On Fri, Sep 25, 2015 at 01:20:12PM +0200, Paolo Bonzini wrote: > > > On 24/09/2015 06:33, 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> > > The patch is okay, just two questions: > > 1) Is there a case where using the no-replay functions makes sense?
I'm not sure. I think vfio is the only user so far, so I guess that's
technically a no. I was reluctant to change the interface and
semantics just off the bat, though.
> 2) You could add a ->replay function to the iommu_ops to optimize it, if
> you want.
Yes. Originally I was going to implement with a ->replay function,
before I realised I didn't actually need it. I figure we can optimize
when and if it proves necessary.
--
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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