[RFC Patch 1/2][slimdump] Append CRASH_REASON to VMCOREINFO elf-note

["K.Prasad" <prasad@linux.vnet.ibm.com>]

Allow various crash paths to append the reason of crash into the
VMCOREINFO elf-note through the field CRASH_REASON. We also make the
fatal machine check exceptions append "PANIC_MCE" as the crash reason.
This string will be recognised by upstream tools like makedumpfile and
crash to generate slimdump.

With increased usage of the CRASH_REASON field, the crash strings can be
encoded for better usage.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 arch/x86/kernel/cpu/mcheck/mce.c |    8 ++++++++
 kernel/kexec.c                   |    6 ++++++
 2 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 362056a..5b2cb6a 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -38,6 +38,7 @@
 #include <linux/debugfs.h>
 #include <linux/irq_work.h>
 #include <linux/export.h>
+#include <linux/kexec.h>
 
 #include <asm/processor.h>
 #include <asm/mce.h>
@@ -240,6 +241,13 @@ static atomic_t mce_paniced;
 static int fake_panic;
 static atomic_t mce_fake_paniced;
 
+char *arch_add_crash_reason(void)
+{
+	static char crash_reason[] = "PANIC_MCE";
+
+	return crash_reason;
+}
+
 /* Panic in progress. Enable interrupts and wait for final IPI */
 static void wait_for_panic(void)
 {
diff --git a/kernel/kexec.c b/kernel/kexec.c
index dc7bc08..a731693 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -1080,6 +1080,11 @@ asmlinkage long compat_sys_kexec_load(unsigned long entry,
 }
 #endif
 
+__weak char *arch_add_crash_reason(void)
+{
+	return (char *)NULL;
+}
+
 void crash_kexec(struct pt_regs *regs)
 {
 	/* Take the kexec_mutex here to prevent sys_kexec_load
@@ -1411,6 +1416,7 @@ static void update_vmcoreinfo_note(void)
 void crash_save_vmcoreinfo(void)
 {
 	vmcoreinfo_append_str("CRASHTIME=%ld", get_seconds());
+	vmcoreinfo_append_str("\nCRASH_REASON=%s\n", arch_add_crash_reason());
 	update_vmcoreinfo_note();
 }