In preparation for reactivating the presently dead 2M page path of the
function, also deal with the case of replacing an L1 page table all in
one go.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
v2: Split from previous bigger patch.

--- a/xen/arch/x86/mm/shadow/hvm.c
+++ b/xen/arch/x86/mm/shadow/hvm.c
@@ -847,14 +847,9 @@ static void cf_check sh_unshadow_for_p2m
      * scheme, that's OK, but otherwise they must be unshadowed.
      */
     case 2:
-        if ( !(oflags & _PAGE_PSE) )
-            break;
-
-        ASSERT(!p2m_is_grant(p2mt));
-
         {
             unsigned int i;
-            l1_pgentry_t *npte = NULL;
+            l1_pgentry_t *npte = NULL, *opte = NULL;
 
             /* If we're replacing a superpage with a normal L1 page, map it */
             if ( (l1e_get_flags(new) & _PAGE_PRESENT) &&
@@ -862,24 +857,39 @@ static void cf_check sh_unshadow_for_p2m
                  mfn_valid(nmfn) )
                 npte = map_domain_page(nmfn);
 
+            /* If we're replacing a normal L1 page, map it as well. */
+            if ( !(oflags & _PAGE_PSE) )
+                opte = map_domain_page(omfn);
+
             gfn &= ~(L1_PAGETABLE_ENTRIES - 1);
 
             for ( i = 0; i < L1_PAGETABLE_ENTRIES; i++ )
             {
-                if ( !npte ||
-                     !(l1e_get_flags(npte[i]) & _PAGE_PRESENT) ||
-                     !mfn_eq(l1e_get_mfn(npte[i]), omfn) )
+                if ( opte )
+                {
+                    if ( !(l1e_get_flags(opte[i]) & _PAGE_PRESENT) )
+                        continue;
+                    omfn = l1e_get_mfn(opte[i]);
+                }
+
+                if ( npte )
+                    nmfn = l1e_get_flags(npte[i]) & _PAGE_PRESENT
+                           ? l1e_get_mfn(npte[i]) : INVALID_MFN;
+
+                if ( !mfn_eq(nmfn, omfn) )
                 {
                     /* This GFN->MFN mapping has gone away */
                     sh_remove_all_shadows_and_parents(d, omfn);
                     if ( sh_remove_all_mappings(d, omfn, _gfn(gfn + i)) )
                         flush = true;
                 }
+
                 omfn = mfn_add(omfn, 1);
+                nmfn = mfn_add(nmfn, 1);
             }
 
-            if ( npte )
-                unmap_domain_page(npte);
+            unmap_domain_page(opte);
+            unmap_domain_page(npte);
         }
 
         break;