linux-kernel - Re: [PATCH v11 4/8] powerpc/perf: consolidate valid_user

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Message-ID: <8775f299-be1b-3457-c59d-e4f61d8223e5@c-s.fr>
Date:   Thu, 19 Mar 2020 15:16:03 +0100
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Michal Suchanek <msuchanek@...e.de>
Cc:     "open list:LINUX FOR POWERPC PA SEMI PWRFICIENT" 
        <linuxppc-dev@...ts.ozlabs.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnd Bergmann <arnd@...db.de>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Eric Richter <erichte@...ux.ibm.com>,
        Claudio Carvalho <cclaudio@...ux.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Valentin Schneider <valentin.schneider@....com>,
        Jordan Niethe <jniethe5@...il.com>,
        Michael Neuling <mikey@...ling.org>,
        Gustavo Luiz Duarte <gustavold@...ux.ibm.com>,
        Allison Randal <allison@...utok.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-fsdevel @ vger . kernel . org --in-reply-to=" 
        <20200225173541.1549955-1-npiggin@...il.com>
Subject: Re: [PATCH v11 4/8] powerpc/perf: consolidate valid_user_sp



Le 19/03/2020 à 14:35, Andy Shevchenko a écrit :
> On Thu, Mar 19, 2020 at 1:54 PM Michal Suchanek <msuchanek@...e.de> wrote:
>>
>> Merge the 32bit and 64bit version.
>>
>> Halve the check constants on 32bit.
>>
>> Use STACK_TOP since it is defined.
>>
>> Passing is_64 is now redundant since is_32bit_task() is used to
>> determine which callchain variant should be used. Use STACK_TOP and
>> is_32bit_task() directly.
>>
>> This removes a page from the valid 32bit area on 64bit:
>>   #define TASK_SIZE_USER32 (0x0000000100000000UL - (1 * PAGE_SIZE))
>>   #define STACK_TOP_USER32 TASK_SIZE_USER32
> 
> ...
> 
>> +static inline int valid_user_sp(unsigned long sp)
>> +{
>> +       bool is_64 = !is_32bit_task();
>> +
>> +       if (!sp || (sp & (is_64 ? 7 : 3)) || sp > STACK_TOP - (is_64 ? 32 : 16))
>> +               return 0;
>> +       return 1;
>> +}
> 
> Perhaps better to read
> 
>    if (!sp)
>      return 0;
> 
>    if (is_32bit_task()) {
>      if (sp & 0x03)
>        return 0;
>      if (sp > STACK_TOP - 16)
>        return 0;
>    } else {
>      ...
>    }
> 
>    return 1;
> 
> Other possibility:

I prefer this one.

> 
>    unsigned long align = is_32bit_task() ? 3 : 7;

I would call it mask instead of align

>    unsigned long top = STACK_TOP - (is_32bit_task() ? 16 : 32);
> 
>    return !(!sp || (sp & align) || sp > top);
> 

Christophe