[PATCH v2 2/3] KVM: SVM: Don't update IRTEs if APICv/AVIC is disable

Sean Christopherson
2025-03-20T14:20:28Z

Skip IRTE updates if AVIC is disabled/unsupported, as forcing the IRTE
into remapped mode (kvm_vcpu_apicv_active() will never be true) is
unnecessary and wasteful. The IOMMU driver is responsible for putting
IRTEs into remapped mode when an IRQ is allocated by a device, long before
that device is assigned to a VM. I.e. the kernel as a whole has major
issues if the IRTE isn't already in remapped mode.

Opportunsitically kvm_arch_has_irq_bypass() to query for APICv/AVIC, so
so that all checks in KVM x86 incorporate the same information.

Cc: Yosry Ahmed <yosry.ahmed@linux.dev>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/svm/avic.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 65fd245a9953..901d8d2dc169 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -898,8 +898,7 @@ int avic_pi_update_irte(struct kvm *kvm, unsigned int host_irq,
struct kvm_irq_routing_table *irq_rt;
int idx, ret = 0;

- if (!kvm_arch_has_assigned_device(kvm) ||
- !irq_remapping_cap(IRQ_POSTING_CAP))
+ if (!kvm_arch_has_assigned_device(kvm) || !kvm_arch_has_irq_bypass())
return 0;

pr_debug("SVM: %s: host_irq=%#x, guest_irq=%#x, set=%#x\n",
--
2.49.0.395.g12beb8f557-goog