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

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Message-ID: <c1acc2a7-5950-4c56-8429-6dc1c918e367@suse.cz>
Date: Tue, 29 Apr 2025 09:22:59 +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 4/4] mm: perform VMA allocation, freeing, duplication
 in mm

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?

> 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.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>