KVM: PIC: enhance IPI avoidance

The PIC code makes little effort to avoid kvm_vcpu_kick(), resulting in
unnecessary guest exits in some conditions.

For example, if the timer interrupt is routed through the IOAPIC, IRR
for IRQ 0 will get set but not cleared, since the APIC is handling the
acks.

This means that everytime an interrupt < 16 is triggered, the priority
logic will find IRQ0 pending and send an IPI to vcpu0 (in case IRQ0 is
not masked, which is Linux's case).

Introduce a new variable isr_ack to represent the IRQ's for which the
guest has been signalled / cleared the ISR. Use it to avoid more than
one IPI per trigger-ack cycle, in addition to the avoidance when ISR is
set in get_priority().

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/x86/kvm/irq.h b/arch/x86/kvm/irq.h
index 479a3d2..4748532 100644
--- a/arch/x86/kvm/irq.h
+++ b/arch/x86/kvm/irq.h
@@ -42,6 +42,7 @@ struct kvm_kpic_state {
 	u8 irr;		/* interrupt request register */
 	u8 imr;		/* interrupt mask register */
 	u8 isr;		/* interrupt service register */
+	u8 isr_ack;	/* interrupt ack detection */
 	u8 priority_add;	/* highest irq priority */
 	u8 irq_base;
 	u8 read_reg_select;
@@ -70,6 +71,7 @@ struct kvm_pic *kvm_create_pic(struct kvm *kvm);
 void kvm_pic_set_irq(void *opaque, int irq, int level);
 int kvm_pic_read_irq(struct kvm *kvm);
 void kvm_pic_update_irq(struct kvm_pic *s);
+void kvm_pic_clear_isr_ack(struct kvm *kvm);
 
 static inline struct kvm_pic *pic_irqchip(struct kvm *kvm)
 {