Re: [PATCH v6 06/25] iommufd/access: Allow access->ops to be NULL for internal use

On Wed, Jun 25, 2025 at 03:38:19AM +0000, Tian, Kevin wrote:

quoted

From: Nicolin Chen <redacted>
Sent: Saturday, June 14, 2025 3:15 PM

+int iommufd_access_notify_unmap(struct io_pagetable *iopt, unsigned long
iova,
+				unsigned long length)
 {
 	struct iommufd_ioas *ioas =
 		container_of(iopt, struct iommufd_ioas, iopt);
 	struct iommufd_access *access;
 	unsigned long index;
+	int ret = 0;

 	xa_lock(&ioas->iopt.access_list);
 	xa_for_each(&ioas->iopt.access_list, index, access) {
+		if (!access->ops || !access->ops->unmap) {
+			ret = -EBUSY;
+			goto unlock;
+		}

then accesses before this one have been notified to unpin the area
while accesses afterwards are left unnotified.

in the end the unmap fails but with some side-effect incurred.

I'm not sure whether this intermediate state may lead to any undesired
effect later. Just raise it in case you or Jason already thought about it.

That's a good point. When an access blocks the unmap, there is no
unmap happening so no point in notifying devices for ops->unmap.

And, when the function is re-entered, there could be a duplicated
ops->unmap call for those devices that are already notified once?

So, if we play safe, there can be a standalone xa_for_each to dig
for !access->ops->unmap. And it could be a bit cleaner to add an
iommufd_access_has_internal_use() to be called under those rwsems.

quoted

 			/* Something is not responding to unmap requests.
*/
 			tries++;
-			if (WARN_ON(tries > 100))
-				return -EDEADLOCK;
+			if (WARN_ON(tries > 100)) {
+				rc = -EDEADLOCK;
+				goto out_unmapped;
+			}

this looks an unrelated fix?

Yea.. let me separate it out.

Thanks
Nicolin