linux-kernel - [tip:ras/core] x86/MCE/AMD: Always give panic severity for UC errors in kernel context

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Date:   Tue, 7 Nov 2017 02:15:46 -0800
From:   tip-bot for Yazen Ghannam <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     tony.luck@...el.com, bp@...e.de, yazen.ghannam@....com,
        peterz@...radead.org, linux-kernel@...r.kernel.org, hpa@...or.com,
        torvalds@...ux-foundation.org, linux-edac@...r.kernel.org,
        tglx@...utronix.de, mingo@...nel.org
Subject: [tip:ras/core] x86/MCE/AMD: Always give panic severity for UC
 errors in kernel context

Commit-ID:  d65dfc81bb3894fdb68cbc74bbf5fb48d2354071
Gitweb:     https://git.kernel.org/tip/d65dfc81bb3894fdb68cbc74bbf5fb48d2354071
Author:     Yazen Ghannam <yazen.ghannam@....com>
AuthorDate: Mon, 6 Nov 2017 18:46:32 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 7 Nov 2017 11:07:50 +0100

x86/MCE/AMD: Always give panic severity for UC errors in kernel context

The AMD severity grading function was introduced in kernel 4.1. The
current logic can possibly give MCE_AR_SEVERITY for uncorrectable
errors in kernel context. The system may then get stuck in a loop as
memory_failure() will try to handle the bad kernel memory and find it
busy.

Return MCE_PANIC_SEVERITY for all UC errors IN_KERNEL context on AMD
systems.

After:

  b2f9d678e28c ("x86/mce: Check for faults tagged in EXTABLE_CLASS_FAULT exception table entries")

was accepted in v4.6, this issue was masked because of the tail-end attempt
at kernel mode recovery in the #MC handler.

However, uncorrectable errors IN_KERNEL context should always be considered
unrecoverable and cause a panic.

Signed-off-by: Yazen Ghannam <yazen.ghannam@....com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: <stable@...r.kernel.org> # 4.9.x
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Tony Luck <tony.luck@...el.com>
Cc: linux-edac <linux-edac@...r.kernel.org>
Fixes: bf80bbd7dcf5 (x86/mce: Add an AMD severities-grading function)
Link: http://lkml.kernel.org/r/20171106174633.13576-1-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/cpu/mcheck/mce-severity.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce-severity.c b/arch/x86/kernel/cpu/mcheck/mce-severity.c
index 87cc9ab..4b81876 100644
--- a/arch/x86/kernel/cpu/mcheck/mce-severity.c
+++ b/arch/x86/kernel/cpu/mcheck/mce-severity.c
@@ -245,6 +245,9 @@ static int mce_severity_amd(struct mce *m, int tolerant, char **msg, bool is_exc
 
 	if (m->status & MCI_STATUS_UC) {
 
+		if (ctx == IN_KERNEL)
+			return MCE_PANIC_SEVERITY;
+
 		/*
 		 * On older systems where overflow_recov flag is not present, we
 		 * should simply panic if an error overflow occurs. If
@@ -255,10 +258,6 @@ static int mce_severity_amd(struct mce *m, int tolerant, char **msg, bool is_exc
 			if (mce_flags.smca)
 				return mce_severity_amd_smca(m, ctx);
 
-			/* software can try to contain */
-			if (!(m->mcgstatus & MCG_STATUS_RIPV) && (ctx == IN_KERNEL))
-				return MCE_PANIC_SEVERITY;
-
 			/* kill current process */
 			return MCE_AR_SEVERITY;
 		} else {