Re: [virtio-dev] Re: [PATCH V2 2/2] virtio-pci: add PASID configuration extended capability

[Jason Wang <jasowang@redhat.com>]

å 2022/1/13 äå11:17, Michael S. Tsirkin åé:
> On Thu, Jan 13, 2022 at 02:53:36PM +0000, Stefan Hajnoczi wrote:
> > On Thu, Jan 13, 2022 at 05:45:11AM -0500, Michael S. Tsirkin wrote:
> > > On Thu, Jan 13, 2022 at 10:32:11AM +0000, Stefan Hajnoczi wrote:
> > > > > So my understanding is that instead of delaying the response to read
> > > > > it's better to simply present the previous PASID value if there're any
> > > > > pending transactions of previous PASID value. The driver can then
> > > > > choose to poll or using timers etc.
> > > Don't we limit these changes to before DRIVER_OK?
> > > If we do then no previous transactions can exist.
> > Not sure if that's possible for the vDPA virtqueue assignment use case
> > where one large VIRTIO device provides virtqueues for many smaller vDPA
> > devices?


That could be the case but usually a smaller vDPA device requires a 
bunch of hardware resources more than just virtqueues.

Another example is assign a queue directly to userspace with PASID for SVA.


> > Stefan
> Then I guess queue must be stopped?


Yes, since we have virtqueue reset, I can limit the assigning before 
DRIVER_OK or queue(s) are reset. Does this work?

Thanks


>