| Message ID | 20240711222755.57476-3-pbonzini@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: guest_memfd: lazy preparation of pages + prefault support for SEV-SNP | expand |
On Thu, Jul 11, 2024 at 06:27:45PM -0400, Paolo Bonzini wrote: > The up-to-date flag as is now is not too useful; it tells guest_memfd not > to overwrite the contents of a folio, but it doesn't say that the page > is ready to be mapped into the guest. For encrypted guests, mapping > a private page requires that the "preparation" phase has succeeded, > and at the same time the same page cannot be prepared twice. > > So, ensure that folio_mark_uptodate() is only called on a prepared page. If > kvm_gmem_prepare_folio() or the post_populate callback fail, the folio > will not be marked up-to-date; it's not a problem to call clear_highpage() > again on such a page prior to the next preparation attempt. > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Michael Roth <michael.roth@amd.com>
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 522e1b28e7ae..1ea632dbae57 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -73,8 +73,6 @@ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index, bool for (i = 0; i < nr_pages; i++) clear_highpage(folio_page(folio, i)); - - folio_mark_uptodate(folio); } if (prepare) { @@ -84,6 +82,8 @@ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index, bool folio_put(folio); return ERR_PTR(r); } + + folio_mark_uptodate(folio); } /* @@ -646,6 +646,8 @@ long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long p = src ? src + i * PAGE_SIZE : NULL; ret = post_populate(kvm, gfn, pfn, p, max_order, opaque); + if (!ret) + folio_mark_uptodate(folio); folio_put(folio); if (ret)
The up-to-date flag as is now is not too useful; it tells guest_memfd not to overwrite the contents of a folio, but it doesn't say that the page is ready to be mapped into the guest. For encrypted guests, mapping a private page requires that the "preparation" phase has succeeded, and at the same time the same page cannot be prepared twice. So, ensure that folio_mark_uptodate() is only called on a prepared page. If kvm_gmem_prepare_folio() or the post_populate callback fail, the folio will not be marked up-to-date; it's not a problem to call clear_highpage() again on such a page prior to the next preparation attempt. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- virt/kvm/guest_memfd.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)