[PATCH 2/5] iommu: Add domain_alloc_identity()

Jason Gunthorpe
2025-02-07T14:46:14Z

virtio-iommu has a mode where the IDENTITY domain is actually a paging
domain with an identity mapping covering some of the system address
space manually created.

To support this add a new domain_alloc_identity() op that accepts
the struct device so that virtio can allocate and fully finalize a
paging domain to return.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
drivers/iommu/iommu.c | 20 ++++++++++++--------
include/linux/iommu.h | 4 ++++
2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 870c3cdbd0f622..ee33d26dfcd40d 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1595,15 +1595,19 @@ static struct iommu_domain *__iommu_alloc_identity_domain(struct device *dev)
if (ops->identity_domain)
return ops->identity_domain;

- /* Older drivers create the identity domain via ops->domain_alloc() */
- if (!ops->domain_alloc)
+ if (ops->domain_alloc_identity) {
+ domain = ops->domain_alloc_identity(dev);
+ if (IS_ERR(domain))
+ return domain;
+ } else if (ops->domain_alloc) {
+ domain = ops->domain_alloc(IOMMU_DOMAIN_IDENTITY);
+ if (!domain)
+ return ERR_PTR(-ENOMEM);
+ if (IS_ERR(domain))
+ return domain;
+ } else {
return ERR_PTR(-EOPNOTSUPP);
-
- domain = ops->domain_alloc(IOMMU_DOMAIN_IDENTITY);
- if (IS_ERR(domain))
- return domain;
- if (!domain)
- return ERR_PTR(-ENOMEM);
+ }

iommu_domain_init(domain, IOMMU_DOMAIN_IDENTITY, ops);
return domain;
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 38c65e92ecd091..6389d59178ba3f 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -557,6 +557,9 @@ iommu_copy_struct_from_full_user_array(void *kdst, size_t kdst_entry_size,
* @domain_alloc: allocate and return an iommu domain if success. Otherwise
* NULL is returned. The domain is not fully initialized until
* the caller iommu_domain_alloc() returns.
+ * @domain_alloc_identity: allocate an IDENTITY domain. Drivers should prefer to
+ * use identity_domain instead. This should only be used
+ * if dynamic logic is necessary.
* @domain_alloc_paging_flags: Allocate an iommu domain corresponding to the
* input parameters as defined in
* include/uapi/linux/iommufd.h. The @user_data can be
@@ -615,6 +618,7 @@ struct iommu_ops {

/* Domain allocation and freeing by the iommu driver */
struct iommu_domain *(*domain_alloc)(unsigned iommu_domain_type);
+ struct iommu_domain *(*domain_alloc_identity)(struct device *dev);
struct iommu_domain *(*domain_alloc_paging_flags)(
struct device *dev, u32 flags,
const struct iommu_user_data *user_data);
--
2.43.0