intel-iommu: Fix reference by physical address in intel_iommu_attach_device()

Commit a99c47a2 "intel-iommu: errors with smaller iommu widths" replace the
dmar_domain->pgd with the first entry of page table when iommu's supported
width is smaller than dmar_domain's. But it use physical address directly
for new dmar_domain->pgd...

This result in KVM oops with VT-d on some machines.
Reported-by: Allen Kay <allen.m.kay@intel.com>
Cc: Tom Lyon <pugs@cisco.com>
Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/pci/intel-iommu.c

@@ -3603,7 +3603,8 @@ static int intel_iommu_attach_device(struct iommu_domain *domain,
 		pte = dmar_domain->pgd;
 		if (dma_pte_present(pte)) {
 			free_pgtable_page(dmar_domain->pgd);
-			dmar_domain->pgd = (struct dma_pte *)dma_pte_addr(pte);
+			dmar_domain->pgd = (struct dma_pte *)
+				phys_to_virt(dma_pte_addr(pte));
 		}
 		dmar_domain->agaw--;
 	}