Virtualization - Dec 2020 - [RFC v2 09/13] vduse: Add support for processing vhost iotlb message

----- Original Message -----
> On Mon, Dec 28, 2020 at 4:43 PM Jason Wang <jasowang at redhat.com>
wrote:
> >
> >
> > On 2020/12/28 ??4:14, Yongji Xie wrote:
> > >> 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.
Just to make sure I understand your point.

Do you mean you plan to notify the unmap of 1) streaming DMA or 2)
coherent DMA?

For 1) you probably need a workqueue to do that since dma unmap can
be done in irq or bh context. And if usrspace does't do the unmap, it
can still access the bounce buffer (if you don't zap pte)?

Thanks

> 
> Thanks,
> Yongji
> 
>