KVM: PIT support for HPET legacy mode

When kvm is in hpet_legacy_mode, the hpet is providing the timer
interrupt and the pit should not be. So in legacy mode, the pit timer
is destroyed, but the *state* of the pit is maintained. So if kvm or
the guest tries to modify the state of the pit, this modification is
accepted, *except* that the timer isn't actually started. When we exit
hpet_legacy_mode, the current state of the pit (which is up to date
since we've been accepting modifications) is used to restart the pit
timer.

The saved_mode code in kvm_pit_load_count temporarily changes mode to
0xff in order to destroy the timer, but then restores the actual
value, again maintaining "current" state of the pit for possible later
reenablement.

[avi: add some reserved storage in the ioctl; make SET_PIT2 IOW]
[marcelo: fix memory corruption due to reserved storage]

Signed-off-by: Beth Kon <eak@us.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 18 insertions, 4 deletions

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 8c3ac30ef9b..9b62c57ba6e 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -332,20 +332,33 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
 	case 1:
         /* FIXME: enhance mode 4 precision */
 	case 4:
-		create_pit_timer(ps, val, 0);
+		if (!(ps->flags & KVM_PIT_FLAGS_HPET_LEGACY)) {
+			create_pit_timer(ps, val, 0);
+		}
 		break;
 	case 2:
 	case 3:
-		create_pit_timer(ps, val, 1);
+		if (!(ps->flags & KVM_PIT_FLAGS_HPET_LEGACY)){
+			create_pit_timer(ps, val, 1);
+		}
 		break;
 	default:
 		destroy_pit_timer(&ps->pit_timer);
 	}
 }
 
-void kvm_pit_load_count(struct kvm *kvm, int channel, u32 val)
+void kvm_pit_load_count(struct kvm *kvm, int channel, u32 val, int hpet_legacy_start)
 {
-	pit_load_count(kvm, channel, val);
+	u8 saved_mode;
+	if (hpet_legacy_start) {
+		/* save existing mode for later reenablement */
+		saved_mode = kvm->arch.vpit->pit_state.channels[0].mode;
+		kvm->arch.vpit->pit_state.channels[0].mode = 0xff; /* disable timer */
+		pit_load_count(kvm, channel, val);
+		kvm->arch.vpit->pit_state.channels[0].mode = saved_mode;
+	} else {
+		pit_load_count(kvm, channel, val);
+	}
 }
 
 static inline struct kvm_pit *dev_to_pit(struct kvm_io_device *dev)
@@ -554,6 +567,7 @@ void kvm_pit_reset(struct kvm_pit *pit)
 	struct kvm_kpit_channel_state *c;
 
 	mutex_lock(&pit->pit_state.lock);
+	pit->pit_state.flags = 0;
 	for (i = 0; i < 3; i++) {
 		c = &pit->pit_state.channels[i];
 		c->mode = 0xff;