linux-kernel - [PATCH 1/5] KVM: nVMX: Explicitly update vPPR on successful nested VM-Enter

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Message-ID: <20241101191447.1807602-2-seanjc@google.com>
Date: Fri,  1 Nov 2024 12:14:43 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Chao Gao <chao.gao@...el.com>
Subject: [PATCH 1/5] KVM: nVMX: Explicitly update vPPR on successful nested VM-Enter

Always request pending event evaluation after successful nested VM-Enter
if L1 has a pending IRQ, as KVM will effectively do so anyways when APICv
is enabled, by way of vmx_has_apicv_interrupt().  This will allow dropping
the aforementioned APICv check, and will also allow handling nested Posted
Interrupt processing entirely within vmx_check_nested_events(), which is
necessary to honor priority between concurrent events.

Note, checking for pending IRQs has a subtle side effect, as it results in
a PPR update for L1's vAPIC (PPR virtualization does happen at VM-Enter,
but for nested VM-Enter that affects L2's vAPIC, not L1's vAPIC).  However,
KVM updates PPR _constantly_, even when PPR technically shouldn't be
refreshed, e.g. kvm_vcpu_has_events() re-evaluates PPR if IRQs are
unblocked, by way of the same kvm_apic_has_interrupt() check.  Ditto for
nested VM-Enter itself, when nested posted interrupts are enabled.  Thus,
trying to avoid a PPR update on VM-Enter just to be pedantically accurate
is ridiculous, given the behavior elsewhere in KVM.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/nested.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 746cb41c5b98..84386329474b 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3604,7 +3604,8 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
 	 * effectively unblock various events, e.g. INIT/SIPI cause VM-Exit
 	 * unconditionally.
 	 */
-	if (unlikely(evaluate_pending_interrupts))
+	if (unlikely(evaluate_pending_interrupts) ||
+	    kvm_apic_has_interrupt(vcpu))
 		kvm_make_request(KVM_REQ_EVENT, vcpu);

 	/*
-- 
2.47.0.163.g1226f6d8fa-goog