linux-kernel - Re: [PATCH 2/5] userfaultfd, shmem: use a VMA callback to handle UFFDIO

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Message-ID: <a06e57ff-b77b-44fd-9b69-929d7647644b@kernel.org>
Date: Mon, 24 Nov 2025 12:03:17 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Mike Rapoport <rppt@...nel.org>, linux-mm@...ck.org
Cc: Andrea Arcangeli <aarcange@...hat.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Axel Rasmussen <axelrasmussen@...gle.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>, Hugh Dickins
 <hughd@...gle.com>, James Houghton <jthoughton@...gle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Michal Hocko
 <mhocko@...e.com>, Nikita Kalyazin <kalyazin@...zon.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Peter Xu <peterx@...hat.com>,
 Sean Christopherson <seanjc@...gle.com>, Shuah Khan <shuah@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Vlastimil Babka <vbabka@...e.cz>,
 linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 2/5] userfaultfd, shmem: use a VMA callback to handle
 UFFDIO_CONTINUE

On 11/23/25 11:27, Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>
> 
> When userspace resolves a page fault in a shmem VMA with UFFDIO_CONTINUE
> it needs to get a folio that already exists in the pagecache backing
> that VMA.
> 
> Instead of using shmem_get_folio() for that, add a get_pagecache_folio()

get_shared_folio()

Given that the helper now no longer receives a VMA, I assume we can just 
really call it get_folio() and the "shared" part would be implicit. 
(from the inode)

> method to 'struct vm_operations_struct' that will return a folio if it
> exists in the VMA's pagecache at given pgoff.
> 
> Implement get_pagecache_folio() method for shmem and slightly refactor
> userfaultfd's mfill_atomic() and mfill_atomic_pte_continue() to support
> this new API.
> 
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> ---

Nothing else jumped at me :)

-- 
Cheers

David