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Date: Fri, 21 Sep 2012 10:55:06 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: alex.williamson@...hat.com
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] vfio: Fix virqfd release race
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@...hat.com>
---
drivers/vfio/pci/vfio_pci_intrs.c | 76 +++++++++++++++++++++++++++----------
1 file changed, 56 insertions(+), 20 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
index 211a492..d8dedc7 100644
--- a/drivers/vfio/pci/vfio_pci_intrs.c
+++ b/drivers/vfio/pci/vfio_pci_intrs.c
@@ -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;
@@ -154,6 +163,23 @@ 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;
+
+ spin_lock_irqsave(&vdev->irqlock, flags);
+
+ if (*pvirqfd) {
+ virqfd_deactivate(*pvirqfd);
+ *pvirqfd = NULL;
+ }
- virqfd_deactivate(virqfd);
+ spin_unlock_irqrestore(&vdev->irqlock, flags);
- /* Block until we know all outstanding shutdown jobs have completed. */
+ /*
+ * 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;
--
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