[tip: ras/urgent] x86/mce: Ensure user polling settings are honored when restarting timer

["tip-bot2 for Yazen Ghannam" <tip-bot2@linutronix.de>]

The following commit has been merged into the ras/urgent branch of tip:

Commit-ID:     00c092de6f28ebd32208aef83b02d61af2229b60
Gitweb:        https://git.kernel.org/tip/00c092de6f28ebd32208aef83b02d61af2229b60
Author:        Yazen Ghannam <yazen.ghannam@amd.com>
AuthorDate:    Tue, 24 Jun 2025 14:15:57 
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Fri, 27 Jun 2025 12:41:44 +02:00

x86/mce: Ensure user polling settings are honored when restarting timer

Users can disable MCA polling by setting the "ignore_ce" parameter or by
setting "check_interval=0". This tells the kernel to *not* start the MCE
timer on a CPU.

If the user did not disable CMCI, then storms can occur. When these
happen, the MCE timer will be started with a fixed interval. After the
storm subsides, the timer's next interval is set to check_interval.

This disregards the user's input through "ignore_ce" and
"check_interval". Furthermore, if "check_interval=0", then the new timer
will run faster than expected.

Create a new helper to check these conditions and use it when a CMCI
storm ends.

  [ bp: Massage. ]

Fixes: 7eae17c4add5 ("x86/mce: Add per-bank CMCI storm mitigation")
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/20250624-wip-mca-updates-v4-2-236dd74f645f@amd.com
---
 arch/x86/kernel/cpu/mce/core.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 07d6193..4da4eab 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1740,6 +1740,11 @@ static void mc_poll_banks_default(void)
 
 void (*mc_poll_banks)(void) = mc_poll_banks_default;
 
+static bool should_enable_timer(unsigned long iv)
+{
+	return !mca_cfg.ignore_ce && iv;
+}
+
 static void mce_timer_fn(struct timer_list *t)
 {
 	struct timer_list *cpu_t = this_cpu_ptr(&mce_timer);
@@ -1763,7 +1768,7 @@ static void mce_timer_fn(struct timer_list *t)
 
 	if (mce_get_storm_mode()) {
 		__start_timer(t, HZ);
-	} else {
+	} else if (should_enable_timer(iv)) {
 		__this_cpu_write(mce_next_interval, iv);
 		__start_timer(t, iv);
 	}
@@ -2156,11 +2161,10 @@ static void mce_start_timer(struct timer_list *t)
 {
 	unsigned long iv = check_interval * HZ;
 
-	if (mca_cfg.ignore_ce || !iv)
-		return;
-
-	this_cpu_write(mce_next_interval, iv);
-	__start_timer(t, iv);
+	if (should_enable_timer(iv)) {
+		this_cpu_write(mce_next_interval, iv);
+		__start_timer(t, iv);
+	}
 }
 
 static void __mcheck_cpu_setup_timer(void)