linux-kernel - Re: [PATCH v3 4/4] mm: perform VMA allocation, freeing, duplication in mm

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Message-ID: <bd42b6fd-77b9-43cd-8e30-b6d38d5e39e3@lucifer.local>
Date: Thu, 1 May 2025 11:38:16 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Vlastimil Babka <vbabka@...e.cz>,
        "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 4/4] mm: perform VMA allocation, freeing, duplication
 in mm

On Wed, Apr 30, 2025 at 02:42:36PM -0700, Andrew Morton wrote:
> On Wed, 30 Apr 2025 10:20:10 +0100 Lorenzo Stoakes <lorenzo.stoakes@...cle.com> wrote:
>
> > On Tue, Apr 29, 2025 at 09:22:59AM +0200, Vlastimil Babka wrote:
> > > On 4/28/25 17:28, Lorenzo Stoakes wrote:
> > > > Right now these are performed in kernel/fork.c which is odd and a violation
> > > > of separation of concerns, as well as preventing us from integrating this
> > > > and related logic into userland VMA testing going forward, and perhaps more
> > > > importantly - enabling us to, in a subsequent commit, make VMA
> > > > allocation/freeing a purely internal mm operation.
> > >
> > > I wonder if the last part is from an earlier version and now obsolete
> > > because there's not subsequent commit in this series and the placement of
> > > alloc/freeing in vma_init.c seems making those purely internal mm operations
> > > already? Or do you mean some further plans?
> > >
> >
> > Sorry, missed this!
> >
> > Andrew - could we delete the last part of this sentence so it reads:
> >
> > Right now these are performed in kernel/fork.c which is odd and a violation
> > of separation of concerns, as well as preventing us from integrating this
> > and related logic into userland VMA testing going forward.
>
> Sure.  The result:
>
> : Right now these are performed in kernel/fork.c which is odd and a
> : violation of separation of concerns, as well as preventing us from
> : integrating this and related logic into userland VMA testing going
> : forward.
> :
> : There is a fly in the ointment - nommu - mmap.c is not compiled if
> : CONFIG_MMU not set, and neither is vma.c.
> :
> : To square the circle, let's add a new file - vma_init.c.  This will be
> : compiled for both CONFIG_MMU and nommu builds, and will also form part of
> : the VMA userland testing.
> :
> : This allows us to de-duplicate code, while maintaining separation of
> : concerns and the ability for us to userland test this logic.
> :
> : Update the VMA userland tests accordingly, additionally adding a
> : detach_free_vma() helper function to correctly detach VMAs before freeing
> : them in test code, as this change was triggering the assert for this.
>

Perfect, thanks!