From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9516248A8CD; Fri, 25 Sep 2026 09:54:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790330067; cv=none; b=ijtGStakSdymKbRPYijD20eY7HzcMuZxLcXJsLpd2GxSqo5C4ga1MU+jaj5OP2DMLbIF9AAZeXm1VG0lvYXwRJh1UQJ9bQi7hccLNu98gBiasCbTOfLLR0EewM2TpzGSsICTrz2kiY+abdJtfRoPpyCK0qgi3RWvIfnNq7vdms4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790330067; c=relaxed/simple; bh=TmE/BY2lwmHgp/kflo2mcoio9Q11DXGCtop3HSrzs6E=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=q0cHcKM+5LnAgLO0HfEaLUZrkQVIZ1+IIE0qOTVMQKV9oQbw8lA+1CBOCKD/Qr3FTji9RdFE/WeISeDpc/0HDY3Sec5lGK+1XsfUFUZKtHr07UbX8FbucQlRwWuTMbpEpwsxSmh8JrF0oALI0klgjHoJQb5sfFF057vCZaVza5w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MsAuqFOO; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MsAuqFOO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6ABF21F00893; Fri, 25 Sep 2026 09:53:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790330064; bh=F26o3Lz6j0FulgVu/J70FouYk+xm4Aj0BzlXmkWYx74=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=MsAuqFOOx+AF1dgN+IqsXkW8tPskls72sr+6/efWMWpfVIAlZSDWLuBHTrLZClhgG q/dIOEfA2AyCRm9jA5KWXH0p9qG5z3u3QSSdut4cDfuHJ9MY2s5zp+Of3VIDKk9aQh cjBRq0th+AWyc2+NbiAThoZzNXCNSNida0MNqGcbx/Gp+nAuExhBiSODnPz+COmnw9 Q5xFbgOZ6EBRN1Z/dgGPytz/TJE4uK9b62Ug/ZoKT2bY5zp22H3YyXonIbjvgfMmsP Ity7rFv41f14MLa4FLJtZ16dM7J7DZuG6gjVmfVxCKHLOVNegP/UQM/eBy2REvzB/4 t2NDXRrsRj7PA== Date: Fri, 25 Sep 2026 10:53:53 +0100 From: "Lorenzo Stoakes (ARM)" To: Suren Baghdasaryan Cc: Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato , David Hildenbrand , Mike Rapoport , Michal Hocko , Jonathan Corbet , Greg Kroah-Hartman , Dennis Dalessandro , Jason Gunthorpe , Leon Romanovsky , Paul Moore , Stephen Smalley , Jaroslav Kysela , Takashi Iwai , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Doug Gilbert , "James E.J. Bottomley" , "Martin K. Petersen" , Jaya Kumar , Simona Vetter , Helge Deller , Sebastian Reichel , John Hubbard , Peter Xu , Masami Hiramatsu , Oleg Nesterov , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Rik van Riel , Harry Yoo , Juri Lelli , Vincent Guittot , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Arnd Bergmann , Muchun Song , Oscar Salvador , "Matthew Wilcox (Oracle)" , Jan Kara , Marc Zyngier , Oliver Upton , Catalin Marinas , Madhavan Srinivasan , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , "David S. Miller" , Andreas Larsson , Alexander Viro , Christian Brauner , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Youngjun Park , Johannes Weiner , Qi Zheng , Shakeel Butt , Axel Rasmussen , Yuanchu Xie , Wei Xu , Chengming Zhou , Michal Hocko , Miklos Szeredi , Xu Xin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-usb@vger.kernel.org, linux-rdma@vger.kernel.org, selinux@vger.kernel.org, linux-sound@vger.kernel.org, bpf@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, fuse-devel@lists.linux.dev Subject: Re: [PATCH v3 05/40] mm/vma: ensure mmap_prepare doesn't set actions on a mergeable vma Message-ID: References: <20260917-b4-mmap-prepare-vma-flag-sanify-v3-0-4583d8a23bca@kernel.org> <20260917-b4-mmap-prepare-vma-flag-sanify-v3-5-4583d8a23bca@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Fri, Sep 25, 2026 at 12:28:49AM -0700, Suren Baghdasaryan wrote: > On Thu, Sep 17, 2026 at 9:25 AM Lorenzo Stoakes (ARM) wrote: > > > > When a user requests an mmap_action be performed in mmap_prepare, this > > involves populating the VMA range with data. > > > > However, if the VMA is mergeable, it might then mistakenly be merged with > > another VMA without having populated the range. > > > > Every mmap action currently available sets VMA flags such that the VMA > > cannot be merged. > > > > However, to ensure that no future mmap action falls foul of this, assert > > that this is the case upon mmap_prepare validation. > > > > Signed-off-by: Lorenzo Stoakes (ARM) > > Reviewed-by: Suren Baghdasaryan Thanks! > > > --- > > mm/vma.c | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/mm/vma.c b/mm/vma.c > > index d6ed10cefc8f..62f2ce1ad5a1 100644 > > --- a/mm/vma.c > > +++ b/mm/vma.c > > @@ -2809,6 +2809,15 @@ static int mmap_validate(unsigned long prev_start, unsigned long prev_end, > > int mmap_prepare_validate(const struct vm_area_desc *prev_desc, > > const struct vm_area_desc *desc) > > { > > + /* > > + * It is not valid to execute mmap actions for VMAs which can be merged, > > + * as any such merge would leave portions of the mapping incorrectly > > + * unmapped. > > + */ > > + if (vma_flags_can_merge(&desc->vma_flags) && > > + WARN_ON_ONCE(desc->action.type != MMAP_NOTHING)) > > Any reason you chose this "if (A && WARN_ON_ONCE(B))" pattern instead > of a simpler "if (WARN_ON_ONCE(A && B))"? Unless there are races > between A and B updates, I think these would be equivalent, right? They are equivalent yes! So it's more of a style thing, as that reads less clearly to me: if (WARN_ON_ONCE(vma_flags_can_merge(&desc->vma_flags) && desc->action.type != MMAP_NOTHING)) And this version highlights what is the broken thing here (action type set) a little more clearly though obviously that's only if mergeable so arguable. I don't have a really strong opinion though I can change it if you prefer? > > > + return -EINVAL; > > + > > return mmap_validate(prev_desc->start, prev_desc->end, > > desc->start, desc->end, > > &prev_desc->vma_flags, &desc->vma_flags); > > > > -- > > 2.55.0 > > -- Cheers, Lorenzo