kvm: i8254: Deactivate APICv when using in-kernel PIT re-injection mode.

AMD SVM AVIC accelerates EOI write and does not trap. This causes
in-kernel PIT re-injection mode to fail since it relies on irq-ack
notifier mechanism. So, APICv is activated only when in-kernel PIT
is in discard mode e.g. w/ qemu option:

  -global kvm-pit.lost_tick_policy=discard

Also, introduce APICV_INHIBIT_REASON_PIT_REINJ bit to be used for this
reason.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 4a6dc54cc12b..b24c606ac04b 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -295,12 +295,24 @@ void kvm_pit_set_reinject(struct kvm_pit *pit, bool reinject)
 	if (atomic_read(&ps->reinject) == reinject)
 		return;
 
+	/*
+	 * AMD SVM AVIC accelerates EOI write and does not trap.
+	 * This cause in-kernel PIT re-inject mode to fail
+	 * since it checks ps->irq_ack before kvm_set_irq()
+	 * and relies on the ack notifier to timely queue
+	 * the pt->worker work iterm and reinject the missed tick.
+	 * So, deactivate APICv when PIT is in reinject mode.
+	 */
 	if (reinject) {
+		kvm_request_apicv_update(kvm, false,
+					 APICV_INHIBIT_REASON_PIT_REINJ);
 		/* The initial state is preserved while ps->reinject == 0. */
 		kvm_pit_reset_reinject(pit);
 		kvm_register_irq_ack_notifier(kvm, &ps->irq_ack_notifier);
 		kvm_register_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
 	} else {
+		kvm_request_apicv_update(kvm, true,
+					 APICV_INHIBIT_REASON_PIT_REINJ);
 		kvm_unregister_irq_ack_notifier(kvm, &ps->irq_ack_notifier);
 		kvm_unregister_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
 	}