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KVM: Fix racy in kvm_free_assigned_irq

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In the past, kvm_get_kvm() and kvm_put_kvm() was called in assigned device irq
handler and interrupt_work, in order to prevent cancel_work_sync() in
kvm_free_assigned_irq got a illegal state when waiting for interrupt_work done.
But it's tricky and still got two problems:

1. A bug ignored two conditions that cancel_work_sync() would return true result
in a additional kvm_put_kvm().

2. If interrupt type is MSI, we would got a window between cancel_work_sync()
and free_irq(), which interrupt would be injected again...

This patch discard the reference count used for irq handler and interrupt_work,
and ensure the legal state by moving the free function at the very beginning of
kvm_destroy_vm(). And the patch fix the second bug by disable irq before
cancel_work_sync(), which may result in nested disable of irq but OK for we are
going to free it.

Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Sheng Yang 2009-01-06 10:03:03 +08:00 committed by Avi Kivity
parent ad8ba2cd44
commit ba4cef31d5
2 changed files with 20 additions and 9 deletions
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2
arch/x86/kvm/x86.c
View file

@ -4129,11 +4129,11 @@ static void kvm_free_vcpus(struct kvm *kvm)
void kvm_arch_sync_events(struct kvm *kvm)
{
kvm_free_all_assigned_devices(kvm);
}
void kvm_arch_destroy_vm(struct kvm *kvm)
{
kvm_free_all_assigned_devices(kvm);
kvm_iommu_unmap_guest(kvm);
kvm_free_pit(kvm);
kfree(kvm->arch.vpic);

27
virt/kvm/kvm_main.c
View file

@ -173,7 +173,6 @@ static void kvm_assigned_dev_interrupt_work_handler(struct work_struct *work)
assigned_dev->host_irq_disabled = false;
}
mutex_unlock(&assigned_dev->kvm->lock);
kvm_put_kvm(assigned_dev->kvm);
}
static irqreturn_t kvm_assigned_dev_intr(int irq, void *dev_id)
@ -181,8 +180,6 @@ static irqreturn_t kvm_assigned_dev_intr(int irq, void *dev_id)
struct kvm_assigned_dev_kernel *assigned_dev =
(struct kvm_assigned_dev_kernel *) dev_id;
kvm_get_kvm(assigned_dev->kvm);
schedule_work(&assigned_dev->interrupt_work);
disable_irq_nosync(irq);
@ -213,6 +210,7 @@ static void kvm_assigned_dev_ack_irq(struct kvm_irq_ack_notifier *kian)
}
}
/* The function implicit hold kvm->lock mutex due to cancel_work_sync() */
static void kvm_free_assigned_irq(struct kvm *kvm,
struct kvm_assigned_dev_kernel *assigned_dev)
{
@ -228,11 +226,24 @@ static void kvm_free_assigned_irq(struct kvm *kvm,
if (!assigned_dev->irq_requested_type)
return;
if (cancel_work_sync(&assigned_dev->interrupt_work))
/* We had pending work. That means we will have to take
* care of kvm_put_kvm.
*/
kvm_put_kvm(kvm);
/*
* In kvm_free_device_irq, cancel_work_sync return true if:
* 1. work is scheduled, and then cancelled.
* 2. work callback is executed.
*
* The first one ensured that the irq is disabled and no more events
* would happen. But for the second one, the irq may be enabled (e.g.
* for MSI). So we disable irq here to prevent further events.
*
* Notice this maybe result in nested disable if the interrupt type is
* INTx, but it's OK for we are going to free it.
*
* If this function is a part of VM destroy, please ensure that till
* now, the kvm state is still legal for probably we also have to wait
* interrupt_work done.
*/
disable_irq_nosync(assigned_dev->host_irq);
cancel_work_sync(&assigned_dev->interrupt_work);
free_irq(assigned_dev->host_irq, (void *)assigned_dev);