On 26.07.2019 16:26, Paul Durrant wrote: >> From: Jan Beulich <jbeul...@suse.com> >> Sent: 26 July 2019 15:02 >> >> On 26.07.2019 15:39, Paul Durrant wrote: >>> ? I don't think 'private-pt' or 'separate-pt' really capture the fact that >>> the page tables match the >> P2M. They could just as easily be taken to mean that they are populated >> using some other policy. >> >> But haven't we recently seen that this fully lock-step population >> of page tables isn't always correct (or at least desirable)? I >> vaguely recall other comments to that effect too, from long ago. >> I'd specifically want to avoid encoding into the interface here >> that the two are exact mirrors of one another, now and forever. > > How do you think we should express it. I agree that it's a bit awkward > because of the difference between HVM and PV domains, but all we can do there > really is document it I think, so perhaps the manpage could have something > like:
Sounds reasonable - it at least avoids making the behavior too much spelled out with regard to the similarity of mappings between IOMMU page tables and P2M. There's one issue though: > 'off' > > IOMMU mappings are disabled for the domain and so hardware may not be passed > through. > > 'sync-pt' > > For a PV domain, all writable pages assigned to the domain are identity > mapped by MFN in the IOMMU page tables. Thus a device driver running in the > domain may program passthrough hardware for DMA using MFN values (i.e. > host/machine frame numbers) looked up in its P2M. > For an HVM domain, all non-foreign RAM pages present in the P2M will be > identity mapped by GFN Why "identity mapped" here? It's a GFN -> MFN mappingm, isn't it? Jan > in the IOMMU page tables. Thus a device driver running in the domain may > program passthrough hardware using GFN values (i.e. guest physical frame > numbers) without any further translation. > > 'share-pt' > > This is unavailable for a PV domain. For an HVM domain, this option means > that the IOMMU will be programmed to directly reference the P2M as its page > tables. This availability of this option is hardware specific and thus, if it > is specified for a domain running on hardware that does not allow it, > 'sync-pt' will be used instead. > > ? > > Paul > >> >> Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
