Merge tag 'for-linus-iommufd' of git://git.kernel.org/pub/scm/linux/kernel/git/jgg/iommufd

Pull iommufd updates from Jason Gunthorpe:
 "Just two syzkaller fixes, both for the same basic issue: using the
  area pointer during an access forced unmap while the locks protecting
  it were let go"

* tag 'for-linus-iommufd' of git://git.kernel.org/pub/scm/linux/kernel/git/jgg/iommufd:
  iommufd: Call iopt_area_contig_done() under the lock
  iommufd: Do not access the area pointer after unlocking

Author: torvalds

drivers/iommu/iommufd/device.c

@@ -553,8 +553,8 @@ void iommufd_access_unpin_pages(struct iommufd_access *access,
 			iopt_area_iova_to_index(
 				area,
 				min(last_iova, iopt_area_last_iova(area))));
-	up_read(&iopt->iova_rwsem);
 	WARN_ON(!iopt_area_contig_done(&iter));
+	up_read(&iopt->iova_rwsem);
 }
 EXPORT_SYMBOL_NS_GPL(iommufd_access_unpin_pages, IOMMUFD);
 

drivers/iommu/iommufd/io_pagetable.c

@@ -458,6 +458,7 @@ static int iopt_unmap_iova_range(struct io_pagetable *iopt, unsigned long start,
 {
 	struct iopt_area *area;
 	unsigned long unmapped_bytes = 0;
+	unsigned int tries = 0;
 	int rc = -ENOENT;
 
 	/*
@@ -484,19 +485,26 @@ static int iopt_unmap_iova_range(struct io_pagetable *iopt, unsigned long start,
 			goto out_unlock_iova;
 		}
 
+		if (area_first != start)
+			tries = 0;
+
 		/*
 		 * num_accesses writers must hold the iova_rwsem too, so we can
 		 * safely read it under the write side of the iovam_rwsem
 		 * without the pages->mutex.
 		 */
 		if (area->num_accesses) {
+			size_t length = iopt_area_length(area);
+
 			start = area_first;
 			area->prevent_access = true;
 			up_write(&iopt->iova_rwsem);
 			up_read(&iopt->domains_rwsem);
-			iommufd_access_notify_unmap(iopt, area_first,
-						    iopt_area_length(area));
-			if (WARN_ON(READ_ONCE(area->num_accesses)))
+
+			iommufd_access_notify_unmap(iopt, area_first, length);
+			/* Something is not responding to unmap requests. */
+			tries++;
+			if (WARN_ON(tries > 100))
 				return -EDEADLOCK;
 			goto again;
 		}