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

[Yazen Ghannam <Yazen.Ghannam@amd.com>]

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

Our current AMD severity logic can possibly give MCE_AR_SEVERITY for
uncorrectable errors in kernel context. The current #MC handler only calls
memory_failure() on errors in user context, but older versions will call
memory_failure() unconditionally. In older versions, the system can 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. Newer
kernel versions have IN_KERNEL_RECOV context for recoverable kernel errors.
All others kernel uncorrectable errors can be considered unrecoverable.

Fixes: bf80bbd7dcf5 (x86/mce: Add an AMD severities-grading function)

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Cc: <stable@vger.kernel.org> # v4.9..
---
 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 2773c8547f69..f5518706baa6 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 {
-- 
2.7.4