linux-kernel - RE: [PATCH v2 2/2] x86/mce: Add messages to describe panic machine errors on AMD's MCEs grading

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Date:   Thu, 31 Mar 2022 17:17:45 +0000
From:   "Day, Michael" <Michael.Day@....com>
To:     "Bilbao, Carlos" <Carlos.Bilbao@....com>,
        "bp@...en8.de" <bp@...en8.de>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "Ghannam, Yazen" <Yazen.Ghannam@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "bilbao@...edu" <bilbao@...edu>
Subject: RE: [PATCH v2 2/2] x86/mce: Add messages to describe panic machine
 errors on AMD's MCEs grading

[AMD Official Use Only]

-----Original Message-----
From: Bilbao, Carlos <Carlos.Bilbao@....com> 
Sent: Thursday, March 31, 2022 12:39 PM
To: bp@...en8.de
Cc: tglx@...utronix.de; mingo@...hat.com; dave.hansen@...ux.intel.com; x86@...nel.org; Ghannam, Yazen <Yazen.Ghannam@....com>; linux-kernel@...r.kernel.org; linux-edac@...r.kernel.org; bilbao@...edu; Bilbao, Carlos <Carlos.Bilbao@....com>
Subject: [PATCH v2 2/2] x86/mce: Add messages to describe panic machine errors on AMD's MCEs grading

When a machine error is graded as PANIC by 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.

Fix the above issue including messages on AMD's grading logic for machine errors graded as PANIC.

Signed-off-by: Carlos Bilbao <carlos.bilbao@....com>
---
 arch/x86/kernel/cpu/mce/severity.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c
index 4d52eef21230..ea4b9407bbad 100644
--- a/arch/x86/kernel/cpu/mce/severity.c
+++ b/arch/x86/kernel/cpu/mce/severity.c
@@ -307,6 +307,7 @@ static noinstr int error_context(struct mce *m, struct pt_regs *regs)  static noinstr int mce_severity_amd(struct mce *m, struct pt_regs *regs, char **msg, bool is_excp)  {
 	int ret;
+	char *panic_msg;

I suggest char *panic_msg = NULL;

Simply because its stack-based and a non-null value may get assigned to *msg after the amd_severity: label. 
 
 	/*
 	 * Default return value: Action required, the error must be handled @@ -316,6 +317,7 @@ 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 amd_severity;
 	}
@@ -339,16 +341,21 @@ static noinstr int mce_severity_amd(struct mce *m, struct pt_regs *regs, char **
 
 	if (((m->status & MCI_STATUS_OVER) && !mce_flags.overflow_recov)
 	     || !mce_flags.succor) {
+		panic_msg = "Uncorrected unrecoverable error";
 		ret = MCE_PANIC_SEVERITY;
 		goto amd_severity;
 	}
 
 	if (error_context(m, regs) == IN_KERNEL) {
+		panic_msg = "Uncorrected error in kernel context";
 		ret = MCE_PANIC_SEVERITY;
 	}
 
 amd_severity:
 
+	if (msg && panic_msg)
+		*msg = panic_msg;
+
 	return ret;
 }
 
--
2.31.1