linux.git/drivers/virtio/virtio_ring.c, branch v6.6

virtio_ring: fix avail_wrap_counter in virtqueue_add_packed

2023-09-03T22:10:24+00:00

In current packed virtqueue implementation, the avail_wrap_counter won't
flip, in the case when the driver supplies a descriptor chain with a
length equals to the queue size; total_sg == vq->packed.vring.num.

Let’s assume the following situation:
vq->packed.vring.num=4
vq->packed.next_avail_idx: 1
vq->packed.avail_wrap_counter: 0

Then the driver adds a descriptor chain containing 4 descriptors.

We expect the following result with avail_wrap_counter flipped:
vq->packed.next_avail_idx: 1
vq->packed.avail_wrap_counter: 1

But, the current implementation gives the following result:
vq->packed.next_avail_idx: 1
vq->packed.avail_wrap_counter: 0

To reproduce the bug, you can set a packed queue size as small as
possible, so that the driver is more likely to provide a descriptor
chain with a length equal to the packed queue size. For example, in
qemu run following commands:
sudo qemu-system-x86_64 \
-enable-kvm \
-nographic \
-kernel "path/to/kernel_image" \
-m 1G \
-drive file="path/to/rootfs",if=none,id=disk \
-device virtio-blk,drive=disk \
-drive file="path/to/disk_image",if=none,id=rwdisk \
-device virtio-blk,drive=rwdisk,packed=on,queue-size=4,\
indirect_desc=off \
-append "console=ttyS0 root=/dev/vda rw init=/bin/bash"

Inside the VM, create a directory and mount the rwdisk device on it. The
rwdisk will hang and mount operation will not complete.

This commit fixes the wrap counter error by flipping the
packed.avail_wrap_counter, when start of descriptor chain equals to the
end of descriptor chain (head == i).

Fixes: 1ce9e6055fa0 ("virtio_ring: introduce packed ring support")
Signed-off-by: Yuan Yao 
Message-Id: <20230808051110.3492693-1-yuanyaogoog@chromium.org>
Acked-by: Jason Wang 
Signed-off-by: Michael S. Tsirkin

virtio_ring: introduce dma sync api for virtqueue

2023-09-03T22:10:23+00:00

These API has been introduced:

* virtqueue_dma_need_sync
* virtqueue_dma_sync_single_range_for_cpu
* virtqueue_dma_sync_single_range_for_device

These APIs can be used together with the premapped mechanism to sync the
DMA address.

Signed-off-by: Xuan Zhuo 
Message-Id: <20230810123057.43407-12-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin

virtio_ring: introduce dma map api for virtqueue

2023-09-03T22:10:23+00:00

Added virtqueue_dma_map_api* to map DMA addresses for virtual memory in
advance. The purpose is to keep memory mapped across multiple add/get
buf operations.

Signed-off-by: Xuan Zhuo 
Message-Id: <20230810123057.43407-11-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin

virtio_ring: introduce virtqueue_reset()

2023-09-03T22:10:23+00:00

Introduce virtqueue_reset() to release all buffer inside vq.

Signed-off-by: Xuan Zhuo 
Acked-by: Jason Wang 
Message-Id: <20230810123057.43407-10-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin

virtio_ring: separate the logic of reset/enable from virtqueue_resize

2023-09-03T22:10:23+00:00

The subsequent reset function will reuse these logic.

Signed-off-by: Xuan Zhuo 
Acked-by: Jason Wang 
Message-Id: <20230810123057.43407-9-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin

virtio_ring: correct the expression of the description of virtqueue_resize()

2023-09-03T22:10:23+00:00

Modify the "useless" to a more accurate "unused".

Signed-off-by: Xuan Zhuo 
Acked-by: Jason Wang 
Message-Id: <20230810123057.43407-8-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin

virtio_ring: skip unmap for premapped

2023-09-03T22:10:23+00:00

Now we add a case where we skip dma unmap, the vq->premapped is true.

We can't just rely on use_dma_api to determine whether to skip the dma
operation. For convenience, I introduced the "do_unmap". By default, it
is the same as use_dma_api. If the driver is configured with premapped,
then do_unmap is false.

So as long as do_unmap is false, for addr of desc, we should skip dma
unmap operation.

Signed-off-by: Xuan Zhuo 
Message-Id: <20230810123057.43407-7-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin

virtio_ring: introduce virtqueue_dma_dev()

2023-09-03T22:10:23+00:00

Added virtqueue_dma_dev() to get DMA device for virtio. Then the
caller can do dma operation in advance. The purpose is to keep memory
mapped across multiple add/get buf operations.

Signed-off-by: Xuan Zhuo 
Acked-by: Jason Wang 
Message-Id: <20230810123057.43407-6-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin

virtio_ring: support add premapped buf

2023-09-03T22:10:23+00:00

If the vq is the premapped mode, use the sg_dma_address() directly.

Signed-off-by: Xuan Zhuo 
Message-Id: <20230810123057.43407-5-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin

virtio_ring: introduce virtqueue_set_dma_premapped()

2023-09-03T22:10:22+00:00

This helper allows the driver change the dma mode to premapped mode.
Under the premapped mode, the virtio core do not do dma mapping
internally.

This just work when the use_dma_api is true. If the use_dma_api is false,
the dma options is not through the DMA APIs, that is not the standard
way of the linux kernel.

Signed-off-by: Xuan Zhuo 
Message-Id: <20230810123057.43407-4-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin