[PATCH v7 10/28] iommufd/access: Bypass access->ops->unmap for internal use

Nicolin Chen
2025-06-26T19:56:24Z

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. Instead, it would not implement an unmap handler. Thus, bypass any
access->ops->unmap call when the access is marked as internal. Also error
out the internal case in iommufd_access_notify_unmap() to reject an unmap
operation and propagatethe errno upwards.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Pranjal Shrivastava <praan@google.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
drivers/iommu/iommufd/iommufd_private.h | 4 ++--
drivers/iommu/iommufd/device.c | 21 +++++++++++++++++----
drivers/iommu/iommufd/io_pagetable.c | 10 +++++++++-
3 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index 9d1f55deb9ca..b849099e804b 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 07a4ff753c12..8f078fda795a 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 (!iommufd_access_is_internal(access) && access->ops->unmap) {
mutex_unlock(&access->ioas_lock);
access->ops->unmap(access->data, 0, ULONG_MAX);
mutex_lock(&access->ioas_lock);
@@ -1245,15 +1245,24 @@ 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);
+ /* Bypass any unmap if there is an internal access */
+ xa_for_each(&ioas->iopt.access_list, index, access) {
+ if (iommufd_access_is_internal(access)) {
+ ret = -EBUSY;
+ goto unlock;
+ }
+ }
+
xa_for_each(&ioas->iopt.access_list, index, access) {
if (!iommufd_lock_obj(&access->obj))
continue;
@@ -1264,7 +1273,9 @@ 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;
}

/**
@@ -1362,7 +1373,9 @@ 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 ||
+ (!iommufd_access_is_internal(access) &&
+ !access->ops->unmap)))
return -EINVAL;

if (!length)
diff --git a/drivers/iommu/iommufd/io_pagetable.c b/drivers/iommu/iommufd/io_pagetable.c
index 22fc3a12109f..6b8477b1f94b 100644
--- a/drivers/iommu/iommufd/io_pagetable.c
+++ b/drivers/iommu/iommufd/io_pagetable.c
@@ -740,7 +740,15 @@ 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)) {
--
2.43.0