Re: [PATCH] arm64: pageattr: Explicitly bail out when changing permissions for vmalloc_huge mappings

[Mike Rapoport]

On Fri, Mar 28, 2025 at 11:51:03AM +0530, Dev Jain wrote:
> arm64 uses apply_to_page_range to change permissions for kernel VA mappings,

                                                     for vmalloc mappings ^

arm64 does not allow changing permissions to any VA address right now.

> which does not support changing permissions for leaf mappings. This function
> will change permissions until it encounters a leaf mapping, and will bail
> out. To avoid this partial change, explicitly disallow changing permissions
> for VM_ALLOW_HUGE_VMAP mappings.
> 
> Signed-off-by: Dev Jain <dev.jain@xxxxxxx>
> ---
>  arch/arm64/mm/pageattr.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index 39fd1f7ff02a..8337c88eec69 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -96,7 +96,7 @@ static int change_memory_common(unsigned long addr, int numpages,
>  	 * we are operating on does not result in such splitting.
>  	 *
>  	 * Let's restrict ourselves to mappings created by vmalloc (or vmap).
> -	 * Those are guaranteed to consist entirely of page mappings, and
> +	 * Disallow VM_ALLOW_HUGE_VMAP vmalloc mappings so that

I'd keep mention of page mappings in the comment, e.g

	* Disallow VM_ALLOW_HUGE_VMAP mappings to guarantee that only page
	* mappings are updated and splitting is never needed.

With this and changelog updates Ryan asked for

Reviewed-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>


>  	 * splitting is never needed.
>  	 *
>  	 * So check whether the [addr, addr + size) interval is entirely
> @@ -105,7 +105,7 @@ static int change_memory_common(unsigned long addr, int numpages,
>  	area = find_vm_area((void *)addr);
>  	if (!area ||
>  	    end > (unsigned long)kasan_reset_tag(area->addr) + area->size ||
> -	    !(area->flags & VM_ALLOC))
> +	    ((area->flags & (VM_ALLOC | VM_ALLOW_HUGE_VMAP)) != VM_ALLOC))
>  		return -EINVAL;
>  
>  	if (!numpages)
> -- 
> 2.30.2
> 

-- 
Sincerely yours,
Mike.