x86/irq: Suppress unlikely interrupt stats by default

Unlikely interrupt counters like the spurious vector and the synthetic APIC
ICR read retry show up in /proc/interrupts with all counts 0 most of the
time.

As these are events which should never happen, suppress them by default and
enable them for output when they actually happen.

This requires a seperate bitmap as the description array is marked
__ro_after_init. With that bitmap in place it becomes RO data.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Radu Rendec <radu@rendec.net>
Link: https://patch.msgid.link/20260517194931.276486277@kernel.org

4 files changed, 31 insertions, 12 deletions

diff --git a/arch/x86/include/asm/hardirq.h b/arch/x86/include/asm/hardirq.h
index 423fa4d068a7..6723b512c694 100644
--- a/arch/x86/include/asm/hardirq.h
+++ b/arch/x86/include/asm/hardirq.h
@@ -68,6 +68,7 @@ DECLARE_PER_CPU_ALIGNED(struct pi_desc, posted_msi_pi_desc);
 #define __ARCH_IRQ_STAT
 
 #define inc_irq_stat(index)	this_cpu_inc(irq_stat.counts[IRQ_COUNT_##index])
+void irq_stat_inc_and_enable(enum irq_stat_counts which);
 
 #ifdef CONFIG_X86_LOCAL_APIC
 #define inc_perf_irq_stat()	inc_irq_stat(APIC_PERF)
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 6599e8004d94..e27c263d6c13 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -2114,7 +2114,7 @@ static noinline void handle_spurious_interrupt(u8 vector)
 
 	trace_spurious_apic_entry(vector);
 
-	inc_irq_stat(SPURIOUS);
+	irq_stat_inc_and_enable(IRQ_COUNT_SPURIOUS);
 
 	/*
 	 * If this is a spurious interrupt then do not acknowledge
diff --git a/arch/x86/kernel/apic/ipi.c b/arch/x86/kernel/apic/ipi.c
index 3635c4d7b7f5..c627bee3b14f 100644
--- a/arch/x86/kernel/apic/ipi.c
+++ b/arch/x86/kernel/apic/ipi.c
@@ -120,7 +120,7 @@ u32 apic_mem_wait_icr_idle_timeout(void)
 	for (cnt = 0; cnt < 1000; cnt++) {
 		if (!(apic_read(APIC_ICR) & APIC_ICR_BUSY))
 			return 0;
-		inc_irq_stat(ICR_READ_RETRY);
+		irq_stat_inc_and_enable(IRQ_COUNT_ICR_READ_RETRY);
 		udelay(100);
 	}
 	return APIC_ICR_BUSY;
diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index decd08d3d315..2d8ca4116610 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -68,19 +68,24 @@ struct irq_stat_info {
 	const char	*text;
 };
 
+#define DEFAULT_SUPPRESSED_VECTOR	UINT_MAX
+
 #define ISS(idx, sym, txt) [IRQ_COUNT_##idx] = { .symbol = sym, .text = txt }
 
 #define ITS(idx, sym, txt) [IRQ_COUNT_##idx] =				\
 	{ .skip_vector = idx## _VECTOR, .symbol = sym, .text = txt }
 
-static struct irq_stat_info irq_stat_info[IRQ_COUNT_MAX] __ro_after_init = {
+#define IDS(idx, sym, txt) [IRQ_COUNT_##idx] =				\
+	{ .skip_vector = DEFAULT_SUPPRESSED_VECTOR, .symbol = sym, .text = txt }
+
+static const struct irq_stat_info irq_stat_info[IRQ_COUNT_MAX] = {
 	ISS(NMI,			"NMI",	"  Non-maskable interrupts\n"),
 #ifdef CONFIG_X86_LOCAL_APIC
 	ISS(APIC_TIMER,			"LOC",	"  Local timer interrupts\n"),
-	ISS(SPURIOUS,			"SPU",	"  Spurious interrupts\n"),
+	IDS(SPURIOUS,			"SPU",	"  Spurious interrupts\n"),
 	ISS(APIC_PERF,			"PMI",	"  Performance monitoring interrupts\n"),
 	ISS(IRQ_WORK,			"IWI",	"  IRQ work interrupts\n"),
-	ISS(ICR_READ_RETRY,		"RTR",	"  APIC ICR read retries\n"),
+	IDS(ICR_READ_RETRY,		"RTR",	"  APIC ICR read retries\n"),
 	ISS(X86_PLATFORM_IPI,		"PLT",	"  Platform interrupts\n"),
 #endif
 #ifdef CONFIG_SMP
@@ -121,34 +126,47 @@ static struct irq_stat_info irq_stat_info[IRQ_COUNT_MAX] __ro_after_init = {
 #endif
 };
 
+static DECLARE_BITMAP(irq_stat_count_show, IRQ_COUNT_MAX) __read_mostly;
+
 static int __init irq_init_stats(void)
 {
-	struct irq_stat_info *info = irq_stat_info;
+	const struct irq_stat_info *info = irq_stat_info;
 
 	for (unsigned int i = 0; i < ARRAY_SIZE(irq_stat_info); i++, info++) {
-		if (info->skip_vector && test_bit(info->skip_vector, system_vectors))
-			info->skip_vector = 0;
+		if (!info->skip_vector || (info->skip_vector != DEFAULT_SUPPRESSED_VECTOR &&
+					   test_bit(info->skip_vector, system_vectors)))
+			set_bit(i, irq_stat_count_show);
 	}
 
 #ifdef CONFIG_X86_LOCAL_APIC
 	if (!x86_platform_ipi_callback)
-		irq_stat_info[IRQ_COUNT_X86_PLATFORM_IPI].skip_vector = 1;
+		clear_bit(IRQ_COUNT_X86_PLATFORM_IPI, irq_stat_count_show);
 #endif
 
 #ifdef CONFIG_X86_POSTED_MSI
 	if (!posted_msi_enabled())
-		irq_stat_info[IRQ_COUNT_POSTED_MSI_NOTIFICATION].skip_vector = 1;
+		clear_bit(IRQ_COUNT_POSTED_MSI_NOTIFICATION, irq_stat_count_show);
 #endif
 
 #ifdef CONFIG_X86_MCE_AMD
 	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
 	    boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
-		irq_stat_info[IRQ_COUNT_DEFERRED_ERROR].skip_vector = 1;
+		clear_bit(IRQ_COUNT_DEFERRED_ERROR, irq_stat_count_show);
 #endif
 	return 0;
 }
 late_initcall(irq_init_stats);
 
+/*
+ * Used for default disabled counters to increment the stats and to enable the
+ * entry for /proc/interrupts output.
+ */
+void irq_stat_inc_and_enable(enum irq_stat_counts which)
+{
+	this_cpu_inc(irq_stat.counts[which]);
+	set_bit(which, irq_stat_count_show);
+}
+
 #ifdef CONFIG_PROC_FS
 /*
  * /proc/interrupts printing for arch specific interrupts
@@ -158,7 +176,7 @@ int arch_show_interrupts(struct seq_file *p, int prec)
 	const struct irq_stat_info *info = irq_stat_info;
 
 	for (unsigned int i = 0; i < ARRAY_SIZE(irq_stat_info); i++, info++) {
-		if (info->skip_vector)
+		if (!test_bit(i, irq_stat_count_show))
 			continue;
 
 		seq_printf(p, "%*s:", prec, info->symbol);