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

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Message-ID: <4e061f4f-cd57-4df4-a001-9eba80d1ded9@redhat.com>
Date: Wed, 24 Sep 2025 13:06:42 +0200
From: David Hildenbrand <david@...hat.com>
To: Ankur Arora <ankur.a.arora@...cle.com>
Cc: 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 v7 11/16] mm/highmem: introduce clear_user_highpages()

On 23.09.25 22:34, Ankur Arora wrote:
> 
> David Hildenbrand <david@...hat.com> writes:
> 
>> 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.
> 
> Didn't add one because clear_user_highpage() didn't have one. Will add
> for both.
> 

Doesn't have to be excessive. But even I have to keep reminding myself 
when to use clear_page(), clear_user_page(), clear_user_highpage() ...

>>> +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);
> 
> Unfortunately not. The problem is that I'm defining the fallback version
> of clear_user_pages() as a macro in the previous patch.

Yet another sign that we have to fix that instead. :)

-- 
Cheers

David / dhildenb