[PATCH 1/2] x86/MCE/AMD: Always give panic severity for UC errors in kernel context

* [PATCH 1/2] x86/MCE/AMD: Always give panic severity for UC errors in kernel context
@ 2017-11-06 17:46 Borislav Petkov
  2017-11-06 17:46 ` [PATCH 2/2] x86/MCE/AMD: Fix mce_severity_amd_smca() signature Borislav Petkov
  2017-11-07 10:15 ` [tip:ras/core] x86/MCE/AMD: Always give panic severity for UC errors in kernel context tip-bot for Yazen Ghannam
  0 siblings, 2 replies; 4+ messages in thread
From: Borislav Petkov @ 2017-11-06 17:46 UTC (permalink / raw)
  To: X86 ML; +Cc: LKML

From: Yazen Ghannam <yazen.ghannam@amd.com>

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@amd.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Cc: x86-ml <x86@kernel.org>
Link: http://lkml.kernel.org/r/1509562746-6313-1-git-send-email-Yazen.Ghannam@amd.com
Fixes: bf80bbd7dcf5 (x86/mce: Add an AMD severities-grading function)
Cc: <stable@vger.kernel.org> # 4.9.x
Signed-off-by: Borislav Petkov <bp@suse.de>
---
 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 87cc9ab7a13c..4b8187639c2d 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 {
-- 
2.13.0

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