linux-kernel - [PATCH] x86/mce: Don't check for "OVER" bit on action optional machine checks

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Date:   Thu, 18 Jul 2019 11:29:20 -0700
From:   Tony Luck <tony.luck@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Tony Luck <tony.luck@...el.com>,
        Yongkai Wu <yongkaiwu@...cent.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] x86/mce: Don't check for "OVER" bit on action optional machine checks

We currently do not process  SRAO (Software Recoverable Action Optional)
machine checks if they are logged with the overflow bit set to 1 in the
machine check bank status register. This is overly conservative.

There are two cases where we could end up with an SRAO+OVER log based
on the SDM volume 3 overwrite rules in "Table 15-8. Overwrite Rules for
UC, CE, and UCR Errors"

1) First a corrected error is logged, then the SRAO error overwrites.
   The second error overwrites the first because uncorrected errors
   have a higher severity than corrected errors.
2) The SRAO error was logged first, followed by a correcetd error.
   In this case the first error is retained in the bank.

So in either case the machine check bank will contain the address
of the SRAO error. So we can process that even if the overflow bit
was set.

Reported-by: Yongkai Wu <yongkaiwu@...cent.com>
Signed-off-by: Tony Luck <tony.luck@...el.com>
---
 arch/x86/kernel/cpu/mce/severity.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c
index 210f1f5db5f7..87bcdc6dc2f0 100644
--- a/arch/x86/kernel/cpu/mce/severity.c
+++ b/arch/x86/kernel/cpu/mce/severity.c
@@ -107,11 +107,11 @@ static struct severity {
 	 */
 	MCESEV(
 		AO, "Action optional: memory scrubbing error",
-		SER, MASK(MCI_STATUS_OVER|MCI_UC_AR|MCACOD_SCRUBMSK, MCI_STATUS_UC|MCACOD_SCRUB)
+		SER, MASK(MCI_UC_AR|MCACOD_SCRUBMSK, MCI_STATUS_UC|MCACOD_SCRUB)
 		),
 	MCESEV(
 		AO, "Action optional: last level cache writeback error",
-		SER, MASK(MCI_STATUS_OVER|MCI_UC_AR|MCACOD, MCI_STATUS_UC|MCACOD_L3WB)
+		SER, MASK(MCI_UC_AR|MCACOD, MCI_STATUS_UC|MCACOD_L3WB)
 		),

 	/* ignore OVER for UCNA */
-- 
2.20.1