Re: [PATCH 1/1] KVM: Fix potentially recursively get kvm lock

Marcelo Tosatti
2009-05-12T11:55:44Z

On Tue, May 12, 2009 at 05:32:09PM +0800, Sheng Yang wrote:
> kvm_vm_ioctl_deassign_dev_irq() would potentially recursively get kvm->lock,
> because it called kvm_deassigned_irq() which implicit hold kvm->lock by calling
> deassign_host_irq().
>
> Fix it by move kvm_deassign_irq() out of critial region. And add the missing
> lock for deassign_guest_irq().
>
> Reported-by: Alex Williamson <alex.williamson@hp.com>
> Signed-off-by: Sheng Yang <sheng@linux.intel.com>
> ---
> virt/kvm/kvm_main.c | 14 +++++++-------
> 1 files changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 4d00942..3c69655 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -215,6 +215,8 @@ static void kvm_assigned_dev_ack_irq(struct kvm_irq_ack_notifier *kian)
> static void deassign_guest_irq(struct kvm *kvm,
> struct kvm_assigned_dev_kernel *assigned_dev)
> {
> + mutex_lock(&kvm->lock);
> +
> kvm_unregister_irq_ack_notifier(&assigned_dev->ack_notifier);
> assigned_dev->ack_notifier.gsi = -1;
>
> @@ -222,6 +224,8 @@ static void deassign_guest_irq(struct kvm *kvm,
> kvm_free_irq_source_id(kvm, assigned_dev->irq_source_id);
> assigned_dev->irq_source_id = -1;
> assigned_dev->irq_requested_type &= ~(KVM_DEV_IRQ_GUEST_MASK);
> +
> + mutex_unlock(&kvm->lock);
> }
>
> /* The function implicit hold kvm->lock mutex due to cancel_work_sync() */
> @@ -558,20 +562,16 @@ static int kvm_vm_ioctl_deassign_dev_irq(struct kvm *kvm,
> struct kvm_assigned_irq
> *assigned_irq)
> {
> - int r = -ENODEV;
> struct kvm_assigned_dev_kernel *match;
>
> mutex_lock(&kvm->lock);
> -
> match = kvm_find_assigned_dev(&kvm->arch.assigned_dev_head,
> assigned_irq->assigned_dev_id);
> + mutex_unlock(&kvm->lock);

assigned_dev list is protected by kvm->lock. So you could have another
ioctl adding to it at the same time you're searching.

Could either have a separate kvm->assigned_devs_lock, to protect
kvm->arch.assigned_dev_head (users are ioctls that manipulate it), or
change the IRQ injection to use a separate spinlock, kill the workqueue
and call kvm_set_irq from the assigned device interrupt handler.