On 26.07.2019 16:54, Paul Durrant wrote: >> -----Original Message----- >> From: Jan Beulich <jbeul...@suse.com> >> Sent: 26 July 2019 15:34 >> To: Paul Durrant <paul.durr...@citrix.com> >> Cc: xen-devel (xen-devel@lists.xenproject.org) >> <xen-devel@lists.xenproject.org> >> Subject: Re: [Xen-devel] per-domain passthrough/iommu options >> >> 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? > > Yes... it's hard to express. What I want to say, of course, is that device > drivers can use GFNs. Can you think of any other form of words that might be > better?
Just omit "identity" in the HVM related sentence? Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
