[PATCH] x86-64: Remove the identity mapping as early as possible

With the rewrite of the SMP trampoline and the early page
allocator there is nothing that needs identity mapped pages,
once we start executing C code.

So add zap_identity_mappings into head64.c and remove
zap_low_mappings() from much later in the code.  The functions
 are subtly different thus the name change.

This also kills boot_level4_pgt which was from an earlier
attempt to move the identity mappings as early as possible,
and is now no longer needed.  Essentially I have replaced
boot_level4_pgt with trampoline_level4_pgt in trampoline.S

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 14 insertions, 25 deletions

diff --git a/arch/x86_64/kernel/head.S b/arch/x86_64/kernel/head.S
index 926aa2197aaa..c211e52f1333 100644
--- a/arch/x86_64/kernel/head.S
+++ b/arch/x86_64/kernel/head.S
@@ -71,7 +71,7 @@ startup_32:
         movl    %eax, %cr4
 
         /* Setup early boot stage 4 level pagetables */
-        movl    $(boot_level4_pgt - __START_KERNEL_map), %eax
+        movl    $(init_level4_pgt - __START_KERNEL_map), %eax
         movl    %eax, %cr3
 
         /* Setup EFER (Extended Feature Enable Register) */
@@ -115,7 +115,7 @@ ENTRY(secondary_startup_64)
         movq    %rax, %cr4
 
         /* Setup early boot stage 4 level pagetables. */
-        movq    $(boot_level4_pgt - __START_KERNEL_map), %rax
+        movq    $(init_level4_pgt - __START_KERNEL_map), %rax
         movq    %rax, %cr3
 
         /* Check if nx is implemented */
@@ -274,9 +274,19 @@ ENTRY(name)
         i = i + 1 ;                             \
         .endr
 
+        /*
+         * This default setting generates an ident mapping at address 0x100000
+         * and a mapping for the kernel that precisely maps virtual address
+         * 0xffffffff80000000 to physical address 0x000000. (always using
+         * 2Mbyte large pages provided by PAE mode)
+         */
 NEXT_PAGE(init_level4_pgt)
-        /* This gets initialized in x86_64_start_kernel */
-        .fill   512,8,0
+        .quad   level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
+        .fill   257,8,0
+        .quad   level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
+        .fill   252,8,0
+        /* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
+        .quad   level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE
 
 NEXT_PAGE(level3_ident_pgt)
         .quad   level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
@@ -307,27 +317,6 @@ NEXT_PAGE(level2_kernel_pgt)
 #undef NEXT_PAGE
 
         .data
-
-#ifndef CONFIG_HOTPLUG_CPU
-        __INITDATA
-#endif
-        /*
-         * This default setting generates an ident mapping at address 0x100000
-         * and a mapping for the kernel that precisely maps virtual address
-         * 0xffffffff80000000 to physical address 0x000000. (always using
-         * 2Mbyte large pages provided by PAE mode)
-         */
-        .align PAGE_SIZE
-ENTRY(boot_level4_pgt)
-        .quad   level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
-        .fill   257,8,0
-        .quad   level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
-        .fill   252,8,0
-        /* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
-        .quad   level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE
-
-        .data
-
         .align 16
         .globl cpu_gdt_descr
 cpu_gdt_descr: