linux-kernel - Re: [PATCH RFC 33/35] kfence: drop nth

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Message-ID: <b09b7ef4-5b06-4bb8-9be3-1194e3904c92@redhat.com>
Date: Thu, 21 Aug 2025 23:45:18 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Alexander Potapenko <glider@...gle.com>, Marco Elver <elver@...gle.com>,
 Dmitry Vyukov <dvyukov@...gle.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Brendan Jackman <jackmanb@...gle.com>,
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 Jason Gunthorpe <jgg@...dia.com>, Jens Axboe <axboe@...nel.dk>,
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 kasan-dev@...glegroups.com, kvm@...r.kernel.org,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>, linux-arm-kernel@...s.com,
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Subject: Re: [PATCH RFC 33/35] kfence: drop nth_page() usage

On 21.08.25 22:32, David Hildenbrand wrote:
> On 21.08.25 22:06, David Hildenbrand wrote:
>> We want to get rid of nth_page(), and kfence init code is the last user.
>>
>> Unfortunately, we might actually walk a PFN range where the pages are
>> not contiguous, because we might be allocating an area from memblock
>> that could span memory sections in problematic kernel configs (SPARSEMEM
>> without SPARSEMEM_VMEMMAP).
>>
>> We could check whether the page range is contiguous
>> using page_range_contiguous() and failing kfence init, or making kfence
>> incompatible these problemtic kernel configs.
>>
>> Let's keep it simple and simply use pfn_to_page() by iterating PFNs.
>>
> 
> Fortunately this series is RFC due to lack of detailed testing :P
> 
> Something gives me a NULL-pointer pointer here (maybe the virt_to_phys()).
> 
> Will look into that tomorrow.

Okay, easy: relying on i but not updating it /me facepalm

-- 
Cheers

David / dhildenb