linux-kernel - Re: [PATCH v6 12/12] mm: constify highmem related functions for improved const-correctness

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Message-ID: <12bb3414-2ca8-4384-80e5-81889f2bd35f@redhat.com>
Date: Tue, 2 Sep 2025 10:11:04 +0200
From: David Hildenbrand <david@...hat.com>
To: Max Kellermann <max.kellermann@...os.com>, akpm@...ux-foundation.org,
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Subject: Re: [PATCH v6 12/12] mm: constify highmem related functions for
 improved const-correctness

On 01.09.25 22:50, Max Kellermann wrote:
> Lots of functions in mm/highmem.c do not write to the given pointers
> and do not call functions that take non-const pointers and can
> therefore be constified.
> 
> This includes functions like kunmap() which might be implemented in a
> way that writes to the pointer (e.g. to update reference counters or
> mapping fields), but currently are not.
> 
> kmap() on the other hand cannot be made const because it calls
> set_page_address() which is non-const in some
> architectures/configurations.

Right, we store the address in page->virtual.

It's interesting that kumap() won't set that field to NULL. That seems 
to happen in flush_all_zero_pkmaps(). And we seem to flush during kmap() 
in case we have to empty slots.

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers

David / dhildenb