[patch 2/2] KVM: PIT: provide an option to disable interrupt reinjection

[Marcelo Tosatti <mtosatti@redhat.com>]

[-- Attachment #1: i8254-disable-reinject --]
[-- Type: text/plain, Size: 3516 bytes --]

Certain clocks (such as TSC) in older 2.6 guests overaccount for lost
ticks, causing severe time drift. Interrupt reinjection magnifies the
problem.

Provide an option to disable it.

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

Index: kvm/arch/x86/kvm/i8254.c
===================================================================
--- kvm.orig/arch/x86/kvm/i8254.c
+++ kvm/arch/x86/kvm/i8254.c
@@ -201,6 +201,9 @@ static int __pit_timer_fn(struct kvm_kpi
 	if (!atomic_inc_and_test(&pt->pending))
 		set_bit(KVM_REQ_PENDING_TIMER, &vcpu0->requests);
 
+	if (!pt->reinject)
+		atomic_set(&pt->pending, 1);
+
 	if (vcpu0 && waitqueue_active(&vcpu0->wq))
 		wake_up_interruptible(&vcpu0->wq);
 
@@ -580,6 +583,7 @@ struct kvm_pit *kvm_create_pit(struct kv
 	pit_state->irq_ack_notifier.gsi = 0;
 	pit_state->irq_ack_notifier.irq_acked = kvm_pit_ack_irq;
 	kvm_register_irq_ack_notifier(kvm, &pit_state->irq_ack_notifier);
+	pit_state->pit_timer.reinject = true;
 	mutex_unlock(&pit->pit_state.lock);
 
 	kvm_pit_reset(pit);
Index: kvm/arch/x86/kvm/i8254.h
===================================================================
--- kvm.orig/arch/x86/kvm/i8254.h
+++ kvm/arch/x86/kvm/i8254.h
@@ -9,6 +9,7 @@ struct kvm_kpit_timer {
 	s64 period; /* unit: ns */
 	s64 scheduled;
 	atomic_t pending;
+	bool reinject;
 };
 
 struct kvm_kpit_channel_state {
Index: kvm/arch/x86/kvm/x86.c
===================================================================
--- kvm.orig/arch/x86/kvm/x86.c
+++ kvm/arch/x86/kvm/x86.c
@@ -991,6 +991,7 @@ int kvm_dev_ioctl_check_extension(long e
 	case KVM_CAP_NOP_IO_DELAY:
 	case KVM_CAP_MP_STATE:
 	case KVM_CAP_SYNC_MMU:
+	case KVM_CAP_PIT_REINJECT_CONTROL:
 		r = 1;
 		break;
 	case KVM_CAP_COALESCED_MMIO:
@@ -1723,6 +1724,13 @@ static int kvm_vm_ioctl_set_pit(struct k
 	return r;
 }
 
+static int kvm_vm_ioctl_pit_reinject(struct kvm *kvm,
+				     struct kvm_pit_reinject_control *control)
+{
+	kvm->arch.vpit->pit_state.pit_timer.reinject = control->reinject;
+	return 0;
+}
+
 /*
  * Get (and clear) the dirty memory log for a memory slot.
  */
@@ -1920,6 +1928,20 @@ long kvm_arch_vm_ioctl(struct file *filp
 		r = 0;
 		break;
 	}
+	case KVM_PIT_REINJECT_CONTROL: {
+		struct kvm_pit_reinject_control control;
+		r =  -EFAULT;
+		if (copy_from_user(&control, argp, sizeof(control)))
+			goto out;
+		r = -ENXIO;
+		if (!kvm->arch.vpit)
+			goto out;
+		r = kvm_vm_ioctl_pit_reinject(kvm, &control);
+		if (r)
+			goto out;
+		r = 0;
+		break;
+	}
 	default:
 		;
 	}
Index: kvm/include/linux/kvm.h
===================================================================
--- kvm.orig/include/linux/kvm.h
+++ kvm/include/linux/kvm.h
@@ -396,6 +396,9 @@ struct kvm_trace_rec {
 #if defined(CONFIG_X86)
 #define KVM_CAP_SET_GUEST_DEBUG 23
 #endif
+#if defined(CONFIG_X86)
+#define KVM_CAP_PIT_REINJECT_CONTROL 24
+#endif
 
 /*
  * ioctls for VM fds
@@ -429,6 +432,7 @@ struct kvm_trace_rec {
 				   struct kvm_assigned_pci_dev)
 #define KVM_ASSIGN_IRQ _IOR(KVMIO, 0x70, \
 			    struct kvm_assigned_irq)
+#define KVM_PIT_REINJECT_CONTROL  _IO(KVMIO, 0x71)
 
 /*
  * ioctls for vcpu fds
Index: kvm/arch/x86/include/asm/kvm.h
===================================================================
--- kvm.orig/arch/x86/include/asm/kvm.h
+++ kvm/arch/x86/include/asm/kvm.h
@@ -226,4 +226,8 @@ struct kvm_guest_debug_arch {
 struct kvm_pit_state {
 	struct kvm_pit_channel_state channels[3];
 };
+
+struct kvm_pit_reinject_control {
+	__u8 reinject;
+};
 #endif /* _ASM_X86_KVM_H */

--