2022-06-06 14:31:00

by Fabio M. De Francesco

Subject: [PATCH] mm/highmem: Delete memmove_page()

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 <[email protected]>
Cc: Ira Weiny <[email protected]>
Signed-off-by: Fabio M. De Francesco <[email protected]>
---
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

2022-06-06 14:55:54

by Baoquan He

Subject: Re: [PATCH] mm/highmem: Delete memmove_page()

On 06/06/22 at 04:15pm, 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.

Nice clean up.
Reviewed-by: Baoquan He <[email protected]>

>
> Reported-by: Matthew Wilcox <[email protected]>
> Cc: Ira Weiny <[email protected]>
> Signed-off-by: Fabio M. De Francesco <[email protected]>
> ---
> 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
>
>

2022-06-06 15:12:33

by Ira Weiny

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 <[email protected]>
> Cc: Ira Weiny <[email protected]>

Reviewed-by: Ira Weiny <[email protected]>

> Signed-off-by: Fabio M. De Francesco <[email protected]>
> ---
> 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
>