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>

arch/x86/include/asm/kvm.h

@@ -18,6 +18,7 @@
 #define __KVM_HAVE_GUEST_DEBUG
 #define __KVM_HAVE_MSIX
 #define __KVM_HAVE_MCE
+#define __KVM_HAVE_PIT_STATE2
 
 /* Architectural interrupt line count. */
 #define KVM_NR_INTERRUPTS 256
@@ -237,6 +238,14 @@ struct kvm_pit_state {
 	struct kvm_pit_channel_state channels[3];
 };
 
+#define KVM_PIT_FLAGS_HPET_LEGACY  0x00000001
+
+struct kvm_pit_state2 {
+	struct kvm_pit_channel_state channels[3];
+	__u32 flags;
+	__u32 reserved[9];
+};
+
 struct kvm_reinject_control {
 	__u8 pit_reinject;
 	__u8 reserved[31];