Re: [PATCH 07/32] kmsan: Remove a useless assignment from kmsan_vmap_pages_range_noflush()

Alexander Potapenko
2023-11-16T10:52:52Z

On Wed, Nov 15, 2023 at 9:34 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote:
>
> The value assigned to prot is immediately overwritten on the next line
> with PAGE_KERNEL. The right hand side of the assignment has no
> side-effects.
>
> Fixes: b073d7f8aee4 ("mm: kmsan: maintain KMSAN metadata for page operations")
> Suggested-by: Alexander Gordeev <agordeev@linux.ibm.com>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@google.com>

> ---
> mm/kmsan/shadow.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c
> index b9d05aff313e..2d57408c78ae 100644
> --- a/mm/kmsan/shadow.c
> +++ b/mm/kmsan/shadow.c
> @@ -243,7 +243,6 @@ int kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,
> s_pages[i] = shadow_page_for(pages[i]);
> o_pages[i] = origin_page_for(pages[i]);
> }
> - prot = __pgprot(pgprot_val(prot) | _PAGE_NX);
> prot = PAGE_KERNEL;

This bug dates back to 5.1-rc2, when KMSAN didn't exist upstream.
The commit introducing vmap support already had it:
https://github.com/google/kmsan/commit/3ff9d7c640d378485286e1a99d85984ae6901f23
I don't remember what exactly required the more relaxed PAGE_KERNEL
mask though :)