KVM: PIT: provide an option to disable interrupt reinjection
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.
[avi: allow room for expansion in case we want to disable reinjection
of other timers]
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/include/asm/kvm.h b/arch/x86/include/asm/kvm.h
index 32eb96c..54bcf22 100644
--- a/arch/x86/include/asm/kvm.h
+++ b/arch/x86/include/asm/kvm.h
@@ -233,4 +233,9 @@
struct kvm_pit_state {
struct kvm_pit_channel_state channels[3];
};
+
+struct kvm_reinject_control {
+ __u8 pit_reinject;
+ __u8 reserved[31];
+};
#endif /* _ASM_X86_KVM_H */
diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 72bd275..528daad 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -201,6 +201,9 @@
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 @@
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);
diff --git a/arch/x86/kvm/i8254.h b/arch/x86/kvm/i8254.h
index 4178022..76959c4 100644
--- a/arch/x86/kvm/i8254.h
+++ b/arch/x86/kvm/i8254.h
@@ -9,6 +9,7 @@
s64 period; /* unit: ns */
s64 scheduled;
atomic_t pending;
+ bool reinject;
};
struct kvm_kpit_channel_state {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c3fbe8c..a1f1461 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -993,6 +993,7 @@
case KVM_CAP_NOP_IO_DELAY:
case KVM_CAP_MP_STATE:
case KVM_CAP_SYNC_MMU:
+ case KVM_CAP_REINJECT_CONTROL:
r = 1;
break;
case KVM_CAP_COALESCED_MMIO:
@@ -1728,6 +1729,15 @@
return r;
}
+static int kvm_vm_ioctl_reinject(struct kvm *kvm,
+ struct kvm_reinject_control *control)
+{
+ if (!kvm->arch.vpit)
+ return -ENXIO;
+ kvm->arch.vpit->pit_state.pit_timer.reinject = control->pit_reinject;
+ return 0;
+}
+
/*
* Get (and clear) the dirty memory log for a memory slot.
*/
@@ -1925,6 +1935,17 @@
r = 0;
break;
}
+ case KVM_REINJECT_CONTROL: {
+ struct kvm_reinject_control control;
+ r = -EFAULT;
+ if (copy_from_user(&control, argp, sizeof(control)))
+ goto out;
+ r = kvm_vm_ioctl_reinject(kvm, &control);
+ if (r)
+ goto out;
+ r = 0;
+ break;
+ }
default:
;
}
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 11e3e619..ae7a12c 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -396,6 +396,9 @@
#if defined(CONFIG_X86)
#define KVM_CAP_SET_GUEST_DEBUG 23
#endif
+#if defined(CONFIG_X86)
+#define KVM_CAP_REINJECT_CONTROL 24
+#endif
/*
* ioctls for VM fds
@@ -429,6 +432,7 @@
struct kvm_assigned_pci_dev)
#define KVM_ASSIGN_IRQ _IOR(KVMIO, 0x70, \
struct kvm_assigned_irq)
+#define KVM_REINJECT_CONTROL _IO(KVMIO, 0x71)
/*
* ioctls for vcpu fds