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Date: Thu, 19 Mar 2020 15:04:16 +0100
From: Michal =?iso-8859-1?Q?Such=E1nek?= <msuchanek@suse.de>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Subject: Re: [PATCH v11 4/8] powerpc/perf: consolidate valid_user_sp
Message-ID: <20200319140416.GK25468@kitsune.suse.cz>
References: <cover.1584613649.git.msuchanek@suse.de>
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Cc: Mark Rutland <mark.rutland@arm.com>,
 Gustavo Luiz Duarte <gustavold@linux.ibm.com>,
 Peter Zijlstra <peterz@infradead.org>,
 Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
 Paul Mackerras <paulus@samba.org>, Jiri Olsa <jolsa@redhat.com>,
 Rob Herring <robh@kernel.org>, Michael Neuling <mikey@neuling.org>,
 Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
 Masahiro Yamada <masahiroy@kernel.org>, Nayna Jain <nayna@linux.ibm.com>,
 "linux-fsdevel @ vger . kernel . org --in-reply-to="
 <20200225173541.1549955-1-npiggin@gmail.com>,
 Alexander Shishkin <alexander.shishkin@linux.intel.com>,
 Ingo Molnar <mingo@redhat.com>, Allison Randal <allison@lohutok.net>,
 Jordan Niethe <jniethe5@gmail.com>,
 Valentin Schneider <valentin.schneider@arm.com>, Arnd Bergmann <arnd@arndb.de>,
 Arnaldo Carvalho de Melo <acme@kernel.org>,
 Alexander Viro <viro@zeniv.linux.org.uk>,
 Jonathan Cameron <Jonathan.Cameron@huawei.com>,
 Namhyung Kim <namhyung@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
 Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
 Hari Bathini <hbathini@linux.ibm.com>,
 Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 Nicholas Piggin <npiggin@gmail.com>, Claudio Carvalho <cclaudio@linux.ibm.com>,
 Eric Richter <erichte@linux.ibm.com>,
 "Eric W. Biederman" <ebiederm@xmission.com>,
 "open list:LINUX FOR POWERPC PA SEMI PWRFICIENT"
 <linuxppc-dev@lists.ozlabs.org>, "David S. Miller" <davem@davemloft.net>,
 Thiago Jung Bauermann <bauerman@linux.ibm.com>
Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org
Sender: "Linuxppc-dev"
 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

On Thu, Mar 19, 2020 at 03:35:03PM +0200, Andy Shevchenko wrote:
> On Thu, Mar 19, 2020 at 1:54 PM Michal Suchanek <msuchanek@suse.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);
Sounds reasonale.

Thanks

Michal
> 
> -- 
> With Best Regards,
> Andy Shevchenko