linux-kernel - Re: [PATCH v8 3/7] mm/highmem: introduce clear_user

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Message-ID: <bd11e906-8d01-4e39-b385-f158520b589b@kernel.org>
Date: Fri, 7 Nov 2025 09:48:37 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
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 v8 3/7] mm/highmem: introduce clear_user_highpages()

On 27.10.25 21:21, 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>
> 
> Note: fixed

That should be dropped.

> ---
>   include/linux/highmem.h | 29 +++++++++++++++++++++++++++++
>   1 file changed, 29 insertions(+)
> 
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index 105cc4c00cc3..c5f8b1556fd7 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -199,6 +199,11 @@ static inline void invalidate_kernel_vmap_range(void *vaddr, int size)
>   
>   /* when CONFIG_HIGHMEM is not set these will be plain clear/copy_page */
>   #ifndef clear_user_highpage
> +/**
> + * clear_user_highpage() - clear a page to be mapped to user space
> + * @page: start page
> + * @vaddr: start address of the user mapping
> + */
>   static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
>   {
>   	void *addr = kmap_local_page(page);
> @@ -207,6 +212,30 @@ static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
>   }
>   #endif
>   
> +/**
> + * clear_user_highpages() - clear a page range to be mapped to user space
> + * @page: start page
> + * @vaddr: start address of the user mapping
> + * @npages: number of pages
> + *
> + * Assumes that all the pages in the region (@page, +@...ges) are valid
> + * so this does no exception handling.
> + */
> +static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
> +					unsigned int npages)
> +{
> +	if (!IS_ENABLED(CONFIG_HIGHMEM)) {
> +		clear_user_pages(page_address(page), vaddr, page, npages);
> +		return;
> +	}
> +
> +	do {
> +		clear_user_highpage(page, vaddr);
> +		vaddr += PAGE_SIZE;
> +		page++;
> +	} while (--npages);
> +}
> +
>   #ifndef vma_alloc_zeroed_movable_folio
>   /**
>    * vma_alloc_zeroed_movable_folio - Allocate a zeroed page for a VMA.

Acked-by: David Hildenbrand (Red Hat) <david@...nel.org>

-- 
Cheers

David