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Subject[PATCH 34/40] KVM: PIT: provide an option to disable interrupt reinjection
Date
From: Marcelo Tosatti <mtosatti@redhat.com>

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>
---
arch/x86/include/asm/kvm.h | 5 +++++
arch/x86/kvm/i8254.c | 4 ++++
arch/x86/kvm/i8254.h | 1 +
arch/x86/kvm/x86.c | 21 +++++++++++++++++++++
include/linux/kvm.h | 4 ++++
5 files changed, 35 insertions(+), 0 deletions(-)
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_guest_debug_arch {
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 @@ static int __pit_timer_fn(struct kvm_kpit_state *ps)
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 kvm *kvm)
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 @@ struct kvm_kpit_timer {
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 @@ int kvm_dev_ioctl_check_extension(long ext)
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 @@ static int kvm_vm_ioctl_set_pit(struct kvm *kvm, struct kvm_pit_state *ps)
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 @@ long kvm_arch_vm_ioctl(struct file *filp,
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 11e3e61..ae7a12c 100644
--- a/include/linux/kvm.h
+++ b/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_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_REINJECT_CONTROL _IO(KVMIO, 0x71)

/*
* ioctls for vcpu fds
--
1.6.0.6


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