> -----Original Message----- > From: Jan Beulich [mailto:jbeul...@suse.com] > Sent: 27 November 2018 15:50 > To: Paul Durrant <paul.durr...@citrix.com> > Cc: Brian Woods <brian.wo...@amd.com>; Suravee Suthikulpanit > <suravee.suthikulpa...@amd.com>; xen-devel <xen- > de...@lists.xenproject.org> > Subject: RE: [Xen-devel] [PATCH] amd-iommu: remove page merging code > > >>> On 27.11.18 at 15:20, <paul.durr...@citrix.com> wrote: > >> -----Original Message----- > >> From: Jan Beulich [mailto:jbeul...@suse.com] > >> Sent: 27 November 2018 13:07 > >> To: Paul Durrant <paul.durr...@citrix.com> > >> Cc: Brian Woods <brian.wo...@amd.com>; Suravee Suthikulpanit > >> <suravee.suthikulpa...@amd.com>; xen-devel <xen- > >> de...@lists.xenproject.org> > >> Subject: Re: [Xen-devel] [PATCH] amd-iommu: remove page merging code > >> > >> >>> On 26.11.18 at 18:30, <paul.durr...@citrix.com> wrote: > >> > The page merging logic makes use of bits 1-8 and bit 63 of a PTE, > which > >> used > >> > to be specified as ignored. However, bits 5 and 6 are now specified > as > >> > 'accessed' and 'dirty' bits and their use only remains safe as long > as > >> > the DTE 'Host Access Dirty' bits remain clear. > >> > >> Upon second thought - is this actually true with the XSA-275 > >> changes in place? As long as the domain is not running yet, > >> how would A and/or D bits get set? > > > > Ok, I can amend the comment. The risk is, as I say, predicated on the > bits > > in the DTE anyway but the tables are wired into the DTE *before* being > > populated so I don't think there is anything to stop h/w DMAing whilst > they > > are being constructed. > > This way of thinking recurs: When the tables get constructed, the > domain doesn't run yet, or has no device assigned yet. In both > cases I can't see who/what would initiate DMA. >
Ah yes. I was thinking that the page table construction was asynchronous with the assignment for some reason. Paul > Jan > _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
