linux-kernel - [PATCH v1 05/12] iommu: Introduce get_viommu_size and viommu

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Message-ID: <bc2c57254c40028e4dc74f32ac350826a26b3d8c.1749488870.git.nicolinc@nvidia.com>
Date: Mon, 9 Jun 2025 10:13:28 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: <jgg@...dia.com>, <kevin.tian@...el.com>
CC: <will@...nel.org>, <robin.murphy@....com>, <joro@...tes.org>,
	<ddutile@...hat.com>, <yi.l.liu@...el.com>, <peterz@...radead.org>,
	<jsnitsel@...hat.com>, <praan@...gle.com>,
	<linux-arm-kernel@...ts.infradead.org>, <iommu@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, <patches@...ts.linux.dev>,
	<baolu.lu@...ux.intel.com>
Subject: [PATCH v1 05/12] iommu: Introduce get_viommu_size and viommu_init ops

So far, a vIOMMU object has been allocated by IOMMU driver and initialized
with the driver-level structure, before it returns to the iommufd core for
core-level structure initialization. It has been requiring iommufd core to
expose some core structure/helpers in its driver.c file, which result in a
size increase of this driver module.

Meanwhile, IOMMU drivers are now requiring more vIOMMU-base structures for
some advanced feature, such as the existing vDEVICE and a future HW_QUEUE.
Initializing a core-structure later than driver-structure gives for-driver
helpers some trouble, when they are used by IOMMU driver assuming that the
new structure (including core) are fully initialized, for example:
    // my_viommu is successfully allocated
    my_viommu = iommufd_viommu_alloc(...);
    // This may crash if it reads viommu->ictx
    new = iommufd_new_viommu_helper(my_viommu->core ...);

To ease such a condition, allow the IOMMU driver to report the size of its
vIOMMU structure, let the core allocate a vIOMMU object and initialize the
core-level structure first, and then hand it over the driver to initialize
its driver-level structure.

Thus, this requires two new iommu ops, get_viommu_size and viommu_init, so
iommufd core can communicate with drivers to replace the viommu_alloc op.

This also adds a VIOMMU_STRUCT_SIZE macro, for drivers to use, which would
statically sanitize the driver structure.

Suggested-by: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
---
 include/linux/iommu.h   | 15 +++++++++++++++
 include/linux/iommufd.h |  6 ++++++
 2 files changed, 21 insertions(+)

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 156732807994..e42a28971182 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -14,6 +14,7 @@
 #include <linux/err.h>
 #include <linux/of.h>
 #include <linux/iova_bitmap.h>
+#include <uapi/linux/iommufd.h>
 
 #define IOMMU_READ	(1 << 0)
 #define IOMMU_WRITE	(1 << 1)
@@ -596,6 +597,16 @@ iommu_copy_struct_from_full_user_array(void *kdst, size_t kdst_entry_size,
  *		- IOMMU_DOMAIN_DMA: must use a dma domain
  *		- 0: use the default setting
  * @default_domain_ops: the default ops for domains
+ * @get_viommu_size: Get the size of a driver-level vIOMMU structure for a given
+ *                   @dev corresponding to @viommu_type. Driver should return an
+ *                   errno if vIOMMU isn't supported accordingly. It is required
+ *                   for driver to use the VIOMMU_STRUCT_SIZE macro to sanitize
+ *                   a driver-level vIOMMU structure related to the core one
+ * @viommu_init: Init the driver-level struct of an iommufd_viommu on a physical
+ *               IOMMU instance @viommu->iommu_dev, as the set of virtualization
+ *               resources shared/passed to user space IOMMU instance. Associate
+ *               it with a nesting @parent_domain. It is required for driver to
+ *               set @viommu->ops pointing to its own viommu_ops
  * @viommu_alloc: Allocate an iommufd_viommu on a physical IOMMU instance behind
  *                the @dev, as the set of virtualization resources shared/passed
  *                to user space IOMMU instance. And associate it with a nesting
@@ -654,6 +665,10 @@ struct iommu_ops {
 
 	int (*def_domain_type)(struct device *dev);
 
+	int (*get_viommu_size)(enum iommu_viommu_type viommu_type,
+			       struct device *dev, size_t *viommu_size);
+	int (*viommu_init)(struct iommufd_viommu *viommu,
+			   struct iommu_domain *parent_domain);
 	struct iommufd_viommu *(*viommu_alloc)(
 		struct device *dev, struct iommu_domain *parent_domain,
 		struct iommufd_ctx *ictx, unsigned int viommu_type);
diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
index ac98e49e44fe..423e08963d90 100644
--- a/include/linux/iommufd.h
+++ b/include/linux/iommufd.h
@@ -229,6 +229,12 @@ static inline int iommufd_viommu_report_event(struct iommufd_viommu *viommu,
 }
 #endif /* CONFIG_IOMMUFD_DRIVER_CORE */
 
+#define VIOMMU_STRUCT_SIZE(drv_struct, member)                                 \
+	(sizeof(drv_struct) +                                                  \
+	 BUILD_BUG_ON_ZERO(offsetof(drv_struct, member)) +                     \
+	 BUILD_BUG_ON_ZERO(!__same_type(struct iommufd_viommu,                 \
+					((drv_struct *)NULL)->member)))
+
 /*
  * Helpers for IOMMU driver to allocate driver structures that will be freed by
  * the iommufd core. The free op will be called prior to freeing the memory.
-- 
2.43.0