From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id E169E6B0069 for ; Wed, 19 Oct 2016 04:52:07 -0400 (EDT) Received: by mail-wm0-f72.google.com with SMTP id c78so11479472wme.1 for ; Wed, 19 Oct 2016 01:52:07 -0700 (PDT) Received: from mail-wm0-f68.google.com (mail-wm0-f68.google.com. [74.125.82.68]) by mx.google.com with ESMTPS id b65si3533181wme.66.2016.10.19.01.52.06 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 19 Oct 2016 01:52:06 -0700 (PDT) Received: by mail-wm0-f68.google.com with SMTP id d199so2913401wmd.1 for ; Wed, 19 Oct 2016 01:52:06 -0700 (PDT) Date: Wed, 19 Oct 2016 10:52:05 +0200 From: Michal Hocko Subject: Re: [PATCH 08/10] mm: replace __access_remote_vm() write parameter with gup_flags Message-ID: <20161019085204.GD7517@dhcp22.suse.cz> References: <20161013002020.3062-1-lstoakes@gmail.com> <20161013002020.3062-9-lstoakes@gmail.com> <20161019075903.GP29967@quack2.suse.cz> <20161019081352.GB7562@dhcp22.suse.cz> <20161019084045.GA19441@lucifer> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161019084045.GA19441@lucifer> Sender: owner-linux-mm@kvack.org List-ID: To: Lorenzo Stoakes Cc: Jan Kara , linux-mm@kvack.org, Linus Torvalds , Hugh Dickins , Dave Hansen , Rik van Riel , Mel Gorman , Andrew Morton , adi-buildroot-devel@lists.sourceforge.net, ceph-devel@vger.kernel.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, kvm@vger.kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-cris-kernel@axis.com, linux-fbdev@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-mips@linux-mips.org, linux-rdma@vger.kernel.org, linux-s390@vger.kernel.org, linux-samsung-soc@vger.kernel.org, linux-scsi@vger.kernel.org, linux-security-module@vger.kernel.org, linux-sh@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, sparclinux@vger.kernel.org, x86@kernel.org On Wed 19-10-16 09:40:45, Lorenzo Stoakes wrote: > On Wed, Oct 19, 2016 at 10:13:52AM +0200, Michal Hocko wrote: > > On Wed 19-10-16 09:59:03, Jan Kara wrote: > > > On Thu 13-10-16 01:20:18, Lorenzo Stoakes wrote: > > > > This patch removes the write parameter from __access_remote_vm() and replaces it > > > > with a gup_flags parameter as use of this function previously _implied_ > > > > FOLL_FORCE, whereas after this patch callers explicitly pass this flag. > > > > > > > > We make this explicit as use of FOLL_FORCE can result in surprising behaviour > > > > (and hence bugs) within the mm subsystem. > > > > > > > > Signed-off-by: Lorenzo Stoakes > > > > > > So I'm not convinced this (and the following two patches) is actually > > > helping much. By grepping for FOLL_FORCE we will easily see that any caller > > > of access_remote_vm() gets that semantics and can thus continue search > > > > I am really wondering. Is there anything inherent that would require > > FOLL_FORCE for access_remote_vm? I mean FOLL_FORCE is a really > > non-trivial thing. It doesn't obey vma permissions so we should really > > minimize its usage. Do all of those users really need FOLL_FORCE? > > I wonder about this also, for example by accessing /proc/self/mem you trigger > access_remote_vm() and consequently get_user_pages_remote() meaning FOLL_FORCE > is implied and you can use /proc/self/mem to override any VMA permissions. I yes this is the desirable and expected behavior. > wonder if this is desirable behaviour or whether this ought to be limited to > ptrace system calls. Regardless, by making the flag more visible it makes it > easier to see that this is happening. mem_open already enforces PTRACE_MODE_ATTACH -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org