linux-kernel - Re: [PATCH v3 0/4] move all VMA allocation, freeing and duplication logic to mm

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Message-ID: <044b4684-4b88-4228-9bf6-31491b7738ba@suse.cz>
Date: Tue, 29 Apr 2025 09:28:05 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: "Liam R . Howlett" <Liam.Howlett@...cle.com>, Jann Horn
 <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
 David Hildenbrand <david@...hat.com>, Kees Cook <kees@...nel.org>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Suren Baghdasaryan <surenb@...gle.com>, linux-mm@...ck.org,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/4] move all VMA allocation, freeing and duplication
 logic to mm

On 4/28/25 17:28, Lorenzo Stoakes wrote:
> Currently VMA allocation, freeing and duplication exist in kernel/fork.c,
> which is a violation of separation of concerns, and leaves these functions
> exposed to the rest of the kernel when they are in fact internal
> implementation details.
> 
> Resolve this by moving this logic to mm, and making it internal to vma.c,
> vma.h.
> 
> This also allows us, in future, to provide userland testing around this
> functionality.
> 
> We additionally abstract dup_mmap() to mm, being careful to ensure
> kernel/fork.c acceses this via the mm internal header so it is not exposed
> elsewhere in the kernel.
> 
> As part of this change, also abstract initial stack allocation performed in
> __bprm_mm_init() out of fs code into mm via the create_init_stack_vma(), as
> this code uses vm_area_alloc() and vm_area_free().
> 
> In order to do so sensibly, we introduce a new mm/vma_exec.c file, which
> contains the code that is shared by mm and exec. This file is added to both
> memory mapping and exec sections in MAINTAINERS so both sets of maintainers
> can maintain oversight.

Note that kernel/fork.c itself belongs to no section. Maybe we could put it
somewhere too, maybe also multiple subsystems? I'm thinking something
between MM, SCHEDULER, EXEC, perhaps PIDFD?