On Fri, Jul 26, 2024 at 02:51:57PM -0400, Paolo Bonzini wrote: > Right now, large folios are not supported in guest_memfd, and therefore the order > used by kvm_gmem_populate() is always 0. In this scenario, using the up-to-date > bit to track prepared-ness is nice and easy because we have one bit available > per page. > > In the future, however, we might have large pages that are partially populated; > for example, in the case of SEV-SNP, if a large page has both shared and private > areas inside, it is necessary to populate it at a granularity that is smaller > than that of the guest_memfd's backing store. In that case we will have > to track preparedness at a 4K level, probably as a bitmap. > > In preparation for that, do not use explicitly folio_test_uptodate() and > folio_mark_uptodate(). Return the state of the page directly from > __kvm_gmem_get_pfn(), so that it is expected to apply to 2^N pages > with N=*max_order. The function to mark a range as prepared for now > takes just a folio, but is expected to take also an index and order > (or something like that) when large pages are introduced. > > Thanks to Michael Roth for pointing out the issue with large pages. > > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Reviewed-by: Michael Roth <michael.roth@xxxxxxx>
