Re: [PATCH v3 3/3] x86,arch_prctl Add ARCH_[GET|SET]_CPUID for controlling the CPUID instruction

From	Kyle Huey <me@kylehuey.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v3 3/3] x86,arch_prctl Add ARCH_[GET\|SET]_CPUID for controlling the CPUID instruction
Date	2016-09-16 07:40 +0200
Message-ID	<shU2t-nt-7@gated-at.bofh.it> (permalink)
References	<shOq5-56k-3@gated-at.bofh.it> <shOq5-56k-7@gated-at.bofh.it> <shOT8-5wV-31@gated-at.bofh.it>
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On Thu, Sep 15, 2016 at 5:07 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Thu, Sep 15, 2016 at 4:33 PM, Kyle Huey <me@kylehuey.com> wrote:
>> +int get_cpuid_mode(unsigned long adr)
>> +{
>> +       unsigned int val;
>> +
>> +       if (test_thread_flag(TIF_NOCPUID))
>> +               val = ARCH_CPUID_SIGSEGV;
>> +       else
>> +               val = ARCH_CPUID_ENABLE;
>> +
>> +       return put_user(val, (unsigned int __user *)adr);
>> +}
>
> Can we just do:
>
> if (arg2 != 0)
>   return -EINVAL;
> else
>  return test_thread_flag(TIF_NOCPUID) ? ARCH_CPUID_SIGSEGBV : ARCH_CPUID_ENABLE;

We could.  I copied the pattern of PR_GET_TSC here, but I don't feel
strongly about it.

>> diff --git a/tools/testing/selftests/x86/cpuid-fault.c b/tools/testing/selftests/x86/cpuid-fault.c
>> new file mode 100644
>> index 0000000..a9f3f68
>> --- /dev/null
>> +++ b/tools/testing/selftests/x86/cpuid-fault.c
>> @@ -0,0 +1,234 @@
>> +
>> +/*
>> + * Tests for arch_prctl(ARCH_GET_CPUID, ...) / prctl(ARCH_SET_CPUID, ...)
>> + *
>> + * Basic test to test behaviour of ARCH_GET_CPUID and ARCH_SET_CPUID
>> + */
>> +
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <unistd.h>
>> +#include <signal.h>
>> +#include <inttypes.h>
>> +#include <cpuid.h>
>> +#include <errno.h>
>> +#include <sys/wait.h>
>> +
>> +#include <sys/prctl.h>
>> +#include <linux/prctl.h>
>> +
>> +const char *cpuid_names[] = {
>> +       [0] = "[not set]",
>
> Is 0 even possible?

Only if the call fails.

- Kyle

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[PATCH v3] arch_prctl,x86 Add ARCH_[GET|SET]_CPUID for controlling the CPUID instruction Kyle Huey <me@kylehuey.com> - 2016-09-16 01:40 +0200
  [PATCH v3 2/3] x86 Test and expose CPUID faulting capabilities in /proc/cpuinfo Kyle Huey <me@kylehuey.com> - 2016-09-16 01:40 +0200
    Re: [PATCH v3 2/3] x86 Test and expose CPUID faulting capabilities in /proc/cpuinfo Andy Lutomirski <luto@amacapital.net> - 2016-09-16 01:50 +0200
    Re: [PATCH v3 2/3] x86 Test and expose CPUID faulting capabilities  in /proc/cpuinfo Thomas Gleixner <tglx@linutronix.de> - 2016-09-16 12:20 +0200
  [PATCH v3 3/3] x86,arch_prctl Add ARCH_[GET|SET]_CPUID for controlling the CPUID instruction Kyle Huey <me@kylehuey.com> - 2016-09-16 01:40 +0200
    Re: [PATCH v3 3/3] x86,arch_prctl Add ARCH_[GET|SET]_CPUID for  controlling the CPUID instruction Andy Lutomirski <luto@amacapital.net> - 2016-09-16 02:10 +0200
      Re: [PATCH v3 3/3] x86,arch_prctl Add ARCH_[GET|SET]_CPUID for  controlling the CPUID instruction Kyle Huey <me@kylehuey.com> - 2016-09-16 07:40 +0200

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