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Subject[PATCH v2 20/43] KVM: VMX: Skip Posted Interrupt updates if APICv is hard disabled
Explicitly skip posted interrupt updates if APICv is disabled in all of
KVM, or if the guest doesn't have an in-kernel APIC. The PI descriptor
is kept up-to-date if APICv is inhibited, e.g. so that re-enabling APICv
doesn't require a bunch of updates, but neither the module param nor the
APIC type can be changed on-the-fly.

Signed-off-by: Sean Christopherson <>
arch/x86/kvm/vmx/posted_intr.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
index 3263056784f5..351666c41bbc 100644
--- a/arch/x86/kvm/vmx/posted_intr.c
+++ b/arch/x86/kvm/vmx/posted_intr.c
@@ -28,11 +28,14 @@ void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
unsigned int dest;

- * In case of hot-plug or hot-unplug, we may have to undo
- * vmx_vcpu_pi_put even if there is no assigned device. And we
- * always keep PI.NDST up to date for simplicity: it makes the
- * code easier, and CPU migration is not a fast path.
+ * To simplify hot-plug and dynamic toggling of APICv, keep PI.NDST and
+ * PI.SN up-to-date even if there is no assigned device or if APICv is
+ * deactivated due to a dynamic inhibit bit, e.g. for Hyper-V's SyncIC.
+ if (!enable_apicv || !lapic_in_kernel(vcpu))
+ return;
+ /* Nothing to do if PI.SN==0 and the vCPU isn't being migrated. */
if (!pi_test_sn(pi_desc) && vcpu->cpu == cpu)

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