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SubjectRe: [PATCH] mic: vop: Fix broken virtqueues
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On Tue, 2019-01-29 at 11:22 +0100, Vincent Whitchurch wrote:
> VOP is broken in mainline since commit 1ce9e6055fa0a9043 ("virtio_ring:
> introduce packed ring support"); attempting to use the virtqueues leads
> to various kernel crashes. I'm testing it with my not-yet-merged
> loopback patches, but even the in-tree MIC hardware cannot work.
>
> The problem is not in the referenced commit per se, but is due to the
> following hack in vop_find_vq() which depends on the layout of private
> structures in other source files, which that commit happened to change:
>
> /*
> * To reassign the used ring here we are directly accessing
> * struct vring_virtqueue which is a private data structure
> * in virtio_ring.c. At the minimum, a BUILD_BUG_ON() in
> * vring_new_virtqueue() would ensure that
> * (&vq->vring == (struct vring *) (&vq->vq + 1));
> */
> vr = (struct vring *)(vq + 1);
> vr->used = used;
>
> Fix vop by using __vring_new_virtqueue() to create the needed vring
> layout from the start, instead of attempting to patch in the used ring
> later. __vring_new_virtqueue() was added way back in commit
> 2a2d1382fe9dcc ("virtio: Add improved queue allocation API") in order to
> address mic's usecase, according to the commit message.
>

Thank you for fixing this up Vincent.

Reviewed-by: Sudeep Dutt <sudeep.dutt@intel.com>

> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
> ---
> drivers/misc/mic/vop/vop_main.c | 60 +++++++++++++++++++--------------
> 1 file changed, 34 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/misc/mic/vop/vop_main.c b/drivers/misc/mic/vop/vop_main.c
> index d2b9782eee87..fef45bf6d519 100644
> --- a/drivers/misc/mic/vop/vop_main.c
> +++ b/drivers/misc/mic/vop/vop_main.c
> @@ -284,6 +284,26 @@ static void vop_del_vqs(struct virtio_device *dev)
> vop_del_vq(vq, idx++);
> }
>
> +static struct virtqueue *vop_new_virtqueue(unsigned int index,
> + unsigned int num,
> + struct virtio_device *vdev,
> + bool context,
> + void *pages,
> + bool (*notify)(struct virtqueue *vq),
> + void (*callback)(struct virtqueue *vq),
> + const char *name,
> + void *used)
> +{
> + bool weak_barriers = false;
> + struct vring vring;
> +
> + vring_init(&vring, num, pages, MIC_VIRTIO_RING_ALIGN);
> + vring.used = used;
> +
> + return __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
> + notify, callback, name);
> +}
> +
> /*
> * This routine will assign vring's allocated in host/io memory. Code in
> * virtio_ring.c however continues to access this io memory as if it were local
> @@ -303,7 +323,6 @@ static struct virtqueue *vop_find_vq(struct virtio_device *dev,
> struct _mic_vring_info __iomem *info;
> void *used;
> int vr_size, _vr_size, err, magic;
> - struct vring *vr;
> u8 type = ioread8(&vdev->desc->type);
>
> if (index >= ioread8(&vdev->desc->num_vq))
> @@ -322,17 +341,7 @@ static struct virtqueue *vop_find_vq(struct virtio_device *dev,
> return ERR_PTR(-ENOMEM);
> vdev->vr[index] = va;
> memset_io(va, 0x0, _vr_size);
> - vq = vring_new_virtqueue(
> - index,
> - le16_to_cpu(config.num), MIC_VIRTIO_RING_ALIGN,
> - dev,
> - false,
> - ctx,
> - (void __force *)va, vop_notify, callback, name);
> - if (!vq) {
> - err = -ENOMEM;
> - goto unmap;
> - }
> +
> info = va + _vr_size;
> magic = ioread32(&info->magic);
>
> @@ -341,7 +350,6 @@ static struct virtqueue *vop_find_vq(struct virtio_device *dev,
> goto unmap;
> }
>
> - /* Allocate and reassign used ring now */
> vdev->used_size[index] = PAGE_ALIGN(sizeof(__u16) * 3 +
> sizeof(struct vring_used_elem) *
> le16_to_cpu(config.num));
> @@ -351,8 +359,17 @@ static struct virtqueue *vop_find_vq(struct virtio_device *dev,
> err = -ENOMEM;
> dev_err(_vop_dev(vdev), "%s %d err %d\n",
> __func__, __LINE__, err);
> - goto del_vq;
> + goto unmap;
> + }
> +
> + vq = vop_new_virtqueue(index, le16_to_cpu(config.num), dev, ctx,
> + (void __force *)va, vop_notify, callback,
> + name, used);
> + if (!vq) {
> + err = -ENOMEM;
> + goto free_used;
> }
> +
> vdev->used[index] = dma_map_single(&vpdev->dev, used,
> vdev->used_size[index],
> DMA_BIDIRECTIONAL);
> @@ -360,26 +377,17 @@ static struct virtqueue *vop_find_vq(struct virtio_device *dev,
> err = -ENOMEM;
> dev_err(_vop_dev(vdev), "%s %d err %d\n",
> __func__, __LINE__, err);
> - goto free_used;
> + goto del_vq;
> }
> writeq(vdev->used[index], &vqconfig->used_address);
> - /*
> - * To reassign the used ring here we are directly accessing
> - * struct vring_virtqueue which is a private data structure
> - * in virtio_ring.c. At the minimum, a BUILD_BUG_ON() in
> - * vring_new_virtqueue() would ensure that
> - * (&vq->vring == (struct vring *) (&vq->vq + 1));
> - */
> - vr = (struct vring *)(vq + 1);
> - vr->used = used;
>
> vq->priv = vdev;
> return vq;
> +del_vq:
> + vring_del_virtqueue(vq);
> free_used:
> free_pages((unsigned long)used,
> get_order(vdev->used_size[index]));
> -del_vq:
> - vring_del_virtqueue(vq);
> unmap:
> vpdev->hw_ops->unmap(vpdev, vdev->vr[index]);
> return ERR_PTR(err);


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