linux-kernel - Re: [PATCH v4 2/9] mm: add atomic VMA flags and set VM_MAYBE

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Message-ID: <9b18ee75-bf06-46d7-96f3-395cb159217b@kernel.org>
Date: Wed, 19 Nov 2025 10:06:39 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Jonathan Corbet <corbet@....net>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
 Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
 Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
 Lance Yang <lance.yang@...ux.dev>, linux-kernel@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, Andrei Vagin <avagin@...il.com>
Subject: Re: [PATCH v4 2/9] mm: add atomic VMA flags and set VM_MAYBE_GUARD as
 such

On 18.11.25 11:17, Lorenzo Stoakes wrote:
> This patch adds the ability to atomically set VMA flags with only the mmap
> read/VMA read lock held.
> 
> As this could be hugely problematic for VMA flags in general given that
> all other accesses are non-atomic and serialised by the mmap/VMA locks, we
> implement this with a strict allow-list - that is, only designated flags
> are allowed to do this.
> 
> We make VM_MAYBE_GUARD one of these flags.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Reviewed-by: Pedro Falcato <pfalcato@...e.de>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
> ---

IIUC all other flag modifications need a write lock, so this should just 
work.

Acked-by: David Hildenbrand (Red Hat) <david@...nel.org>

-- 
Cheers

David