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

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Message-ID: <874ir2cq0d.fsf@oracle.com>
Date: Sun, 09 Nov 2025 23:20:50 -0800
From: Ankur Arora <ankur.a.arora@...cle.com>
To: "David Hildenbrand (Red Hat)" <david@...nel.org>
Cc: Ankur Arora <ankur.a.arora@...cle.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org, 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()


David Hildenbrand (Red Hat) <david@...nel.org> writes:

> 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>

Thanks (for this and the others.)

--
ankur