[PATCH v1 1/6] iommu: Generic support for RMRs during device release

Nicolin Chen
2025-10-12T23:58:02Z

From: Jason Gunthorpe <jgg@nvidia.com>

Generally an IOMMU driver should leave the translation as BLOCKED until the
translation entry is probed onto a struct device. When the struct device is
removed, the translation should be put back to BLOCKED.

Drivers that are able to work like this can set their release_domain to the
blocking domain, and the core code handles this work.

The exception is when the device has an IOMMU_RESV_DIRECT region, in which
case the OS should continuously allow translations for the given range. And
the core code generally prevents using a BLOCKED domain with this device.

Continue this logic for the device release and hoist some open coding from
drivers. If the device has dev->iommu->require_direct and the driver uses a
BLOCKED release_domain, override it to IDENTITY to preserve the semantics.

The only remaining required driver code for IOMMU_RESV_DIRECT should preset
an IDENTITY translation during early IOMMU startup for those devices.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
drivers/iommu/iommu.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 59244c744eabd..adef1a37f9311 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -542,8 +542,20 @@ static void iommu_deinit_device(struct device *dev)
* Regardless, if a delayed attach never occurred, then the release
* should still avoid touching any hardware configuration either.
*/
- if (!dev->iommu->attach_deferred && ops->release_domain)
- ops->release_domain->ops->attach_dev(ops->release_domain, dev);
+ if (!dev->iommu->attach_deferred && ops->release_domain) {
+ struct iommu_domain *release_domain = ops->release_domain;
+
+ /*
+ * If the device requires direct mappings then it should not
+ * be parked on a BLOCKED domain during release as that would
+ * break the direct mappings.
+ */
+ if (dev->iommu->require_direct && ops->identity_domain &&
+ release_domain == ops->blocked_domain)
+ release_domain = ops->identity_domain;
+
+ release_domain->ops->attach_dev(release_domain, dev);
+ }

if (ops->release_device)
ops->release_device(dev);
--
2.43.0