Re: [PATCH] mce: prevent concurrent polling of MCE events

[Aristeu Rozanski <aris@ruivo.org>]

Hi Borislav,

On Tue, Jun 06, 2023 at 04:08:48PM +0200, Borislav Petkov wrote:
> Independent of that, yes, we will try not to pollute it with duplicates
> once we know what the issue exactly is which makes people disable CMCI.

how about this (untested, with possibly a short comment on
intel_cmci_poll_lock()):

--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1618,7 +1618,9 @@ static void mce_timer_fn(struct timer_list *t)
 	iv = __this_cpu_read(mce_next_interval);
 
 	if (mce_available(this_cpu_ptr(&cpu_info))) {
+		bool locked = intel_cmci_poll_lock();
 		machine_check_poll(0, this_cpu_ptr(&mce_poll_banks));
+		intel_cmci_poll_unlock(locked);
 
 		if (mce_intel_cmci_poll()) {
 			iv = mce_adjust_timer(iv);
diff --git a/arch/x86/kernel/cpu/mce/intel.c b/arch/x86/kernel/cpu/mce/intel.c
index 95275a5e57e0..c688c088f5cf 100644
--- a/arch/x86/kernel/cpu/mce/intel.c
+++ b/arch/x86/kernel/cpu/mce/intel.c
@@ -73,13 +73,10 @@ enum {
 
 static atomic_t cmci_storm_on_cpus;
 
-static int cmci_supported(int *banks)
+static int cmci_supported_hw(int *banks)
 {
 	u64 cap;
 
-	if (mca_cfg.cmci_disabled || mca_cfg.ignore_ce)
-		return 0;
-
 	/*
 	 * Vendor check is not strictly needed, but the initial
 	 * initialization is vendor keyed and this
@@ -96,6 +93,14 @@ static int cmci_supported(int *banks)
 	return !!(cap & MCG_CMCI_P);
 }
 
+static int cmci_supported(int *banks)
+{
+	if (mca_cfg.cmci_disabled || mca_cfg.ignore_ce)
+		return 0;
+
+	return cmci_supported_hw(banks);
+}
+
 static bool lmce_supported(void)
 {
 	u64 tmp;
@@ -519,3 +524,25 @@ bool intel_filter_mce(struct mce *m)
 
 	return false;
 }
+
+static DEFINE_SPINLOCK(cmci_poll_lock);
+bool intel_cmci_poll_lock(void)
+{
+	int banks;
+
+	if (!cmci_supported_hw(&banks))
+		return false;
+
+	spin_lock(&cmci_poll_lock);
+
+	return true;
+}
+
+void intel_cmci_poll_unlock(bool locked)
+{
+	if (!locked)
+		return;
+
+	spin_unlock(&cmci_poll_lock);
+}
+
diff --git a/arch/x86/kernel/cpu/mce/internal.h b/arch/x86/kernel/cpu/mce/internal.h
index d2412ce2d312..25bcc4a13e8c 100644
--- a/arch/x86/kernel/cpu/mce/internal.h
+++ b/arch/x86/kernel/cpu/mce/internal.h
@@ -49,6 +49,8 @@ void intel_init_cmci(void);
 void intel_init_lmce(void);
 void intel_clear_lmce(void);
 bool intel_filter_mce(struct mce *m);
+bool intel_cmci_poll_lock(void);
+void intel_cmci_poll_unlock(bool locked);
 #else
 # define cmci_intel_adjust_timer mce_adjust_timer_default
 static inline bool mce_intel_cmci_poll(void) { return false; }
@@ -58,6 +60,8 @@ static inline void intel_init_cmci(void) { }
 static inline void intel_init_lmce(void) { }
 static inline void intel_clear_lmce(void) { }
 static inline bool intel_filter_mce(struct mce *m) { return false; }
+static inline bool intel_cmci_poll_lock(void) { return false; }
+static inline void intel_cmci_poll_unlock(bool locked) { }
 #endif
 
 void mce_timer_kick(unsigned long interval);
-- 
Aristeu