linux-kernel - Re: [PATCH] mm/highmem: Delete memmove

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Date:   Mon, 6 Jun 2022 07:58:37 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH] mm/highmem: Delete memmove_page()

On Mon, Jun 06, 2022 at 04:15:33PM +0200, Fabio M. De Francesco wrote:
> Matthew Wilcox reported that, while he was looking at memmove_page(), he
> realized that it can't actually work.
> 
> The reasons are hidden in its implementation, which makes use of
> memmove() on logical addresses provided by kmap_local_page(). memmove()
> does the wrong thing when it tests "if (dest <= src)".
> 
> Therefore, delete memmove_page().
> 
> No need to change any other code because we have no call sites of
> memmove_page() across the whole kernel.
> 
> Reported-by: Matthew Wilcox <willy@...radead.org>
> Cc: Ira Weiny <ira.weiny@...el.com>

Reviewed-by: Ira Weiny <ira.weiny@...el.com>

> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> ---
>  include/linux/highmem.h | 13 -------------
>  1 file changed, 13 deletions(-)
> 
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index 3af34de54330..fee9835e3793 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -336,19 +336,6 @@ static inline void memcpy_page(struct page *dst_page, size_t dst_off,
>  	kunmap_local(dst);
>  }
>  
> -static inline void memmove_page(struct page *dst_page, size_t dst_off,
> -			       struct page *src_page, size_t src_off,
> -			       size_t len)
> -{
> -	char *dst = kmap_local_page(dst_page);
> -	char *src = kmap_local_page(src_page);
> -
> -	VM_BUG_ON(dst_off + len > PAGE_SIZE || src_off + len > PAGE_SIZE);
> -	memmove(dst + dst_off, src + src_off, len);
> -	kunmap_local(src);
> -	kunmap_local(dst);
> -}
> -
>  static inline void memset_page(struct page *page, size_t offset, int val,
>  			       size_t len)
>  {
> -- 
> 2.36.1
>