x86: don't blindly create L3 tables for the direct map

Now that the direct map area can extend all the way up to almost the
end of address space, this is wasteful.

Also fold two almost redundant messages in SRAT parsing into one.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Tested-by: Malcolm Crossley <malcolm.crossley@xxxxxxxxxx>

--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -137,7 +137,7 @@ l1_pgentry_t __attribute__ ((__section__
 #define PTE_UPDATE_WITH_CMPXCHG
 #endif
 
-bool_t __read_mostly mem_hotplug = 0;
+paddr_t __read_mostly mem_hotplug;
 
 /* Private domain structs for DOMID_XEN and DOMID_IO. */
 struct domain *dom_xen, *dom_io, *dom_cow;
--- a/xen/arch/x86/srat.c
+++ b/xen/arch/x86/srat.c
@@ -113,6 +113,7 @@ static __init void bad_srat(void)
 		apicid_to_node[i] = NUMA_NO_NODE;
 	for (i = 0; i < ARRAY_SIZE(pxm2node); i++)
 		pxm2node[i] = NUMA_NO_NODE;
+	mem_hotplug = 0;
 }
 
 /*
@@ -257,13 +258,6 @@ acpi_numa_memory_affinity_init(struct ac
 		return;
 	}
 	/* It is fine to add this area to the nodes data it will be used later*/
-	if (ma->flags & ACPI_SRAT_MEM_HOT_PLUGGABLE)
-	{
-		printk(KERN_INFO "SRAT: hot plug zone found %"PRIx64" - %"PRIx64" \n",
-				start, end);
-		mem_hotplug = 1;
-	}
-
 	i = conflicting_memblks(start, end);
 	if (i == node) {
 		printk(KERN_WARNING
@@ -287,8 +281,11 @@ acpi_numa_memory_affinity_init(struct ac
 		if (nd->end < end)
 			nd->end = end;
 	}
-	printk(KERN_INFO "SRAT: Node %u PXM %u %"PRIx64"-%"PRIx64"\n", node, pxm,
-	       start, end);
+	if ((ma->flags & ACPI_SRAT_MEM_HOT_PLUGGABLE) && end > mem_hotplug)
+		mem_hotplug = end;
+	printk(KERN_INFO "SRAT: Node %u PXM %u %"PRIx64"-%"PRIx64"%s\n",
+	       node, pxm, start, end,
+	       ma->flags & ACPI_SRAT_MEM_HOT_PLUGGABLE ? " (hotplug)" : "");
 
 	node_memblk_range[num_node_memblks].start = start;
 	node_memblk_range[num_node_memblks].end = end;
--- a/xen/arch/x86/x86_64/mm.c
+++ b/xen/arch/x86/x86_64/mm.c
@@ -559,25 +559,20 @@ void __init paging_init(void)
      * We setup the L3s for 1:1 mapping if host support memory hotplug
      * to avoid sync the 1:1 mapping on page fault handler
      */
-    if ( mem_hotplug )
+    for ( va = DIRECTMAP_VIRT_START;
+          va < DIRECTMAP_VIRT_END && (void *)va < __va(mem_hotplug);
+          va += (1UL << L4_PAGETABLE_SHIFT) )
     {
-        unsigned long va;
-
-        for ( va = DIRECTMAP_VIRT_START;
-              va < DIRECTMAP_VIRT_END;
-              va += (1UL << L4_PAGETABLE_SHIFT) )
+        if ( !(l4e_get_flags(idle_pg_table[l4_table_offset(va)]) &
+              _PAGE_PRESENT) )
         {
-            if ( !(l4e_get_flags(idle_pg_table[l4_table_offset(va)]) &
-                  _PAGE_PRESENT) )
-            {
-                l3_pg = alloc_domheap_page(NULL, 0);
-                if ( !l3_pg )
-                    goto nomem;
-                l3_ro_mpt = page_to_virt(l3_pg);
-                clear_page(l3_ro_mpt);
-                l4e_write(&idle_pg_table[l4_table_offset(va)],
-                  l4e_from_page(l3_pg, __PAGE_HYPERVISOR));
-            }
+            l3_pg = alloc_domheap_page(NULL, 0);
+            if ( !l3_pg )
+                goto nomem;
+            l3_ro_mpt = page_to_virt(l3_pg);
+            clear_page(l3_ro_mpt);
+            l4e_write(&idle_pg_table[l4_table_offset(va)],
+                      l4e_from_page(l3_pg, __PAGE_HYPERVISOR));
         }
     }
 
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -399,7 +399,7 @@ static inline int get_page_and_type(stru
 int check_descriptor(const struct domain *, struct desc_struct *d);
 
 extern bool_t opt_allow_superpage;
-extern bool_t mem_hotplug;
+extern paddr_t mem_hotplug;
 
 /******************************************************************************
  * With shadow pagetables, the different kinds of address start