rdmsr_on_cpu, wrmsr_on_cpu

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().

Dave Jones mentioned cpufreq might be not only user of rdmsr_on_cpu() and
wrmsr_on_cpu(), so I'm putting them into arch/{i386,x86_64}/lib/ .

Signed-off-by: Alexey Dobriyan <adobriyan@openvz.org>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Jones <davej@redhat.com>

2 files changed, 72 insertions, 0 deletions

diff --git a/arch/i386/lib/Makefile b/arch/i386/lib/Makefile
index d86a548b8d54..0d41223472c2 100644
--- a/arch/i386/lib/Makefile
+++ b/arch/i386/lib/Makefile
@@ -7,3 +7,5 @@ lib-y = checksum.o delay.o usercopy.o getuser.o putuser.o memcpy.o strstr.o \
         bitops.o semaphore.o
 
 lib-$(CONFIG_X86_USE_3DNOW) += mmx.o
+
+obj-y = msr-on-cpu.o
diff --git a/arch/i386/lib/msr-on-cpu.c b/arch/i386/lib/msr-on-cpu.c
new file mode 100644
index 000000000000..2092ea15ba85
--- /dev/null
+++ b/arch/i386/lib/msr-on-cpu.c
@@ -0,0 +1,70 @@
+#include <linux/module.h>
+#include <linux/preempt.h>
+#include <linux/smp.h>
+#include <asm/msr.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);