linux-kernel - [PATCH v2 52/59] KVM: VMX: WARN if VT-d Posted IRQs aren't possible when starting IRQ bypass

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Message-ID: <20250523010004.3240643-53-seanjc@google.com>
Date: Thu, 22 May 2025 17:59:57 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Joerg Roedel <joro@...tes.org>, David Woodhouse <dwmw2@...radead.org>, 
	Lu Baolu <baolu.lu@...ux.intel.com>
Cc: kvm@...r.kernel.org, iommu@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	Sairaj Kodilkar <sarunkod@....com>, Vasant Hegde <vasant.hegde@....com>, 
	Maxim Levitsky <mlevitsk@...hat.com>, Joao Martins <joao.m.martins@...cle.com>, 
	Francesco Lavra <francescolavra.fl@...il.com>, David Matlack <dmatlack@...gle.com>
Subject: [PATCH v2 52/59] KVM: VMX: WARN if VT-d Posted IRQs aren't possible
 when starting IRQ bypass

WARN if KVM attempts to "start" IRQ bypass when VT-d Posted IRQs are
disabled, to make it obvious that the logic is a sanity check, and so that
a bug related to nr_possible_bypass_irqs is more like to cause noisy
failures, e.g. so that KVM doesn't silently fail to wake blocking vCPUs.

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

diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
index 5671d59a6b6d..4a6d9a17da23 100644
--- a/arch/x86/kvm/vmx/posted_intr.c
+++ b/arch/x86/kvm/vmx/posted_intr.c
@@ -296,7 +296,7 @@ bool pi_has_pending_interrupt(struct kvm_vcpu *vcpu)
  */
 void vmx_pi_start_bypass(struct kvm *kvm)
 {
-	if (!kvm_arch_has_irq_bypass())
+	if (WARN_ON_ONCE(!vmx_can_use_vtd_pi(kvm)))
 		return;
 
 	kvm_make_all_cpus_request(kvm, KVM_REQ_UNBLOCK);
-- 
2.49.0.1151.ga128411c76-goog