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

[Nicolin Chen <nicolinc@nvidia.com>]

The access object has been used externally by VFIO mdev devices, allowing
them to pin/unpin physical pages (via needs_pin_pages). Meanwhile, a racy
unmap can occur in this case, so these devices usually implement an unmap
handler, invoked by iommufd_access_notify_unmap().

The new HW queue object will need the same pin/unpin feature, although it
(unlike the mdev case) wants to reject any unmap attempt, during its life
cycle.

To reuse the access object for the new HW queue, allow its access->ops to
be NULL. Error out a NULL access->ops in iommufd_access_notify_unmap() to
reject an unmap operation and propagatethe errno upwards.

Then, update iommufd_access_change_ioas() and iommufd_access_pin_pages(),
to allow this new use case.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
 drivers/iommu/iommufd/iommufd_private.h |  4 ++--
 drivers/iommu/iommufd/device.c          | 15 +++++++++++----
 drivers/iommu/iommufd/io_pagetable.c    | 17 ++++++++++++++---
 3 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index 4f5e8cd99c96..4a375a8c9216 100644
--- a/drivers/iommu/iommufd/iommufd_private.h
+++ b/drivers/iommu/iommufd/iommufd_private.h
@@ -111,8 +111,8 @@ int iopt_read_and_clear_dirty_data(struct io_pagetable *iopt,
 int iopt_set_dirty_tracking(struct io_pagetable *iopt,
 			    struct iommu_domain *domain, bool enable);
 
-void iommufd_access_notify_unmap(struct io_pagetable *iopt, unsigned long iova,
-				 unsigned long length);
+int iommufd_access_notify_unmap(struct io_pagetable *iopt, unsigned long iova,
+				unsigned long length);
 int iopt_table_add_domain(struct io_pagetable *iopt,
 			  struct iommu_domain *domain);
 void iopt_table_remove_domain(struct io_pagetable *iopt,
diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
index e9b6ca47095c..9293722b9cff 100644
--- a/drivers/iommu/iommufd/device.c
+++ b/drivers/iommu/iommufd/device.c
@@ -1048,7 +1048,7 @@ static int iommufd_access_change_ioas(struct iommufd_access *access,
 	}
 
 	if (cur_ioas) {
-		if (access->ops->unmap) {
+		if (access->ops && access->ops->unmap) {
 			mutex_unlock(&access->ioas_lock);
 			access->ops->unmap(access->data, 0, ULONG_MAX);
 			mutex_lock(&access->ioas_lock);
@@ -1204,16 +1204,21 @@ EXPORT_SYMBOL_NS_GPL(iommufd_access_replace, "IOMMUFD");
  * run in the future. Due to this a driver must not create locking that prevents
  * unmap to complete while iommufd_access_destroy() is running.
  */
-void iommufd_access_notify_unmap(struct io_pagetable *iopt, unsigned long iova,
-				 unsigned long length)
+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;
+		}
 		if (!iommufd_lock_obj(&access->obj))
 			continue;
 		xa_unlock(&ioas->iopt.access_list);
@@ -1223,7 +1228,9 @@ void iommufd_access_notify_unmap(struct io_pagetable *iopt, unsigned long iova,
 		iommufd_put_object(access->ictx, &access->obj);
 		xa_lock(&ioas->iopt.access_list);
 	}
+unlock:
 	xa_unlock(&ioas->iopt.access_list);
+	return ret;
 }
 
 /**
@@ -1321,7 +1328,7 @@ int iommufd_access_pin_pages(struct iommufd_access *access, unsigned long iova,
 
 	/* Driver's ops don't support pin_pages */
 	if (IS_ENABLED(CONFIG_IOMMUFD_TEST) &&
-	    WARN_ON(access->iova_alignment != PAGE_SIZE || !access->ops->unmap))
+	    WARN_ON(access->iova_alignment != PAGE_SIZE))
 		return -EINVAL;
 
 	if (!length)
diff --git a/drivers/iommu/iommufd/io_pagetable.c b/drivers/iommu/iommufd/io_pagetable.c
index 13d010f19ed1..6b8477b1f94b 100644
--- a/drivers/iommu/iommufd/io_pagetable.c
+++ b/drivers/iommu/iommufd/io_pagetable.c
@@ -740,11 +740,21 @@ static int iopt_unmap_iova_range(struct io_pagetable *iopt, unsigned long start,
 			up_write(&iopt->iova_rwsem);
 			up_read(&iopt->domains_rwsem);
 
-			iommufd_access_notify_unmap(iopt, area_first, length);
+			rc = iommufd_access_notify_unmap(iopt, area_first,
+							 length);
+			if (rc) {
+				down_read(&iopt->domains_rwsem);
+				down_write(&iopt->iova_rwsem);
+				area->prevent_access = false;
+				goto out_unlock_iova;
+			}
+
 			/* 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;
+			}
 			goto again;
 		}
 
@@ -766,6 +776,7 @@ static int iopt_unmap_iova_range(struct io_pagetable *iopt, unsigned long start,
 out_unlock_iova:
 	up_write(&iopt->iova_rwsem);
 	up_read(&iopt->domains_rwsem);
+out_unmapped:
 	if (unmapped)
 		*unmapped = unmapped_bytes;
 	return rc;
-- 
2.43.0