Re: [RFC PATCH] mm/highmem: VM_BUG_ON() if offset + len > PAGE_SIZE

Fabio M. De Francesco
2022-04-25T01:47:49Z

On domenica 24 aprile 2022 12:48:06 CEST Fabio M. De Francesco wrote:
> Call VM_BUG_ON() if offset + len > PAGE_SIZE.
>
> This is an RFC patch because I'm not sure if we actually need to
BUG_ON(),

Actually I considered VM_BUG_ON() for consistency with the other functions
in highmem.h

What about VM_WARN_ON_ONCE() here and also in memset_page?

Thanks,

Fabio

> so I'd like to know what Maintainers and other developers think about
this
> proposal.
>
> Please note that memset_page() uses VM_BUG_ON() to prevent the same
issue.
>
> Furthermore, I also cannot understand why memset_page() does not call
> flush_dcache_page() after memset() but I suppose that the different
> implementations of these two functions should be addressed in another
RFC.
>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> ---
> include/linux/highmem.h | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index c3d562b5f0c1..bdb16d5f8148 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -349,6 +349,8 @@ static inline void memcpy_to_page(struct page *page,
size_t offset,
> static inline void memzero_page(struct page *page, size_t offset, size_t
len)
> {
> char *addr = kmap_local_page(page);
> +
> + VM_BUG_ON(offset + len > PAGE_SIZE);
> memset(addr + offset, 0, len);
> flush_dcache_page(page);
> kunmap_local(addr);
> --
> 2.34.1
>
>