exec: small changes to flatview_do_translate

Prepare for extracting the IOMMU part to a separate function.  Mostly
cosmetic; the only semantic change is that, if there is more than one
cascaded IOMMU and the second one fails to translate, *plen_out is now
adjusted according to the page mask of the first IOMMU.

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

exec.c

@@ -476,6 +476,7 @@ address_space_translate_internal(AddressSpaceDispatch *d, hwaddr addr, hwaddr *x
  *            would tell. It can be @NULL if we don't care about it.
  * @is_write: whether the translation operation is for write
  * @is_mmio: whether this can be MMIO, set true if it can
+ * @target_as: the address space targeted by the IOMMU
  *
  * This function is called from RCU critical section
  */
@@ -495,50 +496,44 @@ static MemoryRegionSection flatview_do_translate(FlatView *fv,
     hwaddr page_mask = (hwaddr)(-1);
     hwaddr plen = (hwaddr)(-1);
 
-    if (plen_out) {
-        plen = *plen_out;
+    if (!plen_out) {
+        plen_out = &plen;
     }
 
     for (;;) {
         section = address_space_translate_internal(
-                flatview_to_dispatch(fv), addr, &addr,
-                &plen, is_mmio);
+                flatview_to_dispatch(fv), addr, xlat,
+                plen_out, is_mmio);
 
         iommu_mr = memory_region_get_iommu(section->mr);
         if (!iommu_mr) {
             break;
         }
         imrc = memory_region_get_iommu_class_nocheck(iommu_mr);
 
+        addr = *xlat;
         iotlb = imrc->translate(iommu_mr, addr, is_write ?
                                 IOMMU_WO : IOMMU_RO);
-        addr = ((iotlb.translated_addr & ~iotlb.addr_mask)
-                | (addr & iotlb.addr_mask));
-        page_mask &= iotlb.addr_mask;
-        plen = MIN(plen, (addr | iotlb.addr_mask) - addr + 1);
         if (!(iotlb.perm & (1 << is_write))) {
             goto translate_fail;
         }
 
+        addr = ((iotlb.translated_addr & ~iotlb.addr_mask)
+                | (addr & iotlb.addr_mask));
+        page_mask &= iotlb.addr_mask;
+        *plen_out = MIN(*plen_out, (addr | iotlb.addr_mask) - addr + 1);
         fv = address_space_to_flatview(iotlb.target_as);
         *target_as = iotlb.target_as;
     }
 
-    *xlat = addr;
-
-    if (page_mask == (hwaddr)(-1)) {
-        /* Not behind an IOMMU, use default page size. */
-        page_mask = ~TARGET_PAGE_MASK;
-    }
-
     if (page_mask_out) {
+        if (page_mask == (hwaddr)(-1)) {
+            /* Not behind an IOMMU, use default page size. */
+            page_mask = ~TARGET_PAGE_MASK;
+        }
         *page_mask_out = page_mask;
     }
 
-    if (plen_out) {
-        *plen_out = plen;
-    }
-
     return *section;
 
 translate_fail: