[PATCH 4/8] iommu: Add static iommu_ops->release_domain

Lu Baolu
2024-03-05T12:27:34Z

The current device_release callback for individual iommu drivers does the
following:

1) Silent IOMMU DMA translation: It detaches any existing domain from the
device and puts it into a blocking state (some drivers might use the
identity state).
2) Resource release: It releases resources allocated during the
device_probe callback and restores the device to its pre-probe state.

Step 1 is challenging for individual iommu drivers because each must check
if a domain is already attached to the device. Additionally, if a deferred
attach never occurred, the device_release should avoid modifying hardware
configuration regardless of the reason for its call.

To simplify this process, introduce a static release_domain within the
iommu_ops structure. It can be either a blocking or identity domain
depending on the iommu hardware. The iommu core will decide whether to
attach this domain before the device_release callback, eliminating the
need for repetitive code in various drivers.

Consequently, the device_release callback can focus solely on the opposite
operations of device_probe, including releasing all resources allocated
during that callback.

Co-developed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20240305013305.204605-2-baolu.lu@linux.intel.com
---
include/linux/iommu.h | 1 +
drivers/iommu/iommu.c | 19 +++++++++++++++----
2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index af6c367ed673..2e925b5eba53 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -585,6 +585,7 @@ struct iommu_ops {
struct module *owner;
struct iommu_domain *identity_domain;
struct iommu_domain *blocked_domain;
+ struct iommu_domain *release_domain;
struct iommu_domain *default_domain;
};

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index eb50543bf956..098869007c69 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -462,13 +462,24 @@ static void iommu_deinit_device(struct device *dev)

/*
* release_device() must stop using any attached domain on the device.
- * If there are still other devices in the group they are not effected
+ * If there are still other devices in the group, they are not affected
* by this callback.
*
- * The IOMMU driver must set the device to either an identity or
- * blocking translation and stop using any domain pointer, as it is
- * going to be freed.
+ * If the iommu driver provides release_domain, the core code ensures
+ * that domain is attached prior to calling release_device. Drivers can
+ * use this to enforce a translation on the idle iommu. Typically, the
+ * global static blocked_domain is a good choice.
+ *
+ * Otherwise, the iommu driver must set the device to either an identity
+ * or a blocking translation in release_device() and stop using any
+ * domain pointer, as it is going to be freed.
+ *
+ * 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 (ops->release_device)
ops->release_device(dev);

--
2.34.1