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vfio: Fix virqfd release race

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vfoi-pci supports a mechanism like KVM's irqfd for unmasking an
interrupt through an eventfd.  There are two ways to shutdown this
interface: 1) close the eventfd, 2) ioctl (such as disabling the
interrupt).  Both of these do the release through a workqueue,
which can result in a segfault if two jobs get queued for the same
virqfd.

Fix this by protecting the pointer to these virqfds by a spinlock.
The vfio pci device will therefore no longer have a reference to it
once the release job is queued under lock.  On the ioctl side, we
still flush the workqueue to ensure that any outstanding releases
are completed.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
This commit is contained in:
Alex Williamson 2012-09-21 10:48:28 -06:00
parent b37b593e20
commit b68e7fa879
1 changed files with 56 additions and 20 deletions
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76
drivers/vfio/pci/vfio_pci_intrs.c
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@ -76,9 +76,24 @@ static int virqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
schedule_work(&virqfd->inject);
}
if (flags & POLLHUP)
/* The eventfd is closing, detach from VFIO */
virqfd_deactivate(virqfd);
if (flags & POLLHUP) {
unsigned long flags;
spin_lock_irqsave(&virqfd->vdev->irqlock, flags);
/*
* The eventfd is closing, if the virqfd has not yet been
* queued for release, as determined by testing whether the
* vdev pointer to it is still valid, queue it now. As
* with kvm irqfds, we know we won't race against the virqfd
* going away because we hold wqh->lock to get here.
*/
if (*(virqfd->pvirqfd) == virqfd) {
*(virqfd->pvirqfd) = NULL;
virqfd_deactivate(virqfd);
}
spin_unlock_irqrestore(&virqfd->vdev->irqlock, flags);
}
return 0;
}
@ -93,7 +108,6 @@ static void virqfd_ptable_queue_proc(struct file *file,
static void virqfd_shutdown(struct work_struct *work)
{
struct virqfd *virqfd = container_of(work, struct virqfd, shutdown);
struct virqfd **pvirqfd = virqfd->pvirqfd;
u64 cnt;
eventfd_ctx_remove_wait_queue(virqfd->eventfd, &virqfd->wait, &cnt);
@ -101,7 +115,6 @@ static void virqfd_shutdown(struct work_struct *work)
eventfd_ctx_put(virqfd->eventfd);
kfree(virqfd);
*pvirqfd = NULL;
}
static void virqfd_inject(struct work_struct *work)
@ -122,15 +135,11 @@ static int virqfd_enable(struct vfio_pci_device *vdev,
int ret = 0;
unsigned int events;
if (*pvirqfd)
return -EBUSY;
virqfd = kzalloc(sizeof(*virqfd), GFP_KERNEL);
if (!virqfd)
return -ENOMEM;
virqfd->pvirqfd = pvirqfd;
*pvirqfd = virqfd;
virqfd->vdev = vdev;
virqfd->handler = handler;
virqfd->thread = thread;
@ -153,6 +162,23 @@ static int virqfd_enable(struct vfio_pci_device *vdev,
virqfd->eventfd = ctx;
/*
* virqfds can be released by closing the eventfd or directly
* through ioctl. These are both done through a workqueue, so
* we update the pointer to the virqfd under lock to avoid
* pushing multiple jobs to release the same virqfd.
*/
spin_lock_irq(&vdev->irqlock);
if (*pvirqfd) {
spin_unlock_irq(&vdev->irqlock);
ret = -EBUSY;
goto fail;
}
*pvirqfd = virqfd;
spin_unlock_irq(&vdev->irqlock);
/*
* Install our own custom wake-up handling so we are notified via
* a callback whenever someone signals the underlying eventfd.
@ -187,19 +213,29 @@ fail:
fput(file);
kfree(virqfd);
*pvirqfd = NULL;
return ret;
}
static void virqfd_disable(struct virqfd *virqfd)
static void virqfd_disable(struct vfio_pci_device *vdev,
struct virqfd **pvirqfd)
{
if (!virqfd)
return;
unsigned long flags;
virqfd_deactivate(virqfd);
spin_lock_irqsave(&vdev->irqlock, flags);
/* Block until we know all outstanding shutdown jobs have completed. */
if (*pvirqfd) {
virqfd_deactivate(*pvirqfd);
*pvirqfd = NULL;
}
spin_unlock_irqrestore(&vdev->irqlock, flags);
/*
* Block until we know all outstanding shutdown jobs have completed.
* Even if we don't queue the job, flush the wq to be sure it's
* been released.
*/
flush_workqueue(vfio_irqfd_cleanup_wq);
}
@ -392,8 +428,8 @@ static int vfio_intx_set_signal(struct vfio_pci_device *vdev, int fd)
static void vfio_intx_disable(struct vfio_pci_device *vdev)
{
vfio_intx_set_signal(vdev, -1);
virqfd_disable(vdev->ctx[0].unmask);
virqfd_disable(vdev->ctx[0].mask);
virqfd_disable(vdev, &vdev->ctx[0].unmask);
virqfd_disable(vdev, &vdev->ctx[0].mask);
vdev->irq_type = VFIO_PCI_NUM_IRQS;
vdev->num_ctx = 0;
kfree(vdev->ctx);
@ -539,8 +575,8 @@ static void vfio_msi_disable(struct vfio_pci_device *vdev, bool msix)
vfio_msi_set_block(vdev, 0, vdev->num_ctx, NULL, msix);
for (i = 0; i < vdev->num_ctx; i++) {
virqfd_disable(vdev->ctx[i].unmask);
virqfd_disable(vdev->ctx[i].mask);
virqfd_disable(vdev, &vdev->ctx[i].unmask);
virqfd_disable(vdev, &vdev->ctx[i].mask);
}
if (msix) {
@ -577,7 +613,7 @@ static int vfio_pci_set_intx_unmask(struct vfio_pci_device *vdev,
vfio_send_intx_eventfd, NULL,
&vdev->ctx[0].unmask, fd);
virqfd_disable(vdev->ctx[0].unmask);
virqfd_disable(vdev, &vdev->ctx[0].unmask);
}
return 0;