[v10,11/13] x86: make Xen early boot code relocatable
diff mbox

Message ID 1480511059-14062-12-git-send-email-daniel.kiper@oracle.com
State New, archived
Headers show

Commit Message

Daniel Kiper Nov. 30, 2016, 1:04 p.m. UTC
Every multiboot protocol (regardless of version) compatible image must
specify its load address (in ELF or multiboot header). Multiboot protocol
compatible loader have to load image at specified address. However, there
is no guarantee that the requested memory region (in case of Xen it starts
at 2 MiB and ends at ~5 MiB) where image should be loaded initially is a RAM
and it is free (legacy BIOS platforms are merciful for Xen but I found at
least one EFI platform on which Xen load address conflicts with EFI boot
services; it is Dell PowerEdge R820 with latest firmware). To cope with that
problem we must make Xen early boot code relocatable and help boot loader to
relocate image in proper way by suggesting, not requesting specific load
addresses as it is right now, allowed address ranges. This patch does former.
It does not add multiboot2 protocol interface which is done in "x86: add
multiboot2 protocol support for relocatable images" patch.

This patch changes following things:
  - %esi and %r15d registers are used as a storage for Xen image load base
    address (%r15d shortly because %rsi is used for EFI SystemTable address
    in 64-bit code); both registers are (%esi is mostly) unused in early
    boot code and preserved during C functions calls (%esi in 32-bit code
    and %r15d in 64-bit code),
  - %fs is used as base for Xen data relative addressing in 32-bit code
    if it is possible; %esi is used for that thing during error printing
    because it is not always possible to properly and efficiently
    initialize %fs.

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
---
v8 - suggestions/fixes:
   - use shld instead of mov and shr in BOOT_FS segment
     descriptor base address initialization
     (suggested by Jan Beulich),
   - simplify code updating frame addresses in page tables
     (suggested by Jan Beulich),
   - print Xen image base addresses using "%#lx" format
     (suggested by Jan Beulich),
   - improve comments
     (suggested by Jan Beulich).

v6 - suggestions/fixes:
   - leave static mapping of first
     16 MiB in l2_identmap as is
     (suggested by Jan Beulich),
   - use xen_phys_start instead of xen_img_load_base_addr
     (suggested by Daniel Kiper and Jan Beulich),
   - simplify BOOT_FS segment descriptor
     base address initialization
     (suggested by Jan Beulich),
   - fix BOOT_FS segment limit
     (suggested by Jan Beulich),
   - do not rename sym_phys in this patch
     (suggested by Jan Beulich),
   - rename esi_offset/fs_offset to
     sym_esi/sym_fs respectively
     (suggested by Jan Beulich),
   - use add instead of lea in assembly
     error printing code
     (suggested by Jan Beulich),
   - improve comments
     (suggested by Jan Beulich),
   - improve commit message
     (suggested by Jan Beulich),
   - various minor cleanups and fixes
     (suggested by Jan Beulich).

v4 - suggestions/fixes:
   - do not relocate Xen image if boot loader did work for us
     (suggested by Andrew Cooper and Jan Beulich),
   - initialize xen_img_load_base_addr in EFI boot code too,
   - properly initialize trampoline_xen_phys_start,
   - calculate Xen image load base address in
     x86_64 code ourselves,
     (suggested by Jan Beulich),
   - change how and when Xen image base address is printed,
   - use %fs instead of %esi for relative addressing
     (suggested by Andrew Cooper and Jan Beulich),
   - create esi_offset and fs_offset() macros in assembly,
   - calculate <final-exec-addr> mkelf32 argument automatically,
   - optimize and cleanup code,
   - improve comments,
   - improve commit message.

v3 - suggestions/fixes:
   - improve segment registers initialization
     (suggested by Jan Beulich),
   - simplify Xen image load base address calculation
     (suggested by Jan Beulich),
   - use %esi and %r15d instead of %ebp to store
     Xen image load base address,
   - use %esi instead of %fs for relative addressing;
     this way we get shorter and simpler code,
   - rename some variables and constants
     (suggested by Jan Beulich),
   - improve comments
     (suggested by Konrad Rzeszutek Wilk),
   - improve commit message
     (suggested by Jan Beulich).
---
 xen/arch/x86/boot/head.S          |  160 +++++++++++++++++++++++++++++--------
 xen/arch/x86/boot/trampoline.S    |    5 ++
 xen/arch/x86/boot/x86_64.S        |   21 +++--
 xen/arch/x86/setup.c              |   14 ++--
 xen/arch/x86/x86_64/asm-offsets.c |    3 +
 xen/include/asm-x86/page.h        |    2 +-
 6 files changed, 155 insertions(+), 50 deletions(-)

Patch
diff mbox

diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index a7bc467..d992a95 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -13,12 +13,15 @@ 
         .code32
 
 #define sym_phys(sym)     ((sym) - __XEN_VIRT_START)
+#define sym_esi(sym)      sym_phys(sym)(%esi)
+#define sym_fs(sym)       %fs:sym_phys(sym)
 
 #define BOOT_CS32        0x0008
 #define BOOT_CS64        0x0010
 #define BOOT_DS          0x0018
 #define BOOT_PSEUDORM_CS 0x0020
 #define BOOT_PSEUDORM_DS 0x0028
+#define BOOT_FS          0x0030
 
 #define MB2_HT(name)      (MULTIBOOT2_HEADER_TAG_##name)
 #define MB2_TT(name)      (MULTIBOOT2_TAG_TYPE_##name)
@@ -105,7 +108,8 @@  multiboot2_header_start:
 
         .word   0
 gdt_boot_descr:
-        .word   6*8-1
+        .word   7*8-1
+gdt_boot_base:
         .long   sym_phys(trampoline_gdt)
         .long   0 /* Needed for 64-bit lgdt */
 
@@ -126,27 +130,27 @@  efi_platform:
         .section .init.text, "ax", @progbits
 
 bad_cpu:
-        mov     $(sym_phys(.Lbad_cpu_msg)),%esi # Error message
+        add     $sym_phys(.Lbad_cpu_msg),%esi   # Error message
         jmp     .Lget_vtb
 not_multiboot:
-        mov     $(sym_phys(.Lbad_ldr_msg)),%esi # Error message
+        add     $sym_phys(.Lbad_ldr_msg),%esi   # Error message
         jmp     .Lget_vtb
 .Lmb2_no_st:
-        mov     $(sym_phys(.Lbad_ldr_nst)),%esi # Error message
+        add     $sym_phys(.Lbad_ldr_nst),%esi   # Error message
         jmp     .Lget_vtb
 .Lmb2_no_ih:
-        mov     $(sym_phys(.Lbad_ldr_nih)),%esi # Error message
+        add     $sym_phys(.Lbad_ldr_nih),%esi   # Error message
         jmp     .Lget_vtb
 .Lmb2_no_bs:
-        mov     $(sym_phys(.Lbad_ldr_nbs)),%esi # Error message
+        add     $sym_phys(.Lbad_ldr_nbs),%esi   # Error message
         xor     %edi,%edi                       # No VGA text buffer
         jmp     .Lsend_chr
 .Lmb2_efi_ia_32:
-        mov     $(sym_phys(.Lbad_efi_msg)),%esi # Error message
+        add     $sym_phys(.Lbad_efi_msg),%esi   # Error message
         xor     %edi,%edi                       # No VGA text buffer
         jmp     .Lsend_chr
 .Lget_vtb:
-        mov     sym_phys(vga_text_buffer),%edi
+        mov     sym_esi(vga_text_buffer),%edi
 .Lsend_chr:
         mov     (%esi),%bl
         test    %bl,%bl        # Terminate on '\0' sentinel
@@ -175,6 +179,9 @@  __efi64_start:
         /* VGA is not available on EFI platforms. */
         movl   $0,vga_text_buffer(%rip)
 
+        /* Load Xen image load base address. */
+        lea     __image_base__(%rip),%r15d
+
         /* Check for Multiboot2 bootloader. */
         cmp     $MULTIBOOT2_BOOTLOADER_MAGIC,%eax
         je      .Lefi_multiboot2_proto
@@ -300,6 +307,9 @@  run_bs:
 
         pop     %rax
 
+        /* Store Xen image load base address in place accessible for 32-bit code. */
+        mov     %r15d,%esi
+
         /* Jump to trampoline_setup after switching CPU to x86_32 mode. */
         lea     trampoline_setup(%rip),%edi
 
@@ -307,6 +317,7 @@  x86_32_switch:
         cli
 
         /* Initialize GDTR. */
+        add     %esi,gdt_boot_base(%rip)
         lgdt    gdt_boot_descr(%rip)
 
         /* Reload code selector. */
@@ -342,12 +353,8 @@  __start:
         cld
         cli
 
-        /* Initialise GDT and basic data segments. */
-        lgdt    %cs:sym_phys(gdt_boot_descr)
-        mov     $BOOT_DS,%ecx
-        mov     %ecx,%ds
-        mov     %ecx,%es
-        mov     %ecx,%ss
+        /* Load default Xen image load base address. */
+        mov     $sym_phys(__image_base__),%esi
 
         /* Bootloaders may set multiboot{1,2}.mem_lower to a nonzero value. */
         xor     %edx,%edx
@@ -404,6 +411,25 @@  __start:
         jmp     .Lmb2_tsize
 
 trampoline_bios_setup:
+        /*
+         * Called on legacy BIOS platforms only.
+         *
+         * Initialize GDTR and basic data segments.
+         */
+        add     %esi,sym_esi(gdt_boot_base)
+        lgdt    sym_esi(gdt_boot_descr)
+
+        mov     $BOOT_DS,%ecx
+        mov     %ecx,%ds
+        mov     %ecx,%es
+        mov     %ecx,%ss
+        /* %esp is initialized later. */
+
+        /* Load null descriptor to unused segment registers. */
+        xor     %ecx,%ecx
+        mov     %ecx,%fs
+        mov     %ecx,%gs
+
         /* Set up trampoline segment 64k below EBDA */
         movzwl  0x40e,%ecx          /* EBDA segment */
         cmp     $0xa000,%ecx        /* sanity check (high) */
@@ -431,32 +457,64 @@  trampoline_bios_setup:
         xor     %cl, %cl
 
 trampoline_setup:
+        /*
+         * Called on legacy BIOS and EFI platforms.
+         *
+         * Initialize 0-15 bits of BOOT_FS segment descriptor base address.
+         */
+        mov     %si,BOOT_FS+2+sym_esi(trampoline_gdt)
+
+        /* Initialize 16-23 bits of BOOT_FS segment descriptor base address. */
+        shld    $16,%esi,%edx
+        mov     %dl,BOOT_FS+4+sym_esi(trampoline_gdt)
+
+        /* Initialize 24-31 bits of BOOT_FS segment descriptor base address. */
+        mov     %dh,BOOT_FS+7+sym_esi(trampoline_gdt)
+
+        /*
+         * Initialize %fs and later use it to access Xen data if possible.
+         * According to Intel 64 and IA-32 Architectures Software Developer's
+         * Manual it is safe to do that without reloading GDTR before.
+         */
+        mov     $BOOT_FS,%edx
+        mov     %edx,%fs
+
         /* Save trampoline address for later use. */
         shl     $4, %ecx
-        mov     %ecx,sym_phys(trampoline_phys)
+        mov     %ecx,sym_fs(trampoline_phys)
+
+        /* Save Xen image load base address for later use. */
+        mov     %esi,sym_fs(xen_phys_start)
+        mov     %esi,sym_fs(trampoline_xen_phys_start)
+
+        /* Setup stack. %ss was initialized earlier. */
+        lea     1024+sym_esi(cpu0_stack),%esp
 
         /* Save the Multiboot info struct (after relocation) for later use. */
-        mov     $sym_phys(cpu0_stack)+1024,%esp
         push    %ecx                /* Boot trampoline address. */
         push    %ebx                /* Multiboot information address. */
         push    %eax                /* Multiboot magic. */
         call    reloc
-        mov     %eax,sym_phys(multiboot_ptr)
+        mov     %eax,sym_fs(multiboot_ptr)
 
         /*
          * Do not zero BSS on EFI platform here.
          * It was initialized earlier.
          */
-        cmpb    $0,sym_phys(efi_platform)
+        cmpb    $0,sym_fs(efi_platform)
         jnz     1f
 
         /* Initialize BSS (no nasty surprises!). */
         mov     $sym_phys(__bss_start),%edi
         mov     $sym_phys(__bss_end),%ecx
+        push    %fs
+        pop     %es
         sub     %edi,%ecx
         xor     %eax,%eax
         shr     $2,%ecx
         rep stosl
+        push    %ds
+        pop     %es
 
 1:
         /* Interrogate CPU extended features via CPUID. */
@@ -470,8 +528,8 @@  trampoline_setup:
         jbe     1f
         mov     $0x80000001,%eax
         cpuid
-1:      mov     %edx,sym_phys(cpuid_ext_features)
-        mov     %edx,sym_phys(boot_cpu_data)+CPUINFO_FEATURE_OFFSET(X86_FEATURE_LM)
+1:      mov     %edx,sym_fs(cpuid_ext_features)
+        mov     %edx,sym_fs(boot_cpu_data)+CPUINFO_FEATURE_OFFSET(X86_FEATURE_LM)
 
         /* Check for availability of long mode. */
         bt      $cpufeat_bit(X86_FEATURE_LM),%edx
@@ -479,15 +537,52 @@  trampoline_setup:
 
         /* Stash TSC to calculate a good approximation of time-since-boot */
         rdtsc
-        mov     %eax,sym_phys(boot_tsc_stamp)
-        mov     %edx,sym_phys(boot_tsc_stamp+4)
+        mov     %eax,sym_fs(boot_tsc_stamp)
+        mov     %edx,sym_fs(boot_tsc_stamp)+4
+
+        /*
+         * Update frame addresses in page tables excluding l2_identmap
+         * without its first entry which points to l1_identmap.
+         */
+        mov     $((__page_tables_end-__page_tables_start)/8),%ecx
+        mov     $(((l2_identmap-__page_tables_start)/8)+1),%edx
+1:      cmp     $((l2_identmap+l2_identmap_sizeof-__page_tables_start)/8),%ecx
+        cmove   %edx,%ecx
+        testl   $_PAGE_PRESENT,sym_fs(__page_tables_start)-8(,%ecx,8)
+        jz      2f
+        add     %esi,sym_fs(__page_tables_start)-8(,%ecx,8)
+2:      loop    1b
+
+        /* Initialize L2 boot-map/direct map page table entries (16MB). */
+        lea     sym_esi(start),%ebx
+        lea     (1<<L2_PAGETABLE_SHIFT)*7+(PAGE_HYPERVISOR|_PAGE_PSE)(%ebx),%eax
+        shr     $(L2_PAGETABLE_SHIFT-3),%ebx
+        mov     $8,%ecx
+1:      mov     %eax,sym_fs(l2_bootmap)-8(%ebx,%ecx,8)
+        mov     %eax,sym_fs(l2_identmap)-8(%ebx,%ecx,8)
+        sub     $(1<<L2_PAGETABLE_SHIFT),%eax
+        loop    1b
+
+        /* Initialize L3 boot-map page directory entry. */
+        lea     __PAGE_HYPERVISOR+(L2_PAGETABLE_ENTRIES*8)*3+sym_esi(l2_bootmap),%eax
+        mov     $4,%ecx
+1:      mov     %eax,sym_fs(l3_bootmap)-8(,%ecx,8)
+        sub     $(L2_PAGETABLE_ENTRIES*8),%eax
+        loop    1b
+
+        /*
+         * During boot, hook 4kB mappings of first 2MB of memory into L2.
+         * This avoids mixing cachability for the legacy VGA region.
+         */
+        lea     __PAGE_HYPERVISOR+sym_esi(l1_identmap),%edi
+        mov     %edi,sym_fs(l2_bootmap)
 
         /* Apply relocations to bootstrap trampoline. */
-        mov     sym_phys(trampoline_phys),%edx
+        mov     sym_fs(trampoline_phys),%edx
         mov     $sym_phys(__trampoline_rel_start),%edi
 1:
-        mov     (%edi),%eax
-        add     %edx,(%edi,%eax)
+        mov     %fs:(%edi),%eax
+        add     %edx,%fs:(%edi,%eax)
         add     $4,%edi
         cmp     $sym_phys(__trampoline_rel_stop),%edi
         jb      1b
@@ -496,28 +591,29 @@  trampoline_setup:
         shr     $4,%edx
         mov     $sym_phys(__trampoline_seg_start),%edi
 1:
-        mov     (%edi),%eax
-        mov     %dx,(%edi,%eax)
+        mov     %fs:(%edi),%eax
+        mov     %dx,%fs:(%edi,%eax)
         add     $4,%edi
         cmp     $sym_phys(__trampoline_seg_stop),%edi
         jb      1b
 
         /* Do not parse command line on EFI platform here. */
-        cmpb    $0,sym_phys(efi_platform)
+        cmpb    $0,sym_fs(efi_platform)
         jnz     1f
 
         /* Bail if there is no command line to parse. */
-        mov     sym_phys(multiboot_ptr),%ebx
+        mov     sym_fs(multiboot_ptr),%ebx
         testl   $MBI_CMDLINE,MB_flags(%ebx)
         jz      1f
 
-        pushl   $sym_phys(early_boot_opts)
+        lea     sym_esi(early_boot_opts),%eax
+        push    %eax
         pushl   MB_cmdline(%ebx)
         call    cmdline_parse_early
 
 1:
         /* Switch to low-memory stack.  */
-        mov     sym_phys(trampoline_phys),%edi
+        mov     sym_fs(trampoline_phys),%edi
         lea     0x10000(%edi),%esp
         lea     trampoline_boot_cpu_entry-trampoline_start(%edi),%eax
         pushl   $BOOT_CS32
@@ -526,7 +622,7 @@  trampoline_setup:
         /* Copy bootstrap trampoline to low memory, below 1MB. */
         mov     $sym_phys(trampoline_start),%esi
         mov     $((trampoline_end - trampoline_start) / 4),%ecx
-        rep movsl
+        rep movsl %fs:(%esi),%es:(%edi)
 
         /* Jump into the relocated trampoline. */
         lret
diff --git a/xen/arch/x86/boot/trampoline.S b/xen/arch/x86/boot/trampoline.S
index 2715d17..64f8efd 100644
--- a/xen/arch/x86/boot/trampoline.S
+++ b/xen/arch/x86/boot/trampoline.S
@@ -54,6 +54,11 @@  trampoline_gdt:
         /* 0x0028: real-mode data @ BOOT_TRAMPOLINE */
         .long   0x0000ffff
         .long   0x00009200
+        /*
+         * 0x0030: ring 0 Xen data, 16 MiB size, base
+         * address is computed during runtime.
+         */
+        .quad   0x00c0920000000fff
 
         .pushsection .trampoline_rel, "a"
         .long   trampoline_gdt + BOOT_PSEUDORM_CS + 2 - .
diff --git a/xen/arch/x86/boot/x86_64.S b/xen/arch/x86/boot/x86_64.S
index 7890374..7392004 100644
--- a/xen/arch/x86/boot/x86_64.S
+++ b/xen/arch/x86/boot/x86_64.S
@@ -81,7 +81,6 @@  GLOBAL(boot_cpu_compat_gdt_table)
         .quad 0x0000910000000000     /* per-CPU entry (limit == cpu)      */
         .align PAGE_SIZE, 0
 
-GLOBAL(__page_tables_start)
 /*
  * Mapping of first 2 megabytes of memory. This is mapped with 4kB mappings
  * to avoid type conflicts with fixed-range MTRRs covering the lowest megabyte
@@ -102,6 +101,13 @@  l1_identmap:
         .size l1_identmap, . - l1_identmap
 
 /*
+ * __page_tables_start does not cover l1_identmap because it (l1_identmap)
+ * contains 1-1 mappings. This means that frame addresses of these mappings
+ * are static and should not be updated during runtime.
+ */
+GLOBAL(__page_tables_start)
+
+/*
  * Space for mapping the first 4GB of memory, with the first 16 megabytes
  * actualy mapped (mostly using superpages).  Uses 4x 4k pages.
  */
@@ -186,21 +192,14 @@  GLOBAL(idle_pg_table)
 
 GLOBAL(__page_tables_end)
 
-/* Init pagetables.  Enough page directories to map into the bottom 1GB. */
+/* Init pagetables. Enough page directories to map into 4GB. */
         .section .init.data, "a", @progbits
         .align PAGE_SIZE, 0
 
 GLOBAL(l2_bootmap)
-        .quad sym_phys(l1_identmap) + __PAGE_HYPERVISOR
-        idx = 1
-        .rept 7
-        .quad (idx << L2_PAGETABLE_SHIFT) | __PAGE_HYPERVISOR | _PAGE_PSE
-        idx = idx + 1
-        .endr
-        .fill L2_PAGETABLE_ENTRIES - 8, 8, 0
+        .fill 4 * L2_PAGETABLE_ENTRIES, 8, 0
         .size l2_bootmap, . - l2_bootmap
 
 GLOBAL(l3_bootmap)
-        .quad sym_phys(l2_bootmap) + __PAGE_HYPERVISOR
-        .fill L3_PAGETABLE_ENTRIES - 1, 8, 0
+        .fill L3_PAGETABLE_ENTRIES, 8, 0
         .size l3_bootmap, . - l3_bootmap
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 5d0830e..561a139 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -330,9 +330,6 @@  static void *__init bootstrap_map(const module_t *mod)
     if ( start >= end )
         return NULL;
 
-    if ( end <= BOOTSTRAP_MAP_BASE )
-        return (void *)(unsigned long)start;
-
     ret = (void *)(map_cur + (unsigned long)(start & mask));
     start &= ~mask;
     end = (end + mask) & ~mask;
@@ -716,6 +713,8 @@  void __init noreturn __start_xen(unsigned long mbi_p)
 
     printk("Command line: %s\n", cmdline);
 
+    printk("Xen image load base address: %#lx\n", xen_phys_start);
+
     printk("Video information:\n");
 
     /* Print VGA display mode information. */
@@ -973,7 +972,7 @@  void __init noreturn __start_xen(unsigned long mbi_p)
                     /* Not present, 1GB mapping, or already relocated? */
                     if ( !(l3e_get_flags(*pl3e) & _PAGE_PRESENT) ||
                          (l3e_get_flags(*pl3e) & _PAGE_PSE) ||
-                         (l3e_get_pfn(*pl3e) > 0x1000) )
+                         (l3e_get_pfn(*pl3e) > PFN_DOWN(xen_phys_start)) )
                         continue;
                     *pl3e = l3e_from_intpte(l3e_get_intpte(*pl3e) +
                                             xen_phys_start);
@@ -983,7 +982,7 @@  void __init noreturn __start_xen(unsigned long mbi_p)
                         /* Not present, PSE, or already relocated? */
                         if ( !(l2e_get_flags(*pl2e) & _PAGE_PRESENT) ||
                              (l2e_get_flags(*pl2e) & _PAGE_PSE) ||
-                             (l2e_get_pfn(*pl2e) > 0x1000) )
+                             (l2e_get_pfn(*pl2e) > PFN_DOWN(xen_phys_start)) )
                             continue;
                         *pl2e = l2e_from_intpte(l2e_get_intpte(*pl2e) +
                                                 xen_phys_start);
@@ -1006,7 +1005,8 @@  void __init noreturn __start_xen(unsigned long mbi_p)
             {
                 unsigned int flags;
 
-                if ( !(l2e_get_flags(*pl2e) & _PAGE_PRESENT) )
+                if ( !(l2e_get_flags(*pl2e) & _PAGE_PRESENT) ||
+                     (l2e_get_pfn(*pl2e) > PFN_DOWN(xen_phys_start)) )
                     continue;
 
                 if ( !using_2M_mapping() )
@@ -1060,6 +1060,8 @@  void __init noreturn __start_xen(unsigned long mbi_p)
                 : "memory" );
 
             bootstrap_map(NULL);
+
+            printk("New Xen image base address: %#lx\n", xen_phys_start);
         }
 
         /* Is the region suitable for relocating the multiboot modules? */
diff --git a/xen/arch/x86/x86_64/asm-offsets.c b/xen/arch/x86/x86_64/asm-offsets.c
index 2a22659..5d7a8e5 100644
--- a/xen/arch/x86/x86_64/asm-offsets.c
+++ b/xen/arch/x86/x86_64/asm-offsets.c
@@ -179,5 +179,8 @@  void __dummy__(void)
     OFFSET(MB2_efi64_ih, multiboot2_tag_efi64_ih_t, pointer);
     BLANK();
 
+    DEFINE(l2_identmap_sizeof, sizeof(l2_identmap));
+    BLANK();
+
     OFFSET(DOMAIN_vm_assist, struct domain, vm_assist);
 }
diff --git a/xen/include/asm-x86/page.h b/xen/include/asm-x86/page.h
index af7d3e8..a54fdd1 100644
--- a/xen/include/asm-x86/page.h
+++ b/xen/include/asm-x86/page.h
@@ -288,7 +288,7 @@  extern root_pgentry_t idle_pg_table[ROOT_PAGETABLE_ENTRIES];
 extern l2_pgentry_t  *compat_idle_pg_table_l2;
 extern unsigned int   m2p_compat_vstart;
 extern l2_pgentry_t l2_xenmap[L2_PAGETABLE_ENTRIES],
-    l2_bootmap[L2_PAGETABLE_ENTRIES];
+    l2_bootmap[4*L2_PAGETABLE_ENTRIES];
 extern l3_pgentry_t l3_bootmap[L3_PAGETABLE_ENTRIES];
 extern l2_pgentry_t l2_identmap[4*L2_PAGETABLE_ENTRIES];
 extern l1_pgentry_t l1_fixmap[L1_PAGETABLE_ENTRIES];