1 files changed, 32 insertions, 13 deletions

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index fbca8c0972da..ffadc5ee8e04 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -623,31 +623,50 @@ err:
 	return r;
 }
 
-void kvm_gmem_unbind(struct kvm_memory_slot *slot)
+static void __kvm_gmem_unbind(struct kvm_memory_slot *slot, struct kvm_gmem *gmem)
 {
 	unsigned long start = slot->gmem.pgoff;
 	unsigned long end = start + slot->npages;
-	struct kvm_gmem *gmem;
+
+	xa_store_range(&gmem->bindings, start, end - 1, NULL, GFP_KERNEL);
+
+	/*
+	 * synchronize_srcu(&kvm->srcu) ensured that kvm_gmem_get_pfn()
+	 * cannot see this memslot.
+	 */
+	WRITE_ONCE(slot->gmem.file, NULL);
+}
+
+void kvm_gmem_unbind(struct kvm_memory_slot *slot)
+{
 	struct file *file;
 
 	/*
-	 * Nothing to do if the underlying file was already closed (or is being
-	 * closed right now), kvm_gmem_release() invalidates all bindings.
+	 * Nothing to do if the underlying file was _already_ closed, as
+	 * kvm_gmem_release() invalidates and nullifies all bindings.
 	 */
-	file = kvm_gmem_get_file(slot);
-	if (!file)
+	if (!slot->gmem.file)
 		return;
 
-	gmem = file->private_data;
-
-	filemap_invalidate_lock(file->f_mapping);
-	xa_store_range(&gmem->bindings, start, end - 1, NULL, GFP_KERNEL);
+	file = kvm_gmem_get_file(slot);
 
 	/*
-	 * synchronize_srcu(&kvm->srcu) ensured that kvm_gmem_get_pfn()
-	 * cannot see this memslot.
+	 * However, if the file is _being_ closed, then the bindings need to be
+	 * removed as kvm_gmem_release() might not run until after the memslot
+	 * is freed.  Note, modifying the bindings is safe even though the file
+	 * is dying as kvm_gmem_release() nullifies slot->gmem.file under
+	 * slots_lock, and only puts its reference to KVM after destroying all
+	 * bindings.  I.e. reaching this point means kvm_gmem_release() hasn't
+	 * yet destroyed the bindings or freed the gmem_file, and can't do so
+	 * until the caller drops slots_lock.
 	 */
-	WRITE_ONCE(slot->gmem.file, NULL);
+	if (!file) {
+		__kvm_gmem_unbind(slot, slot->gmem.file->private_data);
+		return;
+	}
+
+	filemap_invalidate_lock(file->f_mapping);
+	__kvm_gmem_unbind(slot, file->private_data);
 	filemap_invalidate_unlock(file->f_mapping);
 
 	fput(file);