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Date:   Tue, 24 Mar 2020 18:48:20 +1000
From:   Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v11 3/8] powerpc/perf: consolidate read_user_stack_32
To:     linuxppc-dev@lists.ozlabs.org, Michal Suchanek <msuchanek@suse.de>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
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Michal Suchanek's on March 19, 2020 10:19 pm:
> There are two almost identical copies for 32bit and 64bit.
>=20
> The function is used only in 32bit code which will be split out in next
> patch so consolidate to one function.
>=20
> Signed-off-by: Michal Suchanek <msuchanek@suse.de>
> Reviewed-by: Christophe Leroy <christophe.leroy@c-s.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(-)
>=20
> 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);
>  }
> =20
> -static int read_user_stack_32(unsigned int __user *ptr, unsigned int *re=
t)
> -{
> -	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_callc=
hain_entry_ctx *entry,
>  }
> =20
>  #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 *re=
t)
> +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;
>  }
> =20
>  static inline void perf_callchain_user_64(struct perf_callchain_entry_ct=
x *entry,
> @@ -312,6 +290,28 @@ static inline int valid_user_sp(unsigned long sp, in=
t is_64)
> =20
>  #endif /* CONFIG_PPC64 */
> =20
> +/*
> + * 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 *re=
t)
> +{
> +	int rc;
> +
> +	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
> +	    ((unsigned long)ptr & 3))
> +		return -EFAULT;
> +
> +	rc =3D 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
>   */
> --=20
> 2.23.0
>=20
>=20
=