linux-kernel - Re: [PATCH v11 3/8] powerpc/perf: consolidate read_user_stack

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Message-Id: <1585039473.da4762n2s0.astroid@bobo.none>
Date:   Tue, 24 Mar 2020 18:48:20 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     linuxppc-dev@...ts.ozlabs.org, Michal Suchanek <msuchanek@...e.de>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Allison Randal <allison@...utok.net>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Claudio Carvalho <cclaudio@...ux.ibm.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        "David S. Miller" <davem@...emloft.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Eric Richter <erichte@...ux.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Gustavo Luiz Duarte <gustavold@...ux.ibm.com>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Jordan Niethe <jniethe5@...il.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Michael Neuling <mikey@...ling.org>,
        Ingo Molnar <mingo@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Namhyung Kim <namhyung@...nel.org>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Rob Herring <robh@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <valentin.schneider@....com>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v11 3/8] powerpc/perf: consolidate read_user_stack_32

Michal Suchanek's on March 19, 2020 10:19 pm:
> There are two almost identical copies for 32bit and 64bit.
> 
> The function is used only in 32bit code which will be split out in next
> patch so consolidate to one function.
> 
> Signed-off-by: Michal Suchanek <msuchanek@...e.de>
> Reviewed-by: Christophe Leroy <christophe.leroy@....fr>
> ---
> v6:  new patch
> v8:  move the consolidated function out of the ifdef block.
> v11: rebase on top of def0bfdbd603
> ---
>  arch/powerpc/perf/callchain.c | 48 +++++++++++++++++------------------
>  1 file changed, 24 insertions(+), 24 deletions(-)
> 
> diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c
> index cbc251981209..c9a78c6e4361 100644
> --- a/arch/powerpc/perf/callchain.c
> +++ b/arch/powerpc/perf/callchain.c
> @@ -161,18 +161,6 @@ static int read_user_stack_64(unsigned long __user *ptr, unsigned long *ret)
>  	return read_user_stack_slow(ptr, ret, 8);
>  }
>  
> -static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
> -{
> -	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
> -	    ((unsigned long)ptr & 3))
> -		return -EFAULT;
> -
> -	if (!probe_user_read(ret, ptr, sizeof(*ret)))
> -		return 0;
> -
> -	return read_user_stack_slow(ptr, ret, 4);
> -}
> -
>  static inline int valid_user_sp(unsigned long sp, int is_64)
>  {
>  	if (!sp || (sp & 7) || sp > (is_64 ? TASK_SIZE : 0x100000000UL) - 32)
> @@ -277,19 +265,9 @@ static void perf_callchain_user_64(struct perf_callchain_entry_ctx *entry,
>  }
>  
>  #else  /* CONFIG_PPC64 */
> -/*
> - * On 32-bit we just access the address and let hash_page create a
> - * HPTE if necessary, so there is no need to fall back to reading
> - * the page tables.  Since this is called at interrupt level,
> - * do_page_fault() won't treat a DSI as a page fault.
> - */
> -static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
> +static int read_user_stack_slow(void __user *ptr, void *buf, int nb)
>  {
> -	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
> -	    ((unsigned long)ptr & 3))
> -		return -EFAULT;
> -
> -	return probe_user_read(ret, ptr, sizeof(*ret));
> +	return 0;
>  }
>  
>  static inline void perf_callchain_user_64(struct perf_callchain_entry_ctx *entry,
> @@ -312,6 +290,28 @@ static inline int valid_user_sp(unsigned long sp, int is_64)
>  
>  #endif /* CONFIG_PPC64 */
>  
> +/*
> + * On 32-bit we just access the address and let hash_page create a
> + * HPTE if necessary, so there is no need to fall back to reading
> + * the page tables.  Since this is called at interrupt level,
> + * do_page_fault() won't treat a DSI as a page fault.
> + */

The comment is actually probably better to stay in the 32-bit
read_user_stack_slow implementation. Is that function defined
on 32-bit purely so that you can use IS_ENABLED()? In that case
I would prefer to put a BUG() there which makes it self documenting.

Thanks,
Nick

> +static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
> +{
> +	int rc;
> +
> +	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
> +	    ((unsigned long)ptr & 3))
> +		return -EFAULT;
> +
> +	rc = probe_user_read(ret, ptr, sizeof(*ret));
> +
> +	if (IS_ENABLED(CONFIG_PPC64) && rc)
> +		return read_user_stack_slow(ptr, ret, 4);
> +
> +	return rc;
> +}
> +
>  /*
>   * Layout for non-RT signal frames
>   */
> -- 
> 2.23.0
> 
>