On Mon, Dec 28, 2020 at 4:43 PM Jason Wang [off-list ref] wrote:

On 2020/12/28 下午4:14, Yongji Xie wrote:

quoted

quoted

I see. So all the above two questions are because VHOST_IOTLB_INVALIDATE
is expected to be synchronous. This need to be solved by tweaking the
current VDUSE API or we can re-visit to go with descriptors relaying first.

Actually all vdpa related operations are synchronous in current
implementation. The ops.set_map/dma_map/dma_unmap should not return
until the VDUSE_UPDATE_IOTLB/VDUSE_INVALIDATE_IOTLB message is replied
by userspace. Could it solve this problem?

  I was thinking whether or not we need to generate IOTLB_INVALIDATE
message to VDUSE during dma_unmap (vduse_dev_unmap_page).

If we don't, we're probably fine.

It seems not feasible. This message will be also used in the
virtio-vdpa case to notify userspace to unmap some pages during
consistent dma unmapping. Maybe we can document it to make sure the
users can handle the message correctly.

Thanks,
Yongji