM_MP_STATE_RUNNABLE.
If the guest initiates a spurious wakeup, pv_unhalted could be left set in
perpetuity.

I _think_ this would work and is generally desirable?

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8e77e61d4fbd..435ca2782c3c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11114,9 +11114,6 @@ static bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu)
            kvm_apic_init_sipi_allowed(vcpu))
                return true;
 
-       if (vcpu->arch.pv.pv_unhalted)
-               return true;
-
        if (kvm_is_exception_pending(vcpu))
                return true;
 
@@ -11157,7 +11154,8 @@ static bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu)
 
 int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
 {
-       return kvm_vcpu_running(vcpu) || kvm_vcpu_has_events(vcpu);
+       return kvm_vcpu_running(vcpu) || vcpu->arch.pv.pv_unhalted ||
+              kvm_vcpu_has_events(vcpu);
 }
 
 /* Called within kvm->srcu read side.  */
@@ -11293,7 +11291,7 @@ static int __kvm_emulate_halt(struct kvm_vcpu *vcpu, int state, int reason)
         */
        ++vcpu->stat.halt_exits;
        if (lapic_in_kernel(vcpu)) {
-               if (kvm_vcpu_has_events(vcpu))
+               if (kvm_vcpu_has_events(vcpu) || vcpu->arch.pv.pv_unhalted)
                        vcpu->arch.pv.pv_unhalted = false;
                else
                        vcpu->arch.mp_state = state;