[PATCH] virtio_ring: return an error pointer from vring_create_virtqueue()
Michael S. Tsirkin
mst at redhat.com
Thu Nov 5 11:43:46 PST 2026
On Thu, Nov 05, 2026 at 08:34:25PM +0100, Stjepan Poljak wrote:
> vring_create_virtqueue() and vring_create_virtqueue_map() return NULL
> on any failure, so the error returned from vring_alloc_queue_split()
> is lost and turned into -ENOMEM. This is especially misleading if
> vring_alloc_queue_split() rejects a queue size with -EINVAL (i.e. if
> queue size is not a power of two):
>
> virtio_blk virtio0: Bad virtqueue length 100
> virtio_blk virtio0: probe with driver virtio_blk failed with error -12
>
> So the error points whoever debugs it at an allocation failure that
> never happened.
>
> Return an ERR_PTR() instead: the error from vring_alloc_queue_split()
> or vring_alloc_queue_packed(), or -ENOMEM when allocating the
> virtqueue itself fails. Make the callers, virtio_pci (modern and
> legacy), virtio_mmio, virtio_vdpa, virtio_ccw and virtio_uml, check
> with IS_ERR() and pass the error on. The error path in virtio_ccw
> deletes a non-NULL vq, so clear vq there before taking it.
>
> Co-Authored-By: Claude Opus 5.5 <noreply at anthropic.com>
not how you ae supposed to attribute LLM use.
> Signed-off-by: Stjepan Poljak <stjepan.poljak at gmail.com>
> ---
> Tested on x86_64 with a virtio-mmio virtio-blk device offering a
> 100-entry queue: the probe now fails with -22 instead of -12, and a
> 128-entry queue probes as before. The other transports are only
> compile-tested (x86_64, ARCH=um, s390 with clang, W=1).
>
> No Fixes: tag, since the error has been -ENOMEM since 2010 and nothing
> regressed.
>
> This conflicts trivially with patch 07/12 of Alexander Graf's "virtio:
> support devices that own their virtqueue memory" v2:
> https://lore.kernel.org/virtualization/20260818211425.91009-1-graf@amazon.com/
> ---
> arch/um/drivers/virtio_uml.c | 4 ++--
> drivers/s390/virtio/virtio_ccw.c | 5 +++--
> drivers/virtio/virtio_mmio.c | 4 ++--
> drivers/virtio/virtio_pci_legacy.c | 4 ++--
> drivers/virtio/virtio_pci_modern.c | 4 ++--
> drivers/virtio/virtio_ring.c | 12 +++++++-----
> drivers/virtio/virtio_vdpa.c | 4 ++--
> include/linux/virtio_ring.h | 6 +++++-
> 8 files changed, 25 insertions(+), 18 deletions(-)
>
> diff --git a/arch/um/drivers/virtio_uml.c b/arch/um/drivers/virtio_uml.c
> index 881c34098a74..8b645523277f 100644
> --- a/arch/um/drivers/virtio_uml.c
> +++ b/arch/um/drivers/virtio_uml.c
> @@ -984,8 +984,8 @@ static struct virtqueue *vu_setup_vq(struct virtio_device *vdev,
>
> vq = vring_create_virtqueue(index, num, PAGE_SIZE, vdev, true, true,
> ctx, vu_notify, callback, info->name);
> - if (!vq) {
> - rc = -ENOMEM;
> + if (IS_ERR(vq)) {
> + rc = PTR_ERR(vq);
> goto error_create;
> }
> vq->priv = info;
> diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> index 552d77998012..c5a30f0a2bc2 100644
> --- a/drivers/s390/virtio/virtio_ccw.c
> +++ b/drivers/s390/virtio/virtio_ccw.c
> @@ -590,10 +590,11 @@ static struct virtqueue *virtio_ccw_setup_vq(struct virtio_device *vdev,
> vdev, true, may_reduce, ctx,
> notify, callback, name);
>
> - if (!vq) {
> + if (IS_ERR(vq)) {
> /* For now, we fail if we can't get the requested size. */
> dev_warn(&vcdev->cdev->dev, "no vq\n");
> - err = -ENOMEM;
> + err = PTR_ERR(vq);
> + vq = NULL;
> goto out_err;
> }
>
> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> index e2ec0ec01d67..c403a025006e 100644
> --- a/drivers/virtio/virtio_mmio.c
> +++ b/drivers/virtio/virtio_mmio.c
> @@ -396,8 +396,8 @@ static struct virtqueue *vm_setup_vq(struct virtio_device *vdev, unsigned int in
> /* Create the vring */
> vq = vring_create_virtqueue(index, num, VIRTIO_MMIO_VRING_ALIGN, vdev,
> true, true, ctx, notify, callback, name);
> - if (!vq) {
> - err = -ENOMEM;
> + if (IS_ERR(vq)) {
> + err = PTR_ERR(vq);
> goto error_new_virtqueue;
> }
>
> diff --git a/drivers/virtio/virtio_pci_legacy.c b/drivers/virtio/virtio_pci_legacy.c
> index 8115aa39e01e..9d94fffff344 100644
> --- a/drivers/virtio/virtio_pci_legacy.c
> +++ b/drivers/virtio/virtio_pci_legacy.c
> @@ -130,8 +130,8 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
> VIRTIO_PCI_VRING_ALIGN, &vp_dev->vdev,
> true, false, ctx,
> vp_notify, callback, name);
> - if (!vq)
> - return ERR_PTR(-ENOMEM);
> + if (IS_ERR(vq))
> + return vq;
>
> vq->num_max = num;
>
> diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
> index 922e2df027de..28ccb2130e27 100644
> --- a/drivers/virtio/virtio_pci_modern.c
> +++ b/drivers/virtio/virtio_pci_modern.c
> @@ -720,8 +720,8 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
> SMP_CACHE_BYTES, &vp_dev->vdev,
> true, true, ctx,
> notify, callback, name);
> - if (!vq)
> - return ERR_PTR(-ENOMEM);
> + if (IS_ERR(vq))
> + return vq;
>
> vq->num_max = num;
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index f683a2d6a200..6dd4a7651bde 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -1421,13 +1421,13 @@ static struct virtqueue *vring_create_virtqueue_split(
> err = vring_alloc_queue_split(&vring_split, vdev, num, vring_align,
> may_reduce_num, map);
> if (err)
> - return NULL;
> + return ERR_PTR(err);
>
> vq = __vring_new_virtqueue_split(index, &vring_split, vdev, weak_barriers,
> context, notify, callback, name, map);
> if (!vq) {
> vring_free_split(&vring_split, vdev, map);
> - return NULL;
> + return ERR_PTR(-ENOMEM);
> }
>
> to_vvq(vq)->we_own_ring = true;
> @@ -2671,15 +2671,17 @@ static struct virtqueue *vring_create_virtqueue_packed(
> {
> struct vring_virtqueue_packed vring_packed = {};
> struct virtqueue *vq;
> + int err;
>
> - if (vring_alloc_queue_packed(&vring_packed, vdev, num, map))
> - return NULL;
> + err = vring_alloc_queue_packed(&vring_packed, vdev, num, map);
> + if (err)
> + return ERR_PTR(err);
>
> vq = __vring_new_virtqueue_packed(index, &vring_packed, vdev, weak_barriers,
> context, notify, callback, name, map);
> if (!vq) {
> vring_free_packed(&vring_packed, vdev, map);
> - return NULL;
> + return ERR_PTR(-ENOMEM);
> }
>
> to_vvq(vq)->we_own_ring = true;
> diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
> index f9559b6b2e0b..c1b6134b2267 100644
> --- a/drivers/virtio/virtio_vdpa.c
> +++ b/drivers/virtio/virtio_vdpa.c
> @@ -208,8 +208,8 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
> vq = vring_create_virtqueue_map(index, max_num, align, vdev,
> true, may_reduce_num, ctx,
> notify, callback, name, map);
> - if (!vq) {
> - err = -ENOMEM;
> + if (IS_ERR(vq)) {
> + err = PTR_ERR(vq);
> goto error_new_virtqueue;
> }
>
> diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
> index c97a12c1cda3..c808ca7e8d58 100644
> --- a/include/linux/virtio_ring.h
> +++ b/include/linux/virtio_ring.h
> @@ -66,6 +66,9 @@ struct device;
> * may_reduce_num is set, then this may allocate a smaller ring than
> * expected. The caller should query virtqueue_get_vring_size to learn
> * the actual size of the ring.
> + *
> + * Returns the virtqueue or an ERR_PTR() on failure: -EINVAL if num is
> + * not a valid ring size, -ENOMEM if the ring could not be allocated.
> */
> struct virtqueue *vring_create_virtqueue(unsigned int index,
> unsigned int num,
> @@ -80,7 +83,8 @@ struct virtqueue *vring_create_virtqueue(unsigned int index,
>
> /*
> * Creates a virtqueue and allocates the descriptor ring with per
> - * virtqueue mapping operations.
> + * virtqueue mapping operations. Returns the virtqueue or an ERR_PTR()
> + * on failure, like vring_create_virtqueue().
> */
> struct virtqueue *vring_create_virtqueue_map(unsigned int index,
> unsigned int num,
>
> base-commit: 1a577f9402c1780cc1e663f48d5dd54c02051b09
> --
> 2.53.0
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