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

[Dev Jain]

On 29/03/25 4:20 am, Mike Rapoport wrote:
> 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.

Sorry, mistakenly used them interchangeably. I'll fix this.

> > 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>

Thanks!

> >   	 * 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