In virtblk_add_req(), each request consumes 2 extra descriptors (out_hdr and in_hdr) in addition to the data scatter-gather segments. When a hypervisor (e.g. QNX Hypervisor) advertises VIRTIO_BLK_F_SEG_MAX with seg_max = 1024 alongside a 1024-entry split ring (vring.num = 1024) and VIRTIO_RING_F_INDIRECT_DESC disabled, lim->max_segments is set to 1024. When the block layer submits requests with 1023 or 1024 data segments, total_sg reaches 1025 or 1026. This exceeds vring.num (1024), causing virtqueue_add_split() to return -ENOSPC and permanently wedge the blk-mq queue. Furthermore, the Virtio specification (2.7.5.3.1) requires that a descriptor chain never exceed the Queue Size, and virtqueue_add_split() falls back to direct descriptors if indirect table allocation fails. Fix this by: 1. Rejecting queues with ring_size < 3 at probe, or ring_size < (queue_max_segments + 2) during resume/reset recovery in init_vq(). 2. Unconditionally clamping sg_elems to (ring_size - 2) across all virtqueues in virtblk_read_limits(). Fixes: 0864b79a1533 ("virtio: block: dynamic maximum segments") Signed-off-by: Sergii Ushakov --- Changes in v4: - Add Fixes tag. - Add code comments in init_vq() documenting the constants 3 and + 2. drivers/block/virtio_blk.c | 44 +++++++++++++++++++++++++++++++++++++- 1 file changed, 43 insertions(+), 1 deletion(-) diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c index 32bf3ba07a9d..cafca309b4d0 100644 --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -1021,6 +1021,30 @@ static int init_vq(struct virtio_blk *vblk) goto out; for (i = 0; i < num_vqs; i++) { + unsigned int ring_size = virtqueue_get_vring_size(vqs[i]); + /* + * Each request consumes 2 extra descriptors (out_hdr and + * in_hdr) in addition to the data segments. + * + * At initial probe (!vblk->disk), each virtqueue must fit at + * least 1 data segment + 2 header descriptors (3). + * On resume/recovery (vblk->disk), each virtqueue must fit the + * existing queue_max_segments() + 2 header descriptors. + */ + unsigned int min_ring_size = 3; + + if (vblk->disk) + min_ring_size = queue_max_segments(vblk->disk->queue) + 2; + + if (ring_size < min_ring_size) { + dev_err(&vdev->dev, + "virtqueue %u ring size %u is smaller than minimum %u\n", + i, ring_size, min_ring_size); + vdev->config->del_vqs(vdev); + err = -EINVAL; + goto out; + } + spin_lock_init(&vblk->vqs[i].lock); vblk->vqs[i].vq = vqs[i]; } @@ -1253,7 +1277,7 @@ static int virtblk_read_limits(struct virtio_blk *vblk, u16 min_io_size; u8 physical_block_exp, alignment_offset; size_t max_dma_size; - int err; + int err, i; /* We need to know how many segments before we allocate. */ err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SEG_MAX, @@ -1267,6 +1291,23 @@ static int virtblk_read_limits(struct virtio_blk *vblk, /* Prevent integer overflows and honor max vq size */ sg_elems = min_t(u32, sg_elems, VIRTIO_BLK_MAX_SG_ELEMS - 2); + /* + * virtblk_add_req() uses separate outgoing and incoming header + * descriptors (out_hdr and in_hdr), consuming 2 extra descriptors + * per request in addition to the data segments. + * + * Per virtio specification (2.7.5.3.1), a driver MUST NOT create a + * descriptor chain longer than the Queue Size of the device. + * + * Clamp max_segments to (ring_size - 2) across all virtqueues so + * that a request never exceeds the ring size of any queue. + */ + for (i = 0; i < vblk->num_vqs; i++) { + u32 ring_size = virtqueue_get_vring_size(vblk->vqs[i].vq); + + sg_elems = min_t(u32, sg_elems, ring_size - 2); + } + /* We can handle whatever the host told us to handle. */ lim->max_segments = sg_elems; @@ -1466,6 +1507,7 @@ static int virtblk_probe(struct virtio_device *vdev) mutex_init(&vblk->vdev_mutex); vblk->vdev = vdev; + vblk->disk = NULL; INIT_WORK(&vblk->config_work, virtblk_config_changed_work); -- 2.55.0.1082.g2b9226bbc0-goog