[PATCH] kexec: x86_64: add CONFIG_PHYSICAL_START

For one kernel to report a crash another kernel has created we need
to have 2 kernels loaded simultaneously in memory.  To accomplish this
the two kernels need to built to run at different physical addresses.

This patch adds the CONFIG_PHYSICAL_START option to the x86_64 kernel
so we can do just that.  You need to know what you are doing and
the ramifications are before changing this value, and most users
won't care so I have made it depend on CONFIG_EMBEDDED

bzImage kernels will work and run at a different address when compiled
with this option but they will still load at 1MB.  If you need a kernel
loaded at a different address as well you need to boot a vmlinux.

Signed-off-by: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

5 files changed, 32 insertions, 17 deletions

diff --git a/arch/x86_64/Kconfig b/arch/x86_64/Kconfig
index a853d87ff7e3..56c02cf6397d 100644
--- a/arch/x86_64/Kconfig
+++ b/arch/x86_64/Kconfig
@@ -369,6 +369,17 @@ config X86_MCE_INTEL
            Additional support for intel specific MCE features such as
            the thermal monitor.
 
+config PHYSICAL_START
+        hex "Physical address where the kernel is loaded" if EMBEDDED
+        default "0x100000"
+        help
+          This gives the physical address where the kernel is loaded.
+          Primarily used in the case of kexec on panic where the
+          fail safe kernel needs to run at a different address than
+          the panic-ed kernel.
+
+          Don't change this unless you know what you are doing.
+
 config SECCOMP
         bool "Enable seccomp to safely compute untrusted bytecode"
         depends on PROC_FS
diff --git a/arch/x86_64/boot/compressed/head.S b/arch/x86_64/boot/compressed/head.S
index 27264dbd575c..b0df2aeff5dc 100644
--- a/arch/x86_64/boot/compressed/head.S
+++ b/arch/x86_64/boot/compressed/head.S
@@ -28,6 +28,7 @@
 
 #include <linux/linkage.h>
 #include <asm/segment.h>
+#include <asm/page.h>
 
         .code32
         .globl startup_32
@@ -77,7 +78,7 @@ startup_32:
         jnz  3f
         addl $8,%esp
         xorl %ebx,%ebx
-        ljmp $(__KERNEL_CS), $0x100000
+        ljmp $(__KERNEL_CS), $__PHYSICAL_START
 
 /*
  * We come here, if we were loaded high.
@@ -103,7 +104,7 @@ startup_32:
         popl %ecx       # lcount
         popl %edx       # high_buffer_start
         popl %eax       # hcount
-        movl $0x100000,%edi
+        movl $__PHYSICAL_START,%edi
         cli             # make sure we don't get interrupted
         ljmp $(__KERNEL_CS), $0x1000 # and jump to the move routine
 
@@ -128,7 +129,7 @@ move_routine_start:
         movsl
         movl %ebx,%esi  # Restore setup pointer
         xorl %ebx,%ebx
-        ljmp $(__KERNEL_CS), $0x100000
+        ljmp $(__KERNEL_CS), $__PHYSICAL_START
 move_routine_end:
 
 
diff --git a/arch/x86_64/boot/compressed/misc.c b/arch/x86_64/boot/compressed/misc.c
index c8b9216f9e63..c43cedb5c1d7 100644
--- a/arch/x86_64/boot/compressed/misc.c
+++ b/arch/x86_64/boot/compressed/misc.c
@@ -11,6 +11,7 @@
 
 #include "miscsetup.h"
 #include <asm/io.h>
+#include <asm/page.h>
 
 /*
  * gzip declarations
@@ -284,7 +285,7 @@ void setup_normal_output_buffer(void)
 #else
         if ((ALT_MEM_K > EXT_MEM_K ? ALT_MEM_K : EXT_MEM_K) < 1024) error("Less than 2MB of memory");
 #endif
-        output_data = (char *)0x100000; /* Points to 1M */
+        output_data = (char *)__PHYSICAL_START; /* Normally Points to 1M */
         free_mem_end_ptr = (long)real_mode;
 }
 
@@ -307,8 +308,8 @@ void setup_output_buffer_if_we_run_high(struct moveparams *mv)
         low_buffer_size = low_buffer_end - LOW_BUFFER_START;
         high_loaded = 1;
         free_mem_end_ptr = (long)high_buffer_start;
-        if ( (0x100000 + low_buffer_size) > ((ulg)high_buffer_start)) {
-                high_buffer_start = (uch *)(0x100000 + low_buffer_size);
+        if ( (__PHYSICAL_START + low_buffer_size) > ((ulg)high_buffer_start)) {
+                high_buffer_start = (uch *)(__PHYSICAL_START + low_buffer_size);
                 mv->hcount = 0; /* say: we need not to move high_buffer */
         }
         else mv->hcount = -1;
diff --git a/arch/x86_64/kernel/head.S b/arch/x86_64/kernel/head.S
index 9bd2e7a4b81e..8d765aa77a26 100644
--- a/arch/x86_64/kernel/head.S
+++ b/arch/x86_64/kernel/head.S
@@ -248,23 +248,23 @@ ENTRY(_stext)
          */
 .org 0x1000
 ENTRY(init_level4_pgt)
-        .quad   0x0000000000102007              /* -> level3_ident_pgt */
+        .quad   0x0000000000002007 + __PHYSICAL_START   /* -> level3_ident_pgt */
         .fill   255,8,0
-        .quad   0x000000000010a007
+        .quad   0x000000000000a007 + __PHYSICAL_START
         .fill   254,8,0
         /* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
-        .quad   0x0000000000103007              /* -> level3_kernel_pgt */
+        .quad   0x0000000000003007 + __PHYSICAL_START   /* -> level3_kernel_pgt */
 
 .org 0x2000
 ENTRY(level3_ident_pgt)
-        .quad   0x0000000000104007
+        .quad   0x0000000000004007 + __PHYSICAL_START
         .fill   511,8,0
 
 .org 0x3000
 ENTRY(level3_kernel_pgt)
         .fill   510,8,0
         /* (2^48-(2*1024*1024*1024)-((2^39)*511))/(2^30) = 510 */
-        .quad   0x0000000000105007              /* -> level2_kernel_pgt */
+        .quad   0x0000000000005007 + __PHYSICAL_START   /* -> level2_kernel_pgt */
         .fill   1,8,0
 
 .org 0x4000
@@ -337,17 +337,17 @@ ENTRY(empty_bad_pmd_table)
 
 .org 0xa000
 ENTRY(level3_physmem_pgt)
-        .quad   0x0000000000105007              /* -> level2_kernel_pgt (so that __va works even before pagetable_init) */
+        .quad   0x0000000000005007 + __PHYSICAL_START   /* -> level2_kernel_pgt (so that __va works even before pagetable_init) */
 
         .org 0xb000
 #ifdef CONFIG_ACPI_SLEEP
 ENTRY(wakeup_level4_pgt)
-        .quad   0x0000000000102007              /* -> level3_ident_pgt */
+        .quad   0x0000000000002007 + __PHYSICAL_START   /* -> level3_ident_pgt */
         .fill   255,8,0
-        .quad   0x000000000010a007
+        .quad   0x000000000000a007 + __PHYSICAL_START
         .fill   254,8,0
         /* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
-        .quad   0x0000000000103007              /* -> level3_kernel_pgt */
+        .quad   0x0000000000003007 + __PHYSICAL_START   /* -> level3_kernel_pgt */
 #endif
 
         .data
diff --git a/include/asm-x86_64/page.h b/include/asm-x86_64/page.h
index 60130f4ca986..431318764af6 100644
--- a/include/asm-x86_64/page.h
+++ b/include/asm-x86_64/page.h
@@ -64,12 +64,14 @@ typedef struct { unsigned long pgprot; } pgprot_t;
 #define __pgd(x) ((pgd_t) { (x) } )
 #define __pgprot(x)     ((pgprot_t) { (x) } )
 
-#define __START_KERNEL          0xffffffff80100000UL
+#define __PHYSICAL_START        ((unsigned long)CONFIG_PHYSICAL_START)
+#define __START_KERNEL          (__START_KERNEL_map + __PHYSICAL_START)
 #define __START_KERNEL_map      0xffffffff80000000UL
 #define __PAGE_OFFSET           0xffff810000000000UL
 
 #else
-#define __START_KERNEL          0xffffffff80100000
+#define __PHYSICAL_START        CONFIG_PHYSICAL_START
+#define __START_KERNEL          (__START_KERNEL_map + __PHYSICAL_START)
 #define __START_KERNEL_map      0xffffffff80000000
 #define __PAGE_OFFSET           0xffff810000000000
 #endif /* !__ASSEMBLY__ */