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    SubjectRe: [patch] bug in cpuid & msr on nosmp machine
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    Date
    On Thu, 2004-05-20 at 17:32, Andrew Morton wrote:
    > I think what you want here is
    >
    > if (!cpu_possible(cpu) || !cpu_online(cpu))
    > return -ENXIO;

    It works, but it's not really correct. cpu_possible() is correct, but
    cpu_online() might no longer be true by the time do_cpu_read() calls
    do_cpu_id().

    One way would be to do lock_cpu_hotplug() in cpuid_open() and introduce
    a cpuid_close() which would do unlock_cpu_hotplug(). Another would be
    to drop the check here, and fail the actual read. A final way is to do
    no checks, in which case it becomes a noop if the cpu is offline.

    > --- 25/arch/i386/kernel/cpuid.c~cpuid-msr-range-checking-fix 2004-05-20 00:30:21.812166544 -0700
    > +++ 25-akpm/arch/i386/kernel/cpuid.c 2004-05-20 00:31:16.607836336 -0700
    > @@ -133,10 +133,12 @@ static ssize_t cpuid_read(struct file *f
    > static int cpuid_open(struct inode *inode, struct file *file)
    > {
    > int cpu = iminor(file->f_dentry->d_inode);
    > - struct cpuinfo_x86 *c = &(cpu_data)[cpu];
    > + struct cpuinfo_x86 *c;
    >
    > - if (!cpu_online(cpu))
    > + if (!cpu_possible(cpu) || !cpu_online(cpu))
    > return -ENXIO; /* No such CPU */
    > +
    > + c = &(cpu_data)[cpu];
    > if (c->cpuid_level < 0)
    > return -EIO; /* CPUID not supported */
    >
    > diff -puN arch/i386/kernel/msr.c~cpuid-msr-range-checking-fix arch/i386/kernel/msr.c
    > --- 25/arch/i386/kernel/msr.c~cpuid-msr-range-checking-fix 2004-05-20 00:30:21.836162896 -0700
    > +++ 25-akpm/arch/i386/kernel/msr.c 2004-05-20 00:31:56.952702984 -0700
    > @@ -239,10 +239,12 @@ static ssize_t msr_write(struct file * f
    > static int msr_open(struct inode *inode, struct file *file)
    > {
    > int cpu = iminor(file->f_dentry->d_inode);
    > - struct cpuinfo_x86 *c = &(cpu_data)[cpu];
    > -
    > - if (!cpu_online(cpu))
    > - return -ENXIO; /* No such CPU */
    > + struct cpuinfo_x86 *c;
    > +
    > + if (!cpu_possible(cpu) || !cpu_online(cpu))
    > + return -ENXIO; /* No such CPU */
    > +
    > + c = &(cpu_data)[cpu];
    > if ( !cpu_has(c, X86_FEATURE_MSR) )
    > return -EIO; /* MSR not supported */
    >
    >
    > _
    --
    Anyone who quotes me in their signature is an idiot -- Rusty Russell

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