rdmsr_on_cpu, wrmsr_on_cpu et al

rdmsr_on_cpu, wrmsr_on_cpu et al

[Alexey Dobriyan]

Hi, Dave!

There was OpenVZ specific bug rendering some cpufreq drivers unusable
on SMP. In short, when cpufreq code thinks it confined itself to
needed cpu by means of set_cpus_allowed() to execute rdmsr, some
"virtual cpu" feature can migrate process to anywhere. This triggers
bugons and does wrong things in general.

This got fixed by introducing rdmsr_on_cpu and wrmsr_on_cpu executing
rdmsr and wrmsr on given physical cpu by means of smp_call_function_single().

So, understanding p4-clockmod is not the only driver that was affected,
is something like this acceptable for start?


 arch/i386/kernel/cpu/cpufreq/Makefile      |    2
 arch/i386/kernel/cpu/cpufreq/msr-on-cpu.c  |   71 +++++++++++++++++++++++++++++
 arch/i386/kernel/cpu/cpufreq/msr-on-cpu.h  |    9 +++
 arch/i386/kernel/cpu/cpufreq/p4-clockmod.c |   31 ++----------
 4 files changed, 88 insertions(+), 25 deletions(-)

--- a/arch/i386/kernel/cpu/cpufreq/Makefile
+++ b/arch/i386/kernel/cpu/cpufreq/Makefile
@@ -11,5 +11,5 @@ obj-$(CONFIG_X86_SPEEDSTEP_LIB)		+= spee
 obj-$(CONFIG_X86_SPEEDSTEP_SMI)		+= speedstep-smi.o
 obj-$(CONFIG_X86_ACPI_CPUFREQ)		+= acpi-cpufreq.o
 obj-$(CONFIG_X86_SPEEDSTEP_CENTRINO)	+= speedstep-centrino.o
-obj-$(CONFIG_X86_P4_CLOCKMOD)		+= p4-clockmod.o
+obj-$(CONFIG_X86_P4_CLOCKMOD)		+= p4-clockmod.o msr-on-cpu.o
 obj-$(CONFIG_X86_CPUFREQ_NFORCE2)	+= cpufreq-nforce2.o
--- /dev/null
+++ b/arch/i386/kernel/cpu/cpufreq/msr-on-cpu.c
@@ -0,0 +1,71 @@
+#include <linux/module.h>
+#include <linux/preempt.h>
+#include <linux/smp.h>
+#include <asm/msr.h>
+#include "msr-on-cpu.h"
+
+#ifdef CONFIG_SMP
+struct msr_info {
+	u32 msr_no;
+	u32 l, h;
+};
+
+static void __rdmsr_on_cpu(void *info)
+{
+	struct msr_info *rv = info;
+
+	rdmsr(rv->msr_no, rv->l, rv->h);
+}
+
+void rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h)
+{
+	preempt_disable();
+	if (smp_processor_id() == cpu)
+		rdmsr(msr_no, *l, *h);
+	else {
+		struct msr_info rv;
+
+		rv.msr_no = msr_no;
+		smp_call_function_single(cpu, __rdmsr_on_cpu, &rv, 0, 1);
+		*l = rv.l;
+		*h = rv.h;
+	}
+	preempt_enable();
+}
+
+static void __wrmsr_on_cpu(void *info)
+{
+	struct msr_info *rv = info;
+
+	wrmsr(rv->msr_no, rv->l, rv->h);
+}
+
+void wrmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h)
+{
+	preempt_disable();
+	if (smp_processor_id() == cpu)
+		wrmsr(msr_no, l, h);
+	else {
+		struct msr_info rv;
+
+		rv.msr_no = msr_no;
+		rv.l = l;
+		rv.h = h;
+		smp_call_function_single(cpu, __wrmsr_on_cpu, &rv, 0, 1);
+	}
+	preempt_enable();
+}
+#else
+void rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h)
+{
+	rdmsr(msr_no, *l, *h);
+}
+
+void wrmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h)
+{
+	wrmsr(msr_no, l, h);
+}
+#endif
+
+EXPORT_SYMBOL(rdmsr_on_cpu);
+EXPORT_SYMBOL(wrmsr_on_cpu);
--- /dev/null
+++ b/arch/i386/kernel/cpu/cpufreq/msr-on-cpu.h
@@ -0,0 +1,9 @@
+#ifndef __MSR_ON_CPU_H__
+#define __MSR_ON_CPU_H__
+
+#include <linux/types.h>
+
+void rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h);
+void wrmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h);
+
+#endif
--- a/arch/i386/kernel/cpu/cpufreq/p4-clockmod.c
+++ b/arch/i386/kernel/cpu/cpufreq/p4-clockmod.c
@@ -33,6 +33,7 @@ #include <asm/processor.h>
 #include <asm/msr.h>
 #include <asm/timex.h>
 
+#include "msr-on-cpu.h"
 #include "speedstep-lib.h"
 
 #define PFX	"p4-clockmod: "
@@ -63,7 +64,7 @@ static int cpufreq_p4_setdc(unsigned int
 	if (!cpu_online(cpu) || (newstate > DC_DISABLE) || (newstate == DC_RESV))
 		return -EINVAL;
 
-	rdmsr(MSR_IA32_THERM_STATUS, l, h);
+	rdmsr_on_cpu(cpu, MSR_IA32_THERM_STATUS, &l, &h);
 
 	if (l & 0x01)
 		dprintk("CPU#%d currently thermal throttled\n", cpu);
@@ -71,10 +72,10 @@ static int cpufreq_p4_setdc(unsigned int
 	if (has_N44_O17_errata[cpu] && (newstate == DC_25PT || newstate == DC_DFLT))
 		newstate = DC_38PT;
 
-	rdmsr(MSR_IA32_THERM_CONTROL, l, h);
+	rdmsr_on_cpu(cpu, MSR_IA32_THERM_CONTROL, &l, &h);
 	if (newstate == DC_DISABLE) {
 		dprintk("CPU#%d disabling modulation\n", cpu);
-		wrmsr(MSR_IA32_THERM_CONTROL, l & ~(1<<4), h);
+		wrmsr_on_cpu(cpu, MSR_IA32_THERM_CONTROL, l & ~(1<<4), h);
 	} else {
 		dprintk("CPU#%d setting duty cycle to %d%%\n",
 			cpu, ((125 * newstate) / 10));
@@ -85,7 +86,7 @@ static int cpufreq_p4_setdc(unsigned int
 		 */
 		l = (l & ~14);
 		l = l | (1<<4) | ((newstate & 0x7)<<1);
-		wrmsr(MSR_IA32_THERM_CONTROL, l, h);
+		wrmsr_on_cpu(cpu, MSR_IA32_THERM_CONTROL, l, h);
 	}
 
 	return 0;
@@ -112,7 +113,6 @@ static int cpufreq_p4_target(struct cpuf
 {
 	unsigned int    newstate = DC_RESV;
 	struct cpufreq_freqs freqs;
-	cpumask_t cpus_allowed;
 	int i;
 
 	if (cpufreq_frequency_table_target(policy, &p4clockmod_table[0], target_freq, relation, &newstate))
@@ -133,17 +133,8 @@ static int cpufreq_p4_target(struct cpuf
 	/* run on each logical CPU, see section 13.15.3 of IA32 Intel Architecture Software
 	 * Developer's Manual, Volume 3
 	 */
-	cpus_allowed = current->cpus_allowed;
-
-	for_each_cpu_mask(i, policy->cpus) {
-		cpumask_t this_cpu = cpumask_of_cpu(i);
-
-		set_cpus_allowed(current, this_cpu);
-		BUG_ON(smp_processor_id() != i);
-
+	for_each_cpu_mask(i, policy->cpus)
 		cpufreq_p4_setdc(i, p4clockmod_table[newstate].index);
-	}
-	set_cpus_allowed(current, cpus_allowed);
 
 	/* notifiers */
 	for_each_cpu_mask(i, policy->cpus) {
@@ -265,17 +256,9 @@ static int cpufreq_p4_cpu_exit(struct cp
 
 static unsigned int cpufreq_p4_get(unsigned int cpu)
 {
-	cpumask_t cpus_allowed;
 	u32 l, h;
 
-	cpus_allowed = current->cpus_allowed;
-
-	set_cpus_allowed(current, cpumask_of_cpu(cpu));
-	BUG_ON(smp_processor_id() != cpu);
-
-	rdmsr(MSR_IA32_THERM_CONTROL, l, h);
-
-	set_cpus_allowed(current, cpus_allowed);
+	rdmsr_on_cpu(cpu, MSR_IA32_THERM_CONTROL, &l, &h);
 
 	if (l & 0x10) {
 		l = l >> 1;

Re: rdmsr_on_cpu, wrmsr_on_cpu et al

[Dave Jones]

On Wed, Jan 17, 2007 at 04:26:13PM +0300, Alexey Dobriyan wrote:
 > Hi, Dave!
 > 
 > There was OpenVZ specific bug rendering some cpufreq drivers unusable
 > on SMP. In short, when cpufreq code thinks it confined itself to
 > needed cpu by means of set_cpus_allowed() to execute rdmsr, some
 > "virtual cpu" feature can migrate process to anywhere. This triggers
 > bugons and does wrong things in general.
 > 
 > This got fixed by introducing rdmsr_on_cpu and wrmsr_on_cpu executing
 > rdmsr and wrmsr on given physical cpu by means of smp_call_function_single().
 > 
 > So, understanding p4-clockmod is not the only driver that was affected,
 > is something like this acceptable for start?

This is probably useful outside of cpufreq too, so should probably
go somewhere in include/asm/processor.h for eg.
Looks ok on a quick glance, but I'd like to see if anyone on lkml
has any comments, especially the usual x86/x86-64 experts.

		Dave

-- 
http://www.codemonkey.org.uk