intel-iommu: Fix use after release during device attach

Obtain the new pgd pointer before releasing the page containing this
value.

Cc: stable@kernel.org
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: NSheng Yang <sheng@linux.intel.com>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>

drivers/pci/intel-iommu.c

@@ -3627,9 +3627,9 @@ 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 *)
 				phys_to_virt(dma_pte_addr(pte));
+			free_pgtable_page(pte);
 		}
 		dmar_domain->agaw--;
 	}