From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 555493F0746 for ; Tue, 10 Mar 2026 08:25:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773131125; cv=none; b=clVwTkS8+qAqpu/bKuvrQ/dANa/yTrY+tgqUNlxjvypRmnFHi/FbFvcXY1bJl3m0H1yJmjkmwlli8S2Oncs7gbBoY0d7/2nW20MsctdA1J8B0+SU14GeeTDRpY7tBxAMokz9MYJbrDkh1/qkOBbRNamM3fZ0TqKAkh3MC6lC9EA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773131125; c=relaxed/simple; bh=3mkGCn1+SE6g3BjC4GosyHZuWAmHGngGuk1f3nEWOZ0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=hRq72pQacqfvmO2YhW7LIxSTo76IwRqxcjgpP1PFRrANsTFHJbu6/D3jXWXFlXhD+O1ty8gBM+CCRZg6SDlx2GHugWQitm2ObQ7KpXGizNzOABUqSBxZG0jj14YPt2c0u8OQLwNzQQv6WRi5bsWW1pE4zIWomplLJSVS+eIdg2k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=r32POjOe; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="r32POjOe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4D579C19423; Tue, 10 Mar 2026 08:25:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773131124; bh=3mkGCn1+SE6g3BjC4GosyHZuWAmHGngGuk1f3nEWOZ0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=r32POjOe0rj5ODQJl17XFaTxfn1KO5JF0+dr/nQ2Tts2YH6vMre+CwtuFtH9oLRly txV0zmknTNme8X1zFgHE5PI8KxGEUm7MF+f/hUgyQY4lZRPeaYduZYjhGrAhoK4UMJ c/sby567r6k8FCJUZ39iOUgKz025M/doaL3azCvfxB2zfn5wX//lTfzns+wItUMmPe 8/mTfv0nKphrYrvkB8NQHEA4HrS+/ppFbhIbUY4CDL8X9zn0lZknEQHQ+vECXKdv3o tDhLowMijFdMDdw2ZIw/QiX2hAyHw5EOvnLO1BWMZIER8TazRL/2mztEtxkDjrL+7W JRFLa/BMc5TdQ== Message-ID: <4becce7a-af3e-4f29-a233-71d90f653daa@kernel.org> Date: Tue, 10 Mar 2026 09:25:17 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: prevent droppable mappings from being locked To: anthony.yznaga@oracle.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jannh@google.com, pfalcato@suse.de, Jason@zx2c4.com References: <20260306204550.8405-1-anthony.yznaga@oracle.com> <7c1db5ef-2457-46ff-ab20-dd4090570fb6@kernel.org> <7c4a45c3-298a-4a72-b551-ec687898b4f3@oracle.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 3/10/26 03:04, anthony.yznaga@oracle.com wrote: > > On 3/9/26 7:15 AM, David Hildenbrand (Arm) wrote: >> On 3/6/26 21:45, Anthony Yznaga wrote: >>> Mappings created with MAP_DROPPABLE cannot be locked via mlock() due >>> to the check in mlock_fixup(). However, they will be locked indirectly >>> if they are created after mlockall(MCL_FUTURE). >>> >>> Fixes: 9651fcedf7b9 ("mm: add MAP_DROPPABLE for designating always >>> lazily freeable mappings") >>> Signed-off-by: Anthony Yznaga >>> --- >>>   include/linux/mm.h | 3 +++ >>>   mm/mlock.c         | 4 ++-- >>>   mm/vma.c           | 2 +- >>>   3 files changed, 6 insertions(+), 3 deletions(-) >>> >>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>> index 5be3d8a8f806..bb830574d112 100644 >>> --- a/include/linux/mm.h >>> +++ b/include/linux/mm.h >>> @@ -574,6 +574,9 @@ enum { >>>   /* This mask represents all the VMA flag bits used by mlock */ >>>   #define VM_LOCKED_MASK    (VM_LOCKED | VM_LOCKONFAULT) >>>   +/* This mask prevents VMAs from being mlock'd */ >>> +#define VM_NO_MLOCK_MASK    (VM_SPECIAL | VM_DROPPABLE) >> Instead of adding that, could we cleanup further by doing something >> like the following? >> >> The usage of "vma->vm_mm" must be double checked, > > This sent me down an interesting rabbit hole since gate_vma->vm_mm is > initialized to NULL. I can't see how the gate VMA could ever be passed > to mlock_fixup() or __mmap_complete() if it's not part of the VMA tree > of an mm and is not mapped through mmap. Right, gate_vma() would be shared across all processes. Wouldn't code like the following be questionable as well? fs/coredump.c: if (vma == get_gate_vma(vma->vm_mm)) mm/vmscan.c: if (vma == get_gate_vma(vma->vm_mm)) I mean, that cannot possibly be true unless I am missing something. There are a couple of other > places in the kernel that assume the gate VMA may be encountered when > iterating VMAs, too. Am I missing something? Happy to clean these up if > it makes sense. Yes, please look into that. As an alternative, we could maybe pass current->mm to get_gate_vma() ... but it'd be best to just clean that up. -- Cheers, David