Re: [PATCH v4 4/9] mm/vmalloc: BUG_ON() on an unaligned range in vmap_pages_range_noflush_walk()

[Uladzislau Rezki <urezki@gmail.com>]

On Tue, Nov 10, 2026 at 07:25:41PM +0800, Hao Ge wrote:
> The pte loop of vmap_pages_pte_range() maps whole pages and stops
> only when addr lands exactly on end.  An unaligned end lets addr
> jump over it and the loop keeps mapping into whatever follows the
> range.  An unaligned start maps the page below the range with its
> first pte.  That corruption is impossible to debug afterwards, so
> bug out on addr and end at the entry of
> vmap_pages_range_noflush_walk().
> 
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Signed-off-by: Hao Ge <hao.ge@linux.dev>
> ---
>  mm/vmalloc.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 27f2674a5556..86fbb1d2b27a 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -698,6 +698,8 @@ static int vmap_pages_range_noflush_walk(unsigned long addr, unsigned long end,
>  	pgtbl_mod_mask mask = 0;
>  
>  	BUG_ON(addr >= end);
> +	BUG_ON(!PAGE_ALIGNED(addr) || !PAGE_ALIGNED(end));
> +
>
But why do we add this? We used to live without it and as far i see
we have not gotten any report about any unaligned addresses un-maping.

The vmap allocator grantees that va->va_start/end have to be page
aligned.

--
Uladzislau Rezki