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

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Message-ID: <877bxnayrc.fsf@oracle.com>
Date: Wed, 24 Sep 2025 22:26:31 -0700
From: Ankur Arora <ankur.a.arora@...cle.com>
To: David Hildenbrand <david@...hat.com>
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 v7 11/16] mm/highmem: introduce clear_user_highpages()


David Hildenbrand <david@...hat.com> writes:

> 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() ...

And now all the multi-page variants. Really motivates the removal of
the HIGHMEM stuff.

>>>> +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. :)

Yeah :).

Thanks
--
ankur