linux-kernel - Re: [PATCH 1/1] KVM: nVMX: update VPPR on vmlaunch/vmresume

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Message-ID: <Zu0vvRyCyUaQ2S2a@google.com>
Date: Fri, 20 Sep 2024 01:18:05 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: "Markku Ahvenjärvi" <mankku@...il.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, janne.karhunen@...il.com, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] KVM: nVMX: update VPPR on vmlaunch/vmresume

On Fri, Sep 20, 2024, Markku Ahvenjärvi wrote:
> Running certain hypervisors under KVM on VMX suffered L1 hangs after
> launching a nested guest. The external interrupts were not processed on
> vmlaunch/vmresume due to stale VPPR, and L2 guest would resume without
> allowing L1 hypervisor to process the events.
> 
> The patch ensures VPPR to be updated when checking for pending
> interrupts.

This is architecturally incorrect, PPR isn't refreshed at VM-Enter.

Aha!  I wonder if the missing PPR update is due to the nested VM-Enter path
directly clearing IRR when processing a posted interrupt.

On top of https://github.com/kvm-x86/linux/tree/next, does this fix things?

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index a8e7bc04d9bf..a8255c6f0d51 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3731,7 +3731,7 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
            kvm_apic_has_interrupt(vcpu) == vmx->nested.posted_intr_nv) {
                vmx->nested.pi_pending = true;
                kvm_make_request(KVM_REQ_EVENT, vcpu);
-               kvm_apic_clear_irr(vcpu, vmx->nested.posted_intr_nv);
+               kvm_apic_ack_interrupt(vcpu, vmx->nested.posted_intr_nv);
        }
 
        /* Hide L1D cache contents from the nested guest.  */