Re: [PATCH v7 12/16] arm: mm: define clear_user_highpages()

[David Hildenbrand]

On 24.09.25 00:25, Ankur Arora wrote:
> David Hildenbrand <david@xxxxxxxxxx> writes:
>
> > On 17.09.25 17:24, Ankur Arora wrote:
> > > For configurations with CONFIG_MMU we do not define clear_user_page().
> > > This runs into issues for configurations with !CONFIG_HIGHMEM, because
> > > clear_user_highpages() expects to clear_user_page() (via a default
> > > version of clear_user_pages()).
> >
> > I'm confused. Can you elaborate once more why we cannot take care of that in
> > common code?
>
> So my definition of clear_user_highpages,
>
>      +#ifndef clear_user_highpages
>      +static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
>      +					unsigned int npages)
>      +{
>      +	if (!IS_ENABLED(CONFIG_HIGHMEM)) {
>      +		void *base = page_address(page);
>      +		clear_user_pages(base, vaddr, page, npages);
>      +		return;
>      +	}
>      +
>      +	do {
>      +		clear_user_highpage(page, vaddr);
>      +		vaddr += PAGE_SIZE;
>      +		page++;
>      +	} while (--npages);
>      +}
>      +#endif
>
> assumes one of the following:
>
>    1. clear_user_highpages is defined by the architecture or,
>    2. HIGHMEM => arch defines clear_user_highpage or clear_user_page
>    3. !HIGHMEM => arch defines clear_user_pages or clear_user_page
>
> Case 2 is fine, since ARM has clear_user_highpage().
>
> Case 3 runs into a problem since ARM doesn't have clear_user_pages()
> or clear_user_page() (it does have the second, but only with !CONFIG_MMU).

I think we should look into having a generic fallback version in common 
code instead for that case, and not require the arch to implement such a 
loop around clear_user_highpage().

--
Cheers

David / dhildenb