VT-d: don't crash when PTE bits 52 and up are non-zero

This can (and will) be legitimately the case when sharing page tables
with EPT (more of a problem before p2m_access_rwx became zero, but
still possible even now when other than that is the default for a
guest), leading to an unconditional crash (in print_vtd_entries())
when a DMA remapping fault occurs.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Regarding the release, if the changes to iommu.c are deemed too
extensive, then _I think_ they could be split off (that code ought to
come into play only when not sharing page tables between VT-d and EPT,
and VT-d code never sets the offending bits to non-zero values afaict).

--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -258,8 +258,7 @@ static u64 addr_to_dma_page_maddr(struct
     struct dma_pte *parent, *pte = NULL;
     int level = agaw_to_level(hd->arch.agaw);
     int offset;
-    u64 pte_maddr = 0, maddr;
-    u64 *vaddr = NULL;
+    u64 pte_maddr = 0;
 
     addr &= (((u64)1) << addr_width) - 1;
     ASSERT(spin_is_locked(&hd->arch.mapping_lock));
@@ -281,19 +280,19 @@ static u64 addr_to_dma_page_maddr(struct
         offset = address_level_offset(addr, level);
         pte = &parent[offset];
 
-        if ( dma_pte_addr(*pte) == 0 )
+        pte_maddr = dma_pte_addr(*pte);
+        if ( !pte_maddr )
         {
             if ( !alloc )
                 break;
 
             pdev = pci_get_pdev_by_domain(domain, -1, -1, -1);
             drhd = acpi_find_matched_drhd_unit(pdev);
-            maddr = alloc_pgtable_maddr(drhd, 1);
-            if ( !maddr )
+            pte_maddr = alloc_pgtable_maddr(drhd, 1);
+            if ( !pte_maddr )
                 break;
 
-            dma_set_pte_addr(*pte, maddr);
-            vaddr = map_vtd_domain_page(maddr);
+            dma_set_pte_addr(*pte, pte_maddr);
 
             /*
              * high level table always sets r/w, last level
@@ -303,21 +302,12 @@ static u64 addr_to_dma_page_maddr(struct
             dma_set_pte_writable(*pte);
             iommu_flush_cache_entry(pte, sizeof(struct dma_pte));
         }
-        else
-        {
-            vaddr = map_vtd_domain_page(pte->val);
-        }
 
         if ( level == 2 )
-        {
-            pte_maddr = pte->val & PAGE_MASK_4K;
-            unmap_vtd_domain_page(vaddr);
             break;
-        }
 
         unmap_vtd_domain_page(parent);
-        parent = (struct dma_pte *)vaddr;
-        vaddr = NULL;
+        parent = map_vtd_domain_page(pte_maddr);
         level--;
     }
 
@@ -2449,7 +2439,7 @@ static void vtd_dump_p2m_table_level(pad
             printk("%*sgfn: %08lx mfn: %08lx\n",
                    indent, "",
                    (unsigned long)(address >> PAGE_SHIFT_4K),
-                   (unsigned long)(pte->val >> PAGE_SHIFT_4K));
+                   (unsigned long)(dma_pte_addr(*pte) >> PAGE_SHIFT_4K));
     }
 
     unmap_vtd_domain_page(pt_vaddr);
--- a/xen/drivers/passthrough/vtd/iommu.h
+++ b/xen/drivers/passthrough/vtd/iommu.h
@@ -276,7 +276,7 @@ struct dma_pte {
 #define dma_set_pte_snp(p)  do {(p).val |= DMA_PTE_SNP;} while(0)
 #define dma_set_pte_prot(p, prot) \
             do {(p).val = ((p).val & ~3) | ((prot) & 3); } while (0)
-#define dma_pte_addr(p) ((p).val & PAGE_MASK_4K)
+#define dma_pte_addr(p) ((p).val & PADDR_MASK & PAGE_MASK_4K)
 #define dma_set_pte_addr(p, addr) do {\
             (p).val |= ((addr) & PAGE_MASK_4K); } while (0)
 #define dma_pte_present(p) (((p).val & 3) != 0)
--- a/xen/drivers/passthrough/vtd/utils.c
+++ b/xen/drivers/passthrough/vtd/utils.c
@@ -170,16 +170,16 @@ void print_vtd_entries(struct iommu *iom
         l_index = get_level_index(gmfn, level);
         printk("    l%d_index = %x\n", level, l_index);
 
-        pte.val = val = l[l_index];
+        pte.val = l[l_index];
         unmap_vtd_domain_page(l);
-        printk("    l%d[%x] = %"PRIx64"\n", level, l_index, val);
+        printk("    l%d[%x] = %"PRIx64"\n", level, l_index, pte.val);
 
-        pte.val = val;
         if ( !dma_pte_present(pte) )
         {
             printk("    l%d[%x] not present\n", level, l_index);
             break;
         }
+        val = dma_pte_addr(pte);
     } while ( --level );
 }