iommu/vt-d: Remove BUG_ON when domain->pgd is NULL

When performing domain_context_mapping or getting dma_pte of a pfn, the
availability of the domain page table directory is ensured. Therefore,
the domain->pgd checkings are unnecessary.

Signed-off-by: Tina Zhang <tina.zhang@intel.com>
Link: https://lore.kernel.org/r/20230406065944.2773296-5-tina.zhang@intel.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Author: TinaZhangZW

drivers/iommu/intel/iommu.c

@@ -915,8 +915,6 @@ static struct dma_pte *pfn_to_dma_pte(struct dmar_domain *domain,
 	int level = agaw_to_level(domain->agaw);
 	int offset;
 
-	BUG_ON(!domain->pgd);
-
 	if (!domain_pfn_supported(domain, pfn))
 		/* Address beyond IOMMU's addressing capabilities. */
 		return NULL;
@@ -1910,8 +1908,6 @@ static int domain_context_mapping_one(struct dmar_domain *domain,
 	pr_debug("Set context mapping for %02x:%02x.%d\n",
 		bus, PCI_SLOT(devfn), PCI_FUNC(devfn));
 
-	BUG_ON(!domain->pgd);
-
 	spin_lock(&iommu->lock);
 	ret = -ENOMEM;
 	context = iommu_context_addr(iommu, bus, devfn, 1);