x86/mce: Add messages for panic errors in AMD's MCE grading

When a machine error is graded as PANIC by the AMD grading logic, the
MCE handler calls mce_panic(). The notification chain does not come
into effect so the AMD EDAC driver does not decode the errors. In these
cases, the messages displayed to the user are more cryptic and miss
information that might be relevant, like the context in which the error
took place.

Add messages to the grading logic for machine errors so that it is clear
what error it was.

  [ bp: Massage commit message. ]
Signed-off-by: Carlos Bilbao <carlos.bilbao@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Yazen Ghannam <yazen.ghannam@amd.com>
Link: https://lore.kernel.org/r/20220405183212.354606-3-carlos.bilbao@amd.com

arch/x86/kernel/cpu/mce/severity.c

@@ -304,6 +304,7 @@ static noinstr int error_context(struct mce *m, struct pt_regs *regs)
 /* See AMD PPR(s) section Machine Check Error Handling. */
 static noinstr int mce_severity_amd(struct mce *m, struct pt_regs *regs, char **msg, bool is_excp)
 {
+	char *panic_msg = NULL;
 	int ret;
 
 	/*
@@ -314,6 +315,7 @@ static noinstr int mce_severity_amd(struct mce *m, struct pt_regs *regs, char **
 
 	/* Processor Context Corrupt, no need to fumble too much, die! */
 	if (m->status & MCI_STATUS_PCC) {
+		panic_msg = "Processor Context Corrupt";
 		ret = MCE_PANIC_SEVERITY;
 		goto out;
 	}
@@ -337,19 +339,26 @@ static noinstr int mce_severity_amd(struct mce *m, struct pt_regs *regs, char **
 	 * system will not be able to recover, panic.
 	 */
 	if ((m->status & MCI_STATUS_OVER) && !mce_flags.overflow_recov) {
+		panic_msg = "Overflowed uncorrected error without MCA Overflow Recovery";
 		ret = MCE_PANIC_SEVERITY;
 		goto out;
 	}
 
 	if (!mce_flags.succor) {
+		panic_msg = "Uncorrected error without MCA Recovery";
 		ret = MCE_PANIC_SEVERITY;
 		goto out;
 	}
 
-	if (error_context(m, regs) == IN_KERNEL)
+	if (error_context(m, regs) == IN_KERNEL) {
+		panic_msg = "Uncorrected unrecoverable error in kernel context";
 		ret = MCE_PANIC_SEVERITY;
+	}
 
 out:
+	if (msg && panic_msg)
+		*msg = panic_msg;
+
 	return ret;
 }