On Wed, Jul 10, 2024 at 4:43 AM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> virtio balloon communicates to the core that in some
> configurations vq #s are non-contiguous by setting name
> pointer to NULL.
>
> Unfortunately, core then turned around and just made them
> contiguous again. Result is that driver is out of spec.
Thanks for fixing this - I think the overall approach of the patch looks good.
> Implement what the API was supposed to do
> in the 1st place. Compatibility with buggy hypervisors
> is handled inside virtio-balloon, which is the only driver
> making use of this facility, so far.
In addition to virtio-balloon, I believe the same problem also affects
the virtio-fs device, since queue 1 is only supposed to be present if
VIRTIO_FS_F_NOTIFICATION is negotiated, and the request queues are
meant to be queue indexes 2 and up. From a look at the Linux driver
(virtio_fs.c), it appears like it never acks VIRTIO_FS_F_NOTIFICATION
and assumes that request queues start at index 1 rather than 2, which
looks out of spec to me, but the current device implementations (that
I am aware of, anyway) are also broken in the same way, so it ends up
working today. Queue numbering in a spec-compliant device and the
current Linux driver would mismatch; what the driver considers to be
the first request queue (index 1) would be ignored by the device since
queue index 1 has no function if F_NOTIFICATION isn't negotiated.
[...]
> diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
> index 7d82facafd75..fa606e7321ad 100644
> --- a/drivers/virtio/virtio_pci_common.c
> +++ b/drivers/virtio/virtio_pci_common.c
> @@ -293,7 +293,7 @@ static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned int nvqs,
> struct virtio_pci_device *vp_dev = to_vp_device(vdev);
> struct virtqueue_info *vqi;
> u16 msix_vec;
> - int i, err, nvectors, allocated_vectors, queue_idx = 0;
> + int i, err, nvectors, allocated_vectors;
>
> vp_dev->vqs = kcalloc(nvqs, sizeof(*vp_dev->vqs), GFP_KERNEL);
> if (!vp_dev->vqs)
> @@ -332,7 +332,7 @@ static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned int nvqs,
> msix_vec = allocated_vectors++;
> else
> msix_vec = VP_MSIX_VQ_VECTOR;
> - vqs[i] = vp_setup_vq(vdev, queue_idx++, vqi->callback,
> + vqs[i] = vp_setup_vq(vdev, i, vqi->callback,
> vqi->name, vqi->ctx, msix_vec);
> if (IS_ERR(vqs[i])) {
> err = PTR_ERR(vqs[i]);
> @@ -368,7 +368,7 @@ static int vp_find_vqs_intx(struct virtio_device *vdev, unsigned int nvqs,
> struct virtqueue_info vqs_info[])
> {
> struct virtio_pci_device *vp_dev = to_vp_device(vdev);
> - int i, err, queue_idx = 0;
> + int i, err;
>
> vp_dev->vqs = kcalloc(nvqs, sizeof(*vp_dev->vqs), GFP_KERNEL);
> if (!vp_dev->vqs)
> @@ -388,8 +388,13 @@ static int vp_find_vqs_intx(struct virtio_device *vdev, unsigned int nvqs,
> vqs[i] = NULL;
> continue;
> }
> +<<<<<<< HEAD
> vqs[i] = vp_setup_vq(vdev, queue_idx++, vqi->callback,
> vqi->name, vqi->ctx,
> +=======
> + vqs[i] = vp_setup_vq(vdev, i, callbacks[i], names[i],
> + ctx ? ctx[i] : false,
> +>>>>>>> f814759f80b7... virtio: fix vq # for balloon
This still has merge markers in it.
Thanks,
-- Daniel
