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rdmsr_on_cpu, wrmsr_on_cpu

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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>
This commit is contained in:
Alexey Dobriyan
2007-02-16 01:48:11 -08:00
committed by Dave Jones
parent 22f7bb0329
commit b077ffb3b7
6 changed files with 79 additions and 1 deletions
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70
arch/i386/lib/msr-on-cpu.c Normal file
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#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);