On Thu, Sep 24, 2015 at 11:32:29AM -0600, Alex Williamson wrote: > On Thu, 2015-09-24 at 14:33 +1000, David Gibson wrote: > > When we have guest visible IOMMUs, we allow notifiers to be registered > > which will be informed of all changes to IOMMU mappings. This is used by > > vfio to keep the host IOMMU mappings in sync with guest IOMMU mappings. > > > > However, unlike with a memory region listener, an iommu notifier won't be > > told about any mappings which already exist in the (guest) IOMMU at the > > time it is registered. This can cause problems if hotplugging a VFIO > > device onto a guest bus which had existing guest IOMMU mappings, but didn't > > previously have an VFIO devices (and hence no host IOMMU mappings). > > > > This adds a memory_region_register_iommu_notifier_replay() function to > > handle this case. As well as registering the new notifier it replays > > existing mappings. Because the IOMMU memory region doesn't internally > > remember the granularity of the guest IOMMU it has a small hack where the > > caller must specify a granularity at which to replay mappings. > > > > If there are finer mappings in the guest IOMMU these will be reported in > > the iotlb structures passed to the notifier which it must handle (probably > > causing it to flag an error). This isn't new - the VFIO iommu notifier > > must already handle notifications about guest IOMMU mappings too short > > for it to represent in the host IOMMU. > > > > Signed-off-by: David Gibson <da...@gibson.dropbear.id.au>
[snip]
> > +void memory_region_register_iommu_notifier_replay(MemoryRegion *mr,
> > Notifier *n,
> > + hwaddr granularity,
> > + bool is_write)
> > +{
> > + hwaddr addr;
> > + IOMMUTLBEntry iotlb;
> > +
> > + memory_region_register_iommu_notifier(mr, n);
> > +
> > + for (addr = 0; addr < memory_region_size(mr); addr += granularity) {
> > +
> > + iotlb = mr->iommu_ops->translate(mr, addr, is_write);
> > + if (iotlb.perm != IOMMU_NONE) {
> > + n->notify(n, &iotlb);
> > + }
> > + }
> > +}
> > +
>
>
> When memory_listener_register() replays mappings, it does so on an rcu
> copy of the flatview for each AddressSpace. Here we don't seem to have
> anything protecting against concurrency... do we need to worry about
> that?
I was assuming that the IOMMU mappings are protected by the BQL. I
_think_ that's the case (for every IOMMU we have so far), but I'm not
really sure how to be sure.
>
> > void memory_region_unregister_iommu_notifier(Notifier *n)
> > {
> > notifier_remove(n);
>
>
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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