Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier

[Jason Wang]

On 2020/7/3 下午9:03, Peter Xu wrote:
> On Fri, Jul 03, 2020 at 03:24:19PM +0800, Jason Wang wrote:
> > On 2020/7/2 下午11:45, Peter Xu wrote:
> > > On Thu, Jul 02, 2020 at 11:01:54AM +0800, Jason Wang wrote:
> > > > So I think we agree that a new notifier is needed?
> > > Good to me, or a new flag should be easier (IOMMU_NOTIFIER_DEV_IOTLB)?
> >
> > That should work but I wonder something as following is better.
> >
> > Instead of introducing new flags, how about carry the type of event in the
> > notifier then the device (vhost) can choose the message it want to process
> > like:
> >
> > static vhost_iommu_event(IOMMUNotifier *n, IOMMUTLBEvent *event)
> >
> > {
> >
> > switch (event->type) {
> >
> > case IOMMU_MAP:
> > case IOMMU_UNMAP:
> > case IOMMU_DEV_IOTLB_UNMAP:
> > ...
> >
> > }
> Looks ok to me, though imo we should still keep the registration information,
> so VT-d knows which notifiers is interested in which events.  E.g., we can
> still do something like vtd_as_has_map_notifier().


Is this for a better performance?

I wonder whether it's worth since we can't not have both vhost and vtd 
to be registered into the same as.

So it should be functional equivalent to vtd_as_has_notifier().

Thanks


> So these are probably two different things: the new IOMMU_NOTIFIER_DEV_IOTLB
> flag is one as discussed; the other one is whether we would like to introduce
> IOMMUTLBEvent to include the type, so that we can avoid introduce two notifiers
> for one device majorly to identify dev-iotlb from unmaps.
>
> Thanks,