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Subject[PATCH] x86/MCE/AMD: Always give panic severity for UC errors in kernel context
Date
From: Yazen Ghannam <yazen.ghannam@amd.com>

[Upstream commit d65dfc81bb3894fdb68cbc74bbf5fb48d2354071]

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: <stable@vger.kernel.org> # 4.1.x, 4.4.x
Fixes: bf80bbd7dcf5 (x86/mce: Add an AMD severities-grading function)
---
Same as
d65dfc81bb38 ("x86/MCE/AMD: Always give panic severity for UC errors in kernel context")
but fixed up to apply to v4.1 and v4.4 stable branches.

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 9c682c222071..a9287f0f06f2 100644
--- a/arch/x86/kernel/cpu/mcheck/mce-severity.c
+++ b/arch/x86/kernel/cpu/mcheck/mce-severity.c
@@ -200,6 +200,9 @@ 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
@@ -207,10 +210,6 @@ static int mce_severity_amd(struct mce *m, int tolerant, char **msg, bool is_exc
* to at least kill process to prolong system operation.
*/
if (mce_flags.overflow_recov) {
- /* 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 {
--
2.14.1
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