[PATCH] x86_64: Unmap NULL during early bootup

We should zap the low mappings, as soon as possible, so that we can catch
kernel bugs more effectively. Previously early boot had NULL mapped
and didn't trap on NULL references.

This patch introduces boot_level4_pgt, which will always have low identity
addresses mapped.  Druing boot, all the processors will use this as their
level4 pgt.  On BP, we will switch to init_level4_pgt as soon as we enter C
code and zap the low mappings as soon as we are done with the usage of
identity low mapped addresses.  On AP's we will zap the low mappings as
soon as we jump to C code.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 23 insertions, 14 deletions

diff --git a/arch/x86_64/kernel/head.S b/arch/x86_64/kernel/head.S
index b92e5f45ed46..15290968e49d 100644
--- a/arch/x86_64/kernel/head.S
+++ b/arch/x86_64/kernel/head.S
@@ -12,6 +12,7 @@
 
 #include <linux/linkage.h>
 #include <linux/threads.h>
+#include <linux/init.h>
 #include <asm/desc.h>
 #include <asm/segment.h>
 #include <asm/page.h>
@@ -70,7 +71,7 @@ startup_32:
         movl    %eax, %cr4
 
         /* Setup early boot stage 4 level pagetables */
-        movl    $(init_level4_pgt - __START_KERNEL_map), %eax
+        movl    $(boot_level4_pgt - __START_KERNEL_map), %eax
         movl    %eax, %cr3
 
         /* Setup EFER (Extended Feature Enable Register) */
@@ -113,7 +114,7 @@ startup_64:
         movq    %rax, %cr4
 
         /* Setup early boot stage 4 level pagetables. */
-        movq    $(init_level4_pgt - __START_KERNEL_map), %rax
+        movq    $(boot_level4_pgt - __START_KERNEL_map), %rax
         movq    %rax, %cr3
 
         /* Check if nx is implemented */
@@ -240,20 +241,10 @@ ljumpvector:
 ENTRY(stext)
 ENTRY(_stext)
 
-        /*
-         * 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)
-         */
 .org 0x1000
 ENTRY(init_level4_pgt)
-        .quad   0x0000000000002007 + __PHYSICAL_START   /* -> level3_ident_pgt */
-        .fill   255,8,0
-        .quad   0x000000000000a007 + __PHYSICAL_START
-        .fill   254,8,0
-        /* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
-        .quad   0x0000000000003007 + __PHYSICAL_START   /* -> level3_kernel_pgt */
+        /* This gets initialized in x86_64_start_kernel */
+        .fill   512,8,0
 
 .org 0x2000
 ENTRY(level3_ident_pgt)
@@ -350,6 +341,24 @@ ENTRY(wakeup_level4_pgt)
         .quad   0x0000000000003007 + __PHYSICAL_START   /* -> level3_kernel_pgt */
 #endif
 
+#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   0x0000000000002007 + __PHYSICAL_START   /* -> level3_ident_pgt */
+        .fill   255,8,0
+        .quad   0x000000000000a007 + __PHYSICAL_START
+        .fill   254,8,0
+        /* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
+        .quad   0x0000000000003007 + __PHYSICAL_START   /* -> level3_kernel_pgt */
+
         .data
 
         .align 16