Re: [PATCH v4 5/9] mm/vmalloc: BUG_ON() on an unaligned range in __vunmap_range_noflush()

[Uladzislau Rezki <urezki@gmail.com>]

On Tue, Nov 10, 2026 at 07:25:42PM +0800, Hao Ge wrote:
> The PTE loop of the unmap path stops only at addr == end.  With an
> unaligned end addr never lands on end, so the loop walks past the
> range and keeps clearing.  With an unaligned start the loop begins
> in the page containing start, which extends below the range.  Either
> way the unmap clears the mappings adjacent to the range, and that is
> nearly impossible to debug afterwards.
> 
> vmap only installs page-aligned, page-granular mappings, so an
> unaligned unmap request is never a legitimate teardown, and there is
> no way to tell which pages the caller meant.  Check addr and end at
> the entry of __vunmap_range_noflush() and bug out before any PTE is
> cleared.
> 
> 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 86fbb1d2b27a..0565cbfe325c 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -518,6 +518,8 @@ void __vunmap_range_noflush(unsigned long start, unsigned long end)
>  	pgtbl_mod_mask mask = 0;
>  
>  	BUG_ON(addr >= end);
> +	BUG_ON(!PAGE_ALIGNED(addr) || !PAGE_ALIGNED(end));
> +
>  	pgd = pgd_offset_k(addr);
>  	do {
>  		next = pgd_addr_end(addr, end);
> -- 
> 2.25.1
> 
I am not sure this is good to stop machine at all. WARN_ON_ONCE()
and return?

--
Uladzislau Rezki