Commit ba4cef31 authored by Sheng Yang's avatar Sheng Yang Committed by Avi Kivity
Browse files

KVM: Fix racy in kvm_free_assigned_irq 



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: default avatarSheng Yang <sheng@linux.intel.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent ad8ba2cd

arch/x86/kvm/x86.c

+1 −1
Original line number Diff line number Diff line
@@ -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);

virt/kvm/kvm_main.c

+19 −8
Original line number Diff line number Diff line
@@ -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.

	/*

	 * 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.

	 */

		kvm_put_kvm(kvm);

	disable_irq_nosync(assigned_dev->host_irq);

	cancel_work_sync(&assigned_dev->interrupt_work);



	free_irq(assigned_dev->host_irq, (void *)assigned_dev);

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