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

JIRA: https://issues.redhat.com/browse/RHEL-118444

commit 00c092d
Author: Yazen Ghannam <yazen.ghannam@amd.com>
Date:   Tue Jun 24 14:15:57 2025 +0000

    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: 7eae17c ("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

Signed-off-by: David Arcari <darcari@redhat.com>

Author: darcari

arch/x86/kernel/cpu/mce/core.c

@@ -1739,6 +1739,11 @@ 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);
@@ -1762,7 +1767,7 @@ 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);
 	}
@@ -2155,11 +2160,10 @@ 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)