iommufd: Disallow allocating nested parent domain with fault ID

Allocating a domain with a fault ID indicates that the domain is faultable.
However, there is a gap for the nested parent domain to support PRI. Some
hardware lacks the capability to distinguish whether PRI occurs at stage 1
or stage 2. This limitation may require software-based page table walking
to resolve. Since no in-tree IOMMU driver currently supports this
functionality, it is disallowed. For more details, refer to the related
discussion at [1].

[1] https://lore.kernel.org/linux-iommu/bd1655c6-8b2f-4cfa-adb1-badc00d01811@intel.com/

Link: https://patch.msgid.link/r/20250226104012.82079-1-yi.l.liu@intel.com
Suggested-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

diff --git a/drivers/iommu/iommufd/hw_pagetable.c b/drivers/iommu/iommufd/hw_pagetable.c
index 7de6e914232e71d8297aed8575bb0261249b5d28..268315b1d8bc0d3732e90d64cc3c783dc9fb3065 100644 (file)
--- a/drivers/iommu/iommufd/hw_pagetable.c
+++ b/drivers/iommu/iommufd/hw_pagetable.c
@@ -126,6 +126,9 @@ iommufd_hwpt_paging_alloc(struct iommufd_ctx *ictx, struct iommufd_ioas *ioas,
        if ((flags & IOMMU_HWPT_ALLOC_DIRTY_TRACKING) &&
            !device_iommu_capable(idev->dev, IOMMU_CAP_DIRTY_TRACKING))
                return ERR_PTR(-EOPNOTSUPP);
+       if ((flags & IOMMU_HWPT_FAULT_ID_VALID) &&
+           (flags & IOMMU_HWPT_ALLOC_NEST_PARENT))
+               return ERR_PTR(-EOPNOTSUPP);
 
        hwpt_paging = __iommufd_object_alloc(
                ictx, hwpt_paging, IOMMUFD_OBJ_HWPT_PAGING, common.obj);

diff --git a/tools/testing/selftests/iommu/iommufd.c b/tools/testing/selftests/iommu/iommufd.c
index a1b2b657999dcc76551b8aed53041478138a0dcd..618c03bb6509bf56d402246c359536b5ba82f557 100644 (file)
--- a/tools/testing/selftests/iommu/iommufd.c
+++ b/tools/testing/selftests/iommu/iommufd.c
@@ -439,6 +439,10 @@ TEST_F(iommufd_ioas, alloc_hwpt_nested)
                                    &test_hwpt_id);
                test_err_hwpt_alloc(EINVAL, self->device_id, self->device_id, 0,
                                    &test_hwpt_id);
+               test_err_hwpt_alloc(EOPNOTSUPP, self->device_id, self->ioas_id,
+                                   IOMMU_HWPT_ALLOC_NEST_PARENT |
+                                               IOMMU_HWPT_FAULT_ID_VALID,
+                                   &test_hwpt_id);
 
                test_cmd_hwpt_alloc(self->device_id, self->ioas_id,
                                    IOMMU_HWPT_ALLOC_NEST_PARENT,