x86, kexec: Limit the crashkernel address appropriately

Keep the crash kernel address below 512 MiB for 32 bits and 896 MiB
for 64 bits.  For 32 bits, this retains compatibility with earlier
kernel releases, and makes it work even if the vmalloc= setting is
adjusted.

For 64 bits, we should be able to increase this substantially once a
hard-coded limit in kexec-tools is fixed.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <20101217195035.GE14502@redhat.com>

arch/x86/kernel/setup.c

@@ -501,7 +501,18 @@ static inline unsigned long long get_total_mem(void)
 	return total << PAGE_SHIFT;
 }
 
-#define DEFAULT_BZIMAGE_ADDR_MAX 0x37FFFFFF
+/*
+ * Keep the crash kernel below this limit.  On 32 bits earlier kernels
+ * would limit the kernel to the low 512 MiB due to mapping restrictions.
+ * On 64 bits, kexec-tools currently limits us to 896 MiB; increase this
+ * limit once kexec-tools are fixed.
+ */
+#ifdef CONFIG_X86_32
+# define CRASH_KERNEL_ADDR_MAX	(512 << 20)
+#else
+# define CRASH_KERNEL_ADDR_MAX	(896 << 20)
+#endif
+
 static void __init reserve_crashkernel(void)
 {
 	unsigned long long total_mem;
@@ -520,10 +531,10 @@ static void __init reserve_crashkernel(void)
 		const unsigned long long alignment = 16<<20;	/* 16M */
 
 		/*
-		 *  kexec want bzImage is below DEFAULT_BZIMAGE_ADDR_MAX
+		 *  kexec want bzImage is below CRASH_KERNEL_ADDR_MAX
 		 */
 		crash_base = memblock_find_in_range(alignment,
-			       DEFAULT_BZIMAGE_ADDR_MAX, crash_size, alignment);
+			       CRASH_KERNEL_ADDR_MAX, crash_size, alignment);
 
 		if (crash_base == MEMBLOCK_ERROR) {
 			pr_info("crashkernel reservation failed - No suitable area found.\n");