Linux Virtualization - Sep 2012 - [PATCH 0/2] virtio-mmio updates for 3.7

Hi Rusty,

Would you be so kind and consider getting those two small fixes into
3.7 merge? All credits go to Brian, all shame on me :-)

Cheers!

Pawel

Brian Foley (2):
  virtio_mmio: fix off by one error allocating queue
  virtio_mmio: Don't attempt to create empty virtqueues

 drivers/virtio/virtio_mmio.c |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

-- 
1.7.9.5

From: Brian Foley <brian.foley at arm.com>

vm_setup_vq fails to allow VirtQueues needing only 2 pages of
storage, as it should. Found with a kernel using 64kB pages, but
can be provoked if a virtio device reports QueueNumMax where the
descriptor table and available ring fit in one page, and the used
ring on the second (<= 227 descriptors with 4kB pages and <= 3640
with 64kB pages.)

Signed-off-by: Brian Foley <brian.foley at arm.com>
Signed-off-by: Pawel Moll <pawel.moll at arm.com>
---
 drivers/virtio/virtio_mmio.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 453db0c..58e2d78 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -335,8 +335,8 @@ static struct virtqueue *vm_setup_vq(struct virtio_device
*vdev, unsigned index,
 	while (1) {
 		size = PAGE_ALIGN(vring_size(info->num,
 				VIRTIO_MMIO_VRING_ALIGN));
-		/* Already smallest possible allocation? */
-		if (size <= VIRTIO_MMIO_VRING_ALIGN * 2) {
+		/* Did the last iter shrink the queue below minimum size? */
+		if (size < VIRTIO_MMIO_VRING_ALIGN * 2) {
 			err = -ENOMEM;
 			goto error_alloc_pages;
 		}
-- 
1.7.9.5

From: Brian Foley <brian.foley at arm.com>

If a virtio device reports a QueueNumMax of 0, vring_new_virtqueue()
doesn't check this, and thanks to an unsigned (i < num - 1) loop
guard, scribbles over memory when initialising the free list.

Avoid by not trying to create zero-descriptor queues, as there's no
way to do any I/O with one.

Signed-off-by: Brian Foley <brian.foley at arm.com>
Signed-off-by: Pawel Moll <pawel.moll at arm.com>
---
 drivers/virtio/virtio_mmio.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 58e2d78..6979c1b 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -332,6 +332,16 @@ static struct virtqueue *vm_setup_vq(struct virtio_device
*vdev, unsigned index,
 	 * and two rings (which makes it "alignment_size * 2")
 	 */
 	info->num = readl(vm_dev->base + VIRTIO_MMIO_QUEUE_NUM_MAX);
+
+	/* If the device reports a 0 entry queue, we won't be able to
+	 * use it to perform I/O, and vring_new_virtqueue() can't create
+	 * empty queues anyway, so don't bother to set up the device.
+	 */
+	if (info->num == 0) {
+		err = -ENOENT;
+		goto error_alloc_pages;
+	}
+
 	while (1) {
 		size = PAGE_ALIGN(vring_size(info->num,
 				VIRTIO_MMIO_VRING_ALIGN));
-- 
1.7.9.5

Pawel Moll <pawel.moll at arm.com> writes:
> Hi Rusty,
>
> Would you be so kind and consider getting those two small fixes into
> 3.7 merge? All credits go to Brian, all shame on me :-)
Should these also be cc'd to stable at kernel.org?

Cheers,
Rusty.