x86: use 2M superpages for text/data/bss mappings

This balloons the size of Xen in memory from 4.4MB to 8MB, because of the
required alignment adjustments.

However
 * All mappings are 2M superpages.
 * .text (and .init at boot) are the only sections marked executable.
 * .text and .rodata are marked read-only.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/setup.c

@@ -920,14 +920,46 @@ void __init noreturn __start_xen(unsigned long mbi_p)
 
             /* The only data mappings to be relocated are in the Xen area. */
             pl2e = __va(__pa(l2_xenmap));
+            /*
+             * Undo the temporary-hooking of the l1_identmap.  __2M_text_start
+             * is contained in this PTE.
+             */
             *pl2e++ = l2e_from_pfn(xen_phys_start >> PAGE_SHIFT,
-                                   PAGE_HYPERVISOR_RWX | _PAGE_PSE);
+                                   PAGE_HYPERVISOR_RX | _PAGE_PSE);
             for ( i = 1; i < L2_PAGETABLE_ENTRIES; i++, pl2e++ )
             {
+                unsigned int flags;
+
                 if ( !(l2e_get_flags(*pl2e) & _PAGE_PRESENT) )
                     continue;
-                *pl2e = l2e_from_intpte(l2e_get_intpte(*pl2e) +
-                                        xen_phys_start);
+
+                if ( i < l2_table_offset((unsigned long)&__2M_text_end) )
+                {
+                    flags = PAGE_HYPERVISOR_RX | _PAGE_PSE;
+                }
+                else if ( i >= l2_table_offset((unsigned long)&__2M_rodata_start) &&
+                          i <  l2_table_offset((unsigned long)&__2M_rodata_end) )
+                {
+                    flags = PAGE_HYPERVISOR_RO | _PAGE_PSE;
+                }
+                else if ( i >= l2_table_offset((unsigned long)&__2M_init_start) &&
+                          i <  l2_table_offset((unsigned long)&__2M_init_end) )
+                {
+                    flags = PAGE_HYPERVISOR_RWX | _PAGE_PSE;
+                }
+                else if ( (i >= l2_table_offset((unsigned long)&__2M_rwdata_start) &&
+                           i <  l2_table_offset((unsigned long)&__2M_rwdata_end)) )
+                {
+                    flags = PAGE_HYPERVISOR_RW | _PAGE_PSE;
+                }
+                else
+                {
+                    *pl2e = l2e_empty();
+                    continue;
+                }
+
+                *pl2e = l2e_from_paddr(
+                    l2e_get_paddr(*pl2e) + xen_phys_start, flags);
             }
 
             /* Re-sync the stack and then switch to relocated pagetables. */

xen/arch/x86/xen.lds.S

@@ -38,6 +38,9 @@ SECTIONS
   . = __XEN_VIRT_START;
   __image_base__ = .;
 #endif
+
+  __2M_text_start = .;         /* Start of 2M superpages, mapped RX. */
+
   . = __XEN_VIRT_START + MB(1);
   _start = .;
   .text : {
@@ -50,6 +53,10 @@ SECTIONS
        _etext = .;             /* End of text section */
   } :text = 0x9090
 
+  . = ALIGN(MB(2));
+  __2M_text_end = .;
+
+  __2M_rodata_start = .;       /* Start of 2M superpages, mapped RO. */
   .rodata : {
        /* Bug frames table */
        . = ALIGN(4);
@@ -74,6 +81,10 @@ SECTIONS
 #endif
   } :text
 
+  . = ALIGN(MB(2));
+  __2M_rodata_end = .;
+
+  __2M_init_start = .;         /* Start of 2M superpages, mapped RWX (boot only). */
   . = ALIGN(PAGE_SIZE);             /* Init code and data */
   __init_begin = .;
   .init.text : {
@@ -137,6 +148,10 @@ SECTIONS
   . = ALIGN(PAGE_SIZE);
   __init_end = .;
 
+  . = ALIGN(MB(2));
+  __2M_init_end = .;
+
+  __2M_rwdata_start = .;       /* Start of 2M superpages, mapped RW. */
   . = ALIGN(SMP_CACHE_BYTES);
   .data.read_mostly : {
        /* Exception table */
@@ -185,6 +200,9 @@ SECTIONS
   } :text
   _end = . ;
 
+  . = ALIGN(MB(2));
+  __2M_rwdata_end = .;
+
 #ifdef EFI
   . = ALIGN(4);
   .reloc : {
@@ -231,4 +249,13 @@ ASSERT(__image_base__ > XEN_VIRT_START ||
 ASSERT(kexec_reloc_size - kexec_reloc <= PAGE_SIZE, "kexec_reloc is too large")
 #endif
 
+ASSERT(IS_ALIGNED(__2M_text_start,   MB(2)), "__2M_text_start misaligned")
+ASSERT(IS_ALIGNED(__2M_text_end,     MB(2)), "__2M_text_end misaligned")
+ASSERT(IS_ALIGNED(__2M_rodata_start, MB(2)), "__2M_rodata_start misaligned")
+ASSERT(IS_ALIGNED(__2M_rodata_end,   MB(2)), "__2M_rodata_end misaligned")
+ASSERT(IS_ALIGNED(__2M_init_start,   MB(2)), "__2M_init_start misaligned")
+ASSERT(IS_ALIGNED(__2M_init_end,     MB(2)), "__2M_init_end misaligned")
+ASSERT(IS_ALIGNED(__2M_rwdata_start, MB(2)), "__2M_rwdata_start misaligned")
+ASSERT(IS_ALIGNED(__2M_rwdata_end,   MB(2)), "__2M_rwdata_end misaligned")
+
 ASSERT(IS_ALIGNED(cpu0_stack, STACK_SIZE), "cpu0_stack misaligned")

xen/include/asm-x86/setup.h

@@ -4,6 +4,11 @@
 #include <xen/multiboot.h>
 #include <asm/numa.h>
 
+extern const char __2M_text_start[], __2M_text_end[];
+extern const char __2M_rodata_start[], __2M_rodata_end[];
+extern char __2M_init_start[], __2M_init_end[];
+extern char __2M_rwdata_start[], __2M_rwdata_end[];
+
 extern unsigned long xenheap_initial_phys_start;
 
 void early_cpu_init(void);