x86: construct the {l2,l3}_bootmap at compile time

... rather than at runtime.

The bootmaps are discarded in zap_low_mappings(), so the tables themselves can
live in .init.data and be reclaimed after boot.

Hooking the l1_identmap into l2_xenmap stays for safety, along with a longer
comment explaining why.

This does not change the EFI construction of {l2,l3}_bootmap.  EFI already
constructs them cleanly in their relocated form.

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

xen/arch/x86/boot/head.S

@@ -150,21 +150,13 @@ __start:
         mov     %eax,sym_phys(boot_tsc_stamp)
         mov     %edx,sym_phys(boot_tsc_stamp+4)
 
-        /* Initialise L2 boot-map page table entries (16MB). */
-        mov     $sym_phys(l2_bootmap),%edx
-        mov     $PAGE_HYPERVISOR|_PAGE_PSE,%eax
-        mov     $8,%ecx
-1:      mov     %eax,(%edx)
-        add     $8,%edx
-        add     $(1<<L2_PAGETABLE_SHIFT),%eax
-        loop    1b
-        /* Initialise L3 boot-map page directory entry. */
-        mov     $sym_phys(l2_bootmap)+__PAGE_HYPERVISOR,%eax
-        mov     %eax,sym_phys(l3_bootmap) + 0*8
-        /* Hook 4kB mappings of first 2MB of memory into L2. */
+        /*
+         * During boot, hook 4kB mappings of first 2MB of memory into L2.
+         * This avoids mixing cachability for the legacy VGA region, and is
+         * corrected when Xen relocates itself.
+         */
         mov     $sym_phys(l1_identmap)+__PAGE_HYPERVISOR,%edi
         mov     %edi,sym_phys(l2_xenmap)
-        mov     %edi,sym_phys(l2_bootmap)
 
         /* Apply relocations to bootstrap trampoline. */
         mov     sym_phys(trampoline_phys),%edx

xen/arch/x86/boot/x86_64.S

@@ -184,3 +184,22 @@ GLOBAL(idle_pg_table)
         .size idle_pg_table, . - idle_pg_table
 
 GLOBAL(__page_tables_end)
+
+/* Init pagetables.  Enough page directories to map into the bottom 1GB. */
+        .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
+        .size l2_bootmap, . - l2_bootmap
+
+GLOBAL(l3_bootmap)
+        .quad sym_phys(l2_bootmap) + __PAGE_HYPERVISOR
+        .fill L3_PAGETABLE_ENTRIES - 1, 8, 0
+        .size l3_bootmap, . - l3_bootmap

xen/arch/x86/x86_64/mm.c

@@ -42,10 +42,6 @@ asm(".file \"" __FILE__ "\"");
 
 unsigned int __read_mostly m2p_compat_vstart = __HYPERVISOR_COMPAT_VIRT_START;
 
-/* Enough page directories to map into the bottom 1GB. */
-l3_pgentry_t __section(".bss.page_aligned") l3_bootmap[L3_PAGETABLE_ENTRIES];
-l2_pgentry_t __section(".bss.page_aligned") l2_bootmap[L2_PAGETABLE_ENTRIES];
-
 l2_pgentry_t *compat_idle_pg_table_l2;
 
 void *do_page_walk(struct vcpu *v, unsigned long addr)