linux-kernel - [PATCH 1/8] x86/mce: Stop mce_reign() from re-computing severity for every CPU

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Date:   Tue,  8 Sep 2020 10:55:12 -0700
From:   Tony Luck <tony.luck@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Tony Luck <tony.luck@...el.com>,
        Youquan Song <youquan.song@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/8] x86/mce: Stop mce_reign() from re-computing severity for every CPU

Back in:

commit 20d51a426fe9 ("x86/mce: Reuse one of the u16 padding fields in 'struct mce'")

a field was added to "struct mce" to save the computed error severity.

Make use of this in mce_reign() to avoid re-computing the severity
for every CPU.

In the case where we panic, we do still need one call to mce_severity to
provide the correct message giving the reason for the panic.

Signed-off-by: Tony Luck <tony.luck@...el.com>
---
 arch/x86/kernel/cpu/mce/core.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index f43a78bde670..fb6b5f64f7e6 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -872,7 +872,6 @@ static void mce_reign(void)
 	struct mce *m = NULL;
 	int global_worst = 0;
 	char *msg = NULL;
-	char *nmsg = NULL;
 
 	/*
 	 * This CPU is the Monarch and the other CPUs have run
@@ -880,12 +879,10 @@ static void mce_reign(void)
 	 * Grade the severity of the errors of all the CPUs.
 	 */
 	for_each_possible_cpu(cpu) {
-		int severity = mce_severity(&per_cpu(mces_seen, cpu),
-					    mca_cfg.tolerant,
-					    &nmsg, true);
-		if (severity > global_worst) {
-			msg = nmsg;
-			global_worst = severity;
+		struct mce *mtmp = &per_cpu(mces_seen, cpu);
+
+		if (mtmp->severity > global_worst) {
+			global_worst = mtmp->severity;
 			m = &per_cpu(mces_seen, cpu);
 		}
 	}
@@ -895,8 +892,11 @@ static void mce_reign(void)
 	 * This dumps all the mces in the log buffer and stops the
 	 * other CPUs.
 	 */
-	if (m && global_worst >= MCE_PANIC_SEVERITY && mca_cfg.tolerant < 3)
+	if (m && global_worst >= MCE_PANIC_SEVERITY && mca_cfg.tolerant < 3) {
+		/* call mce_severity() to get "msg" for panic */
+		mce_severity(m, mca_cfg.tolerant, &msg, true);
 		mce_panic("Fatal machine check", m, msg);
+	}
 
 	/*
 	 * For UC somewhere we let the CPU who detects it handle it.
-- 
2.21.1