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

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Message-Id: <20250430144236.1877ef24177b40cc6a007874@linux-foundation.org>
Date: Wed, 30 Apr 2025 14:42:36 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
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, 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.