[PATCH] KVM: guest_memfd: Return gmem page as non-refcounted

[Yan Zhao]

Have kvm_gmem_get_pfn() put gmem page refcount before releasing filemap
invalidate lock and return the gmem page as non-refcounted. This avoids
gmem memory attribute conversion failure caused by temporarily holding gmem
page after faulting and before completing mapping.

guest_memfd always holds gmem page in filemap cache. TDX does not increment
gmem page refcount when having gmem pages mapped in S-EPT. Additionally,
as gmem pages are not swappable, setting dirty or accessed bit is not
necessary. Therefore, there's no need to treat gmem pages as refcounted
pages.

Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
---
 virt/kvm/guest_memfd.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 2115e73e455a..e357b4ffa777 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -1332,11 +1332,10 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
 #endif
 
 	folio_unlock(folio);
+	folio_put(folio);
 
 	if (!r)
-		*page = folio_file_page(folio, index);
-	else
-		folio_put(folio);
+		*page = NULL;
 
 out:
 	filemap_invalidate_unlock_shared(file_inode(file)->i_mapping);
-- 
2.43.2