On Wed, Nov 02, 2022 at 05:07:00PM -0500, Michael Roth wrote: > On Thu, Nov 03, 2022 at 12:14:04AM +0300, Kirill A. Shutemov wrote: > > On Mon, Oct 31, 2022 at 12:47:38PM -0500, Michael Roth wrote: > > > > > > In v8 there was some discussion about potentially passing the page/folio > > > and order as part of the invalidation callback, I ended up needing > > > something similar for SEV-SNP, and think it might make sense for other > > > platforms. This main reasoning is: > > > > > > 1) restoring kernel directmap: > > > > > > Currently SNP (and I believe TDX) need to either split or remove kernel > > > direct mappings for restricted PFNs, since there is no guarantee that > > > other PFNs within a 2MB range won't be used for non-restricted > > > (which will cause an RMP #PF in the case of SNP since the 2MB > > > mapping overlaps with guest-owned pages) > > > > That's news to me. Where the restriction for SNP comes from? > > Sorry, missed your first question. > > For SNP at least, the restriction is documented in APM Volume 2, Section > 15.36.10, First row of Table 15-36 (preceeding paragraph has more > context). I forgot to mention this is only pertaining to writes by the > host to 2MB pages that contain guest-owned subpages, for reads it's > not an issue, but I think the implementation requirements end up being > the same either way: > > https://www.amd.com/system/files/TechDocs/24593.pdf Looks like you wanted restricted memfd to be backed by secretmem rather then normal memfd. It would help preserve directmap. -- Kiryl Shutsemau / Kirill A. Shutemov
