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

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Message-ID: <CAHp75VcMkPeJ6exroipnxvf-7g-C8QbVm0bAnp=rk505_nxySw@mail.gmail.com>
Date:   Thu, 19 Mar 2020 15:35:03 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     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>,
        Christophe Leroy <christophe.leroy@....fr>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnd Bergmann <arnd@...db.de>,
        Nayna Jain <nayna@...ux.ibm.com>,
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        Claudio Carvalho <cclaudio@...ux.ibm.com>,
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        Hari Bathini <hbathini@...ux.ibm.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
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        Michael Neuling <mikey@...ling.org>,
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        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

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:

  unsigned long align = is_32bit_task() ? 3 : 7;
  unsigned long top = STACK_TOP - (is_32bit_task() ? 16 : 32);

  return !(!sp || (sp & align) || sp > top);

-- 
With Best Regards,
Andy Shevchenko