iommufd: Set domain->iommufd_hwpt in all hwpt->domain allocators

Setting domain->iommufd_hwpt in iommufd_hwpt_alloc() only covers the HWPT
allocations from user space, but not for an auto domain. This resulted in
a NULL pointer access in the auto domain pathway:
 Unable to handle kernel NULL pointer dereference at
 	virtual address 0000000000000008
 pc : iommufd_sw_msi+0x54/0x2b0
 lr : iommufd_sw_msi+0x40/0x2b0
 Call trace:
  iommufd_sw_msi+0x54/0x2b0 (P)
  iommu_dma_prepare_msi+0x64/0xa8
  its_irq_domain_alloc+0xf0/0x2c0
  irq_domain_alloc_irqs_parent+0x2c/0xa8
  msi_domain_alloc+0xa0/0x1a8

Since iommufd_sw_msi() requires to access the domain->iommufd_hwpt, it is
better to set that explicitly prior to calling iommu_domain_set_sw_msi().

Fixes: 748706d ("iommu: Turn fault_data to iommufd private pointer")
Link: https://patch.msgid.link/r/20250305211800.229465-1-nicolinc@nvidia.com
Reported-by: Ankit Agrawal <ankita@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Ankit Agrawal <ankita@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/iommu/iommufd/hw_pagetable.c

@@ -159,6 +159,7 @@ iommufd_hwpt_paging_alloc(struct iommufd_ctx *ictx, struct iommufd_ioas *ioas,
 			goto out_abort;
 		}
 	}
+	hwpt->domain->iommufd_hwpt = hwpt;
 	iommu_domain_set_sw_msi(hwpt->domain, iommufd_sw_msi);
 
 	/*
@@ -255,6 +256,7 @@ iommufd_hwpt_nested_alloc(struct iommufd_ctx *ictx,
 		goto out_abort;
 	}
 	hwpt->domain->owner = ops;
+	hwpt->domain->iommufd_hwpt = hwpt;
 	iommu_domain_set_sw_msi(hwpt->domain, iommufd_sw_msi);
 
 	if (WARN_ON_ONCE(hwpt->domain->type != IOMMU_DOMAIN_NESTED)) {
@@ -311,6 +313,7 @@ iommufd_viommu_alloc_hwpt_nested(struct iommufd_viommu *viommu, u32 flags,
 		hwpt->domain = NULL;
 		goto out_abort;
 	}
+	hwpt->domain->iommufd_hwpt = hwpt;
 	hwpt->domain->owner = viommu->iommu_dev->ops;
 	iommu_domain_set_sw_msi(hwpt->domain, iommufd_sw_msi);
 
@@ -415,7 +418,6 @@ int iommufd_hwpt_alloc(struct iommufd_ucmd *ucmd)
 		refcount_inc(&fault->obj.users);
 		iommufd_put_object(ucmd->ictx, &fault->obj);
 	}
-	hwpt->domain->iommufd_hwpt = hwpt;
 
 	cmd->out_hwpt_id = hwpt->obj.id;
 	rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));