[PATCH RFC v1 3/5] KVM: guest_memfd: Call arch invalidation hooks when converting to shared

Michael Roth
2025-06-13T00:56:27Z

When guest_memfd is used for both shared/private memory, converting
pages to shared may require kvm_arch_gmem_invalidate() to be issued to
return the pages to an architecturally-defined "shared" state if the
pages were previously allocated and transitioned to a private state via
kvm_arch_gmem_prepare().

Handle this by issuing the appropriate kvm_arch_gmem_invalidate() calls
when converting ranges in the filemap to a shared state.

Signed-off-by: Michael Roth <michael.roth@amd.com>
---
virt/kvm/guest_memfd.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index b77cdccd340e..f27e1f3962bb 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -203,6 +203,28 @@ static int kvm_gmem_shareability_apply(struct inode *inode,
struct maple_tree *mt;

mt = &kvm_gmem_private(inode)->shareability;
+
+ /*
+ * If a folio has been allocated then it was possibly in a private
+ * state prior to conversion. Ensure arch invalidations are issued
+ * to return the folio to a normal/shared state as defined by the
+ * architecture before tracking it as shared in gmem.
+ */
+ if (m == SHAREABILITY_ALL) {
+ pgoff_t idx;
+
+ for (idx = work->start; idx < work->start + work->nr_pages; idx++) {
+ struct folio *folio = filemap_lock_folio(inode->i_mapping, idx);
+
+ if (!IS_ERR(folio)) {
+ kvm_arch_gmem_invalidate(folio_pfn(folio),
+ folio_pfn(folio) + folio_nr_pages(folio));
+ folio_unlock(folio);
+ folio_put(folio);
+ }
+ }
+ }
+
return kvm_gmem_shareability_store(mt, work->start, work->nr_pages, m);
}

--
2.25.1