KVM: i8259: initialize isr_ack

isr_ack is never initialized.  So, until the first PIC reset, interrupts
may fail to be injected.  This can cause Windows XP to fail to boot, as
reported in the fallout from the fix to
https://bugzilla.kernel.org/show_bug.cgi?id=21962.

Reported-and-tested-by: Nicolas Prochazka <[email protected]>
Signed-off-by: Avi Kivity <[email protected]>

Author: avikivity

arch/x86/kvm/i8259.c

@@ -575,6 +575,8 @@ struct kvm_pic *kvm_create_pic(struct kvm *kvm)
 	s->pics[1].elcr_mask = 0xde;
 	s->pics[0].pics_state = s;
 	s->pics[1].pics_state = s;
+	s->pics[0].isr_ack = 0xff;
+	s->pics[1].isr_ack = 0xff;
 
 	/*
 	 * Initialize PIO device