linux-kernel - Re: [PATCH 0/3] selftests: Remove duplicate CPUID wrappers

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Date:   Mon, 7 Feb 2022 11:00:49 -0700
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Reinette Chatre <reinette.chatre@...el.com>, shuah@...nel.org,
        linux-kselftest@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ram Pai <linuxram@...ibm.com>,
        Sandipan Das <sandipan@...ux.ibm.com>,
        Florian Weimer <fweimer@...hat.com>,
        "Desnes A. Nunes do Rosario" <desnesn@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Suchanek <msuchanek@...e.de>, linux-mm@...ck.org,
        "Chang S . Bae" <chang.seok.bae@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 0/3] selftests: Remove duplicate CPUID wrappers

On 2/4/22 5:11 PM, Reinette Chatre wrote:
> Hi Shuah,
> 
> On 2/4/2022 3:39 PM, Shuah Khan wrote:
>> On 2/4/22 12:17 PM, Reinette Chatre wrote:
>>> A few tests that require running CPUID do so with a private
>>> implementation of a wrapper for CPUID. This duplication of
>>> the CPUID wrapper should be avoided but having one is also
>>> unnecessary because of the existence of a macro that can
>>> be used instead.
>>>
>>> This series replaces private CPUID wrappers with calls
>>> to the __cpuid_count() macro from cpuid.h as made available
>>> by gcc and clang/llvm.
>>>
>>> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
>>> Cc: Ram Pai <linuxram@...ibm.com>
>>> Cc: Sandipan Das <sandipan@...ux.ibm.com>
>>> Cc: Florian Weimer <fweimer@...hat.com>
>>> Cc: "Desnes A. Nunes do Rosario" <desnesn@...ux.vnet.ibm.com>
>>> Cc: Ingo Molnar <mingo@...nel.org>
>>> Cc: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
>>> Cc: Michael Ellerman <mpe@...erman.id.au>
>>> Cc: Michal Suchanek <msuchanek@...e.de>
>>> Cc: linux-mm@...ck.org
>>> Cc: Chang S. Bae <chang.seok.bae@...el.com>
>>> Cc: Borislav Petkov <bp@...e.de>
>>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>> Cc: Ingo Molnar <mingo@...hat.com>
>>> Cc: "H. Peter Anvin" <hpa@...or.com>
>>> Cc: x86@...nel.org
>>> Cc: Andy Lutomirski <luto@...nel.org>
>>>
>>> Reinette Chatre (3):
>>>     selftests/vm/pkeys: Use existing __cpuid_count() macro
>>>     selftests/x86/amx: Use existing __cpuid_count() macro
>>>     selftests/x86/corrupt_xstate_header: Use existing __cpuid_count()
>>>       macro
>>>
>>>    tools/testing/selftests/vm/pkey-x86.h         | 22 +++---------------
>>>    tools/testing/selftests/x86/amx.c             | 23 +++++--------------
>>>    .../selftests/x86/corrupt_xstate_header.c     | 17 ++------------
>>>    3 files changed, 11 insertions(+), 51 deletions(-)
>>>
>>
>> I am all for this cleanup. However, I am not finding __cpuid_count()
>> marco on my system with gcc:
>>
>> gcc --version
>> gcc (Ubuntu 11.2.0-7ubuntu2) 11.2.0
>>
>> My concern is regression on older gcc versions.
> 
> Please see this message from our earlier thread where you were able
> to find it on your system:
> https://lore.kernel.org/linux-kselftest/63293c72-55ca-9446-35eb-74aff4c8ba5d@linuxfoundation.org/
> 

Right. After I sent off the response, I was thinking we discussed
this before. Thanks for the refresh.

> As mentioned in that thread, on my system it arrived via user space's
> libgcc-dev package. This does not seem to be the first time including
> files from this source - I did a quick check and from what I can tell
> existing kselftest includes like stdarg.h, stdbool.h, stdatomic.h,
> unwind.h, x86intrin.h ... arrive via libgcc-dev.
> 

This will work fine on newer versions of gcc/clang. However this could
fail when mainline kselftest is used on stable releases on test rings
and so on, especially if they have older versions of gcc/clang.

We will have to find a solution for this. Instead of deleting the local
define, let's keep it under ifndef __cpuid_count

/usr/lib/gcc/x86_64-linux-gnu/11/include/cpuid.h

#define __cpuid_count(level, count, a, b, c, d)                         \
   __asm__ __volatile__ ("cpuid\n\t"                                     \
                         : "=a" (a), "=b" (b), "=c" (c), "=d" (d)        \
                         : "0" (level), "2" (count))

thanks,
-- Shuah