linux-kernel - Re: [PATCH v2 1/3] introduce memcpy

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Date:   Wed, 26 Oct 2016 22:51:53 +0300
From:   Boaz Harrosh <boaz@...xistor.com>
To:     Brian Boylston <brian.boylston@....com>, linux-nvdimm@...ts.01.org
CC:     oliver.moreno@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 1/3] introduce memcpy_nocache()

On 10/26/2016 06:50 PM, Brian Boylston wrote:
> Introduce memcpy_nocache() as a memcpy() that avoids the processor cache
> if possible.  Without arch-specific support, this defaults to just
> memcpy().  For now, include arch-specific support for x86.
> 
> Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: <x86@...nel.org>
> Cc: Al Viro <viro@...IV.linux.org.uk>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Brian Boylston <brian.boylston@....com>
> Reviewed-by: Toshi Kani <toshi.kani@....com>
> Reported-by: Oliver Moreno <oliver.moreno@....com>
> ---
>  arch/x86/include/asm/string_32.h |  3 +++
>  arch/x86/include/asm/string_64.h |  3 +++
>  arch/x86/lib/misc.c              | 12 ++++++++++++
>  include/linux/string.h           | 15 +++++++++++++++
>  4 files changed, 33 insertions(+)
> 
> diff --git a/arch/x86/include/asm/string_32.h b/arch/x86/include/asm/string_32.h
> index 3d3e835..64f80c0 100644
> --- a/arch/x86/include/asm/string_32.h
> +++ b/arch/x86/include/asm/string_32.h
> @@ -196,6 +196,9 @@ static inline void *__memcpy3d(void *to, const void *from, size_t len)
>  
>  #endif
>  
> +#define __HAVE_ARCH_MEMCPY_NOCACHE
> +extern void *memcpy_nocache(void *dest, const void *src, size_t count);
> +
>  #define __HAVE_ARCH_MEMMOVE
>  void *memmove(void *dest, const void *src, size_t n);
>  
> diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h
> index 90dbbd9..a8fdd55 100644
> --- a/arch/x86/include/asm/string_64.h
> +++ b/arch/x86/include/asm/string_64.h
> @@ -51,6 +51,9 @@ extern void *__memcpy(void *to, const void *from, size_t len);
>  #define memcpy(dst, src, len) __inline_memcpy((dst), (src), (len))
>  #endif
>  
> +#define __HAVE_ARCH_MEMCPY_NOCACHE
> +extern void *memcpy_nocache(void *dest, const void *src, size_t count);
> +
>  #define __HAVE_ARCH_MEMSET
>  void *memset(void *s, int c, size_t n);
>  void *__memset(void *s, int c, size_t n);
> diff --git a/arch/x86/lib/misc.c b/arch/x86/lib/misc.c
> index 76b373a..c993ab3 100644
> --- a/arch/x86/lib/misc.c
> +++ b/arch/x86/lib/misc.c
> @@ -1,3 +1,6 @@
> +#include <linux/export.h>
> +#include <linux/uaccess.h>
> +
>  /*
>   * Count the digits of @val including a possible sign.
>   *
> @@ -19,3 +22,12 @@ int num_digits(int val)
>  	}
>  	return d;
>  }
> +
> +#ifdef __HAVE_ARCH_MEMCPY_NOCACHE
> +void *memcpy_nocache(void *dest, const void *src, size_t count)
> +{
> +	__copy_from_user_inatomic_nocache(dest, src, count);
> +	return dest;
> +}
> +EXPORT_SYMBOL(memcpy_nocache);
> +#endif
> diff --git a/include/linux/string.h b/include/linux/string.h
> index 26b6f6a..7f40c41 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -102,6 +102,21 @@ extern void * memset(void *,int,__kernel_size_t);
>  #ifndef __HAVE_ARCH_MEMCPY
>  extern void * memcpy(void *,const void *,__kernel_size_t);
>  #endif
> +
> +#ifndef __HAVE_ARCH_MEMCPY_NOCACHE
> +/**
> + * memcpy_nocache - Copy one area of memory to another, avoiding the
> + * processor cache if possible
> + * @dest: Where to copy to
> + * @src: Where to copy from
> + * @count: The size of the area.
> + */
> +static inline void *memcpy_nocache(void *dest, const void *src, size_t count)
> +{
> +	return memcpy(dest, src, count);
> +}

What about memcpy_to_pmem() in linux/pmem.h it already has all the arch switches.

Feels bad to add yet just another arch switch over __copy_user_nocache

Just feels like too many things that do the same thing. Sigh

Boaz

> +#endif
> +
>  #ifndef __HAVE_ARCH_MEMMOVE
>  extern void * memmove(void *,const void *,__kernel_size_t);
>  #endif
>