x86 mmiotrace: dynamically disable non-boot CPUs
From 8979ee55cb6a429c4edd72ebec2244b849f6a79a Mon Sep 17 00:00:00 2001
From: Pekka Paalanen <pq@iki.fi>
Date: Sat, 12 Apr 2008 00:18:57 +0300
Mmiotrace is not reliable with multiple CPUs and may
miss events. Drop to single CPU when mmiotrace is activated.
Signed-off-by: Pekka Paalanen <pq@iki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/mm/mmio-mod.c b/arch/x86/mm/mmio-mod.c
index 6d6cac8..1f77d85 100644
--- a/arch/x86/mm/mmio-mod.c
+++ b/arch/x86/mm/mmio-mod.c
@@ -32,6 +32,7 @@
#include <asm/e820.h> /* for ISA_START_ADDRESS */
#include <asm/atomic.h>
#include <linux/percpu.h>
+#include <linux/cpu.h>
#include "pf_in.h"
@@ -400,6 +401,64 @@
}
}
+#ifdef CONFIG_HOTPLUG_CPU
+static cpumask_t downed_cpus;
+
+static void enter_uniprocessor(void)
+{
+ int cpu;
+ int err;
+
+ get_online_cpus();
+ downed_cpus = cpu_online_map;
+ cpu_clear(first_cpu(cpu_online_map), downed_cpus);
+ if (num_online_cpus() > 1)
+ pr_notice(NAME "Disabling non-boot CPUs...\n");
+ put_online_cpus();
+
+ for_each_cpu_mask(cpu, downed_cpus) {
+ err = cpu_down(cpu);
+ if (!err) {
+ pr_info(NAME "CPU%d is down.\n", cpu);
+ } else {
+ pr_err(NAME "Error taking CPU%d down: %d\n", cpu, err);
+ }
+ }
+ if (num_online_cpus() > 1)
+ pr_warning(NAME "multiple CPUs still online, "
+ "may miss events.\n");
+}
+
+static void leave_uniprocessor(void)
+{
+ int cpu;
+ int err;
+
+ if (cpus_weight(downed_cpus) == 0)
+ return;
+ pr_notice(NAME "Re-enabling CPUs...\n");
+ for_each_cpu_mask(cpu, downed_cpus) {
+ err = cpu_up(cpu);
+ if (!err)
+ pr_info(NAME "enabled CPU%d.\n", cpu);
+ else
+ pr_err(NAME "cannot re-enable CPU%d: %d\n", cpu, err);
+ }
+}
+
+#else /* !CONFIG_HOTPLUG_CPU */
+static void enter_uniprocessor(void)
+{
+ if (num_online_cpus() > 1)
+ pr_warning(NAME "multiple CPUs are online, may miss events. "
+ "Suggest booting with maxcpus=1 kernel argument.\n");
+}
+
+static void leave_uniprocessor(void)
+{
+}
+#endif
+
#if 0 /* XXX: out of order */
static struct file_operations fops_marker = {
.owner = THIS_MODULE,
@@ -422,6 +481,7 @@
if (nommiotrace)
pr_info(NAME "MMIO tracing disabled.\n");
+ enter_uniprocessor();
spin_lock_irq(&trace_lock);
atomic_inc(&mmiotrace_enabled);
spin_unlock_irq(&trace_lock);
@@ -442,6 +502,7 @@
spin_unlock_irq(&trace_lock);
clear_trace_list(); /* guarantees: no more kmmio callbacks */
+ leave_uniprocessor();
if (marker_file) {
debugfs_remove(marker_file);
marker_file = NULL;