linux-kernel - Re: [PATCH v7 11/16] mm/highmem: introduce clear_user

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Message-ID: <6626d497-4c27-4263-9be1-1c05d2672019@redhat.com>
Date: Tue, 23 Sep 2025 10:06:51 +0200
From: David Hildenbrand <david@...hat.com>
To: Ankur Arora <ankur.a.arora@...cle.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, x86@...nel.org
Cc: akpm@...ux-foundation.org, bp@...en8.de, dave.hansen@...ux.intel.com,
 hpa@...or.com, mingo@...hat.com, mjguzik@...il.com, luto@...nel.org,
 peterz@...radead.org, acme@...nel.org, namhyung@...nel.org,
 tglx@...utronix.de, willy@...radead.org, raghavendra.kt@....com,
 boris.ostrovsky@...cle.com, konrad.wilk@...cle.com
Subject: Re: [PATCH v7 11/16] mm/highmem: introduce clear_user_highpages()

On 17.09.25 17:24, Ankur Arora wrote:
> Define clear_user_highpages() which clears pages sequentially using
> the single page variant.
> 
> With !CONFIG_HIGHMEM, pages are contiguous so use the range clearing
> primitive clear_user_pages().
> 
> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
> ---
>   include/linux/highmem.h | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)
> 
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index 6234f316468c..ed609987e24d 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -207,6 +207,24 @@ static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
>   }
>   #endif
>   
> +#ifndef clear_user_highpages

Maybe we can add a simple kernel doc that points at the doc of clear_user_pages,
but makes it clear that this for pages that might reside in highmem.

> +static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
> +					unsigned int npages)
> +{
> +	if (!IS_ENABLED(CONFIG_HIGHMEM)) {
> +		clear_user_pages(base, vaddr, page, npages);

Single line should work

		clear_user_pages(page_address(page), vaddr, page, npages);

> +		return;
> +	}
> +
> +	do {
> +		clear_user_highpage(page, vaddr);
> +		vaddr += PAGE_SIZE;
> +		page++;
> +	} while (--npages);
> +}
> +#endif
> +
>   #ifndef vma_alloc_zeroed_movable_folio
>   /**
>    * vma_alloc_zeroed_movable_folio - Allocate a zeroed page for a VMA.


-- 
Cheers

David / dhildenb