linux-kernel - Re: [PATCH v4 4/9] mm: implement sticky VMA flags

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <f8669e93-24a8-47e1-9ba9-66df9627e998@kernel.org>
Date: Fri, 21 Nov 2025 17:09:08 +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 4/9] mm: implement sticky VMA flags

On 11/18/25 11:17, Lorenzo Stoakes wrote:
> It is useful to be able to designate that certain flags are 'sticky', that
> is, if two VMAs are merged one with a flag of this nature and one without,
> the merged VMA sets this flag.
> 
> As a result we ignore these flags for the purposes of determining VMA flag
> differences between VMAs being considered for merge.
> 
> This patch therefore updates the VMA merge logic to perform this action,
> with flags possessing this property being described in the VM_STICKY
> bitmap.
> 
> Those flags which ought to be ignored for the purposes of VMA merge are
> described in the VM_IGNORE_MERGE bitmap, which the VMA merge logic is also
> updated to use.
> 
> As part of this change we place VM_SOFTDIRTY in VM_IGNORE_MERGE as it
> already had this behaviour, alongside VM_STICKY as sticky flags by
> implication must not disallow merge.
> 
> Ultimately it seems that we should make VM_SOFTDIRTY a sticky flag in its
> own right, but this change is out of scope for this series.
> 
> The only sticky flag designated as such is VM_MAYBE_GUARD, so as a result
> of this change, once the VMA flag is set upon guard region installation,
> VMAs with guard ranges will now not have their merge behaviour impacted as
> a result and can be freely merged with other VMAs without VM_MAYBE_GUARD
> set.
> 
> Also update the comments for vma_modify_flags() to directly reference
> sticky flags now we have established the concept.
> 
> We also update the VMA userland tests to account for the changes.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Reviewed-by: Pedro Falcato <pfalcato@...e.de>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
> ---

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

-- 
Cheers

David