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Thu, 08 Apr 2021 03:05:16 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id l4sm12802446wmh.8.2021.04.08.03.05.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Apr 2021 03:05:15 -0700 (PDT) Date: Thu, 8 Apr 2021 12:05:13 +0200 From: Daniel Vetter To: Jason Gunthorpe Cc: Daniel Vetter , DRI Development , LKML , kvm@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-media@vger.kernel.org, 3pvd@google.com, Jann Horn , Paolo Bonzini , Cornelia Huck , Peter Xu , Alex Williamson , Daniel Vetter Subject: Re: [PATCH 3/3] mm: unexport follow_pfn Message-ID: Mail-Followup-To: Jason Gunthorpe , DRI Development , LKML , kvm@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-media@vger.kernel.org, 3pvd@google.com, Jann Horn , Paolo Bonzini , Cornelia Huck , Peter Xu , Alex Williamson , Daniel Vetter References: <20210316153303.3216674-1-daniel.vetter@ffwll.ch> <20210316153303.3216674-4-daniel.vetter@ffwll.ch> <20210329133101.GA1168973@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210329133101.GA1168973@nvidia.com> X-Operating-System: Linux phenom 5.7.0-1-amd64 X-Stat-Signature: 6bczeu917dhmhppn7ibdjm8ausa7ptyn X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0A2C25001535 Received-SPF: none (ffwll.ch>: No applicable sender policy available) receiver=imf01; identity=mailfrom; envelope-from=""; helo=mail-wr1-f45.google.com; client-ip=209.85.221.45 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617876316-542176 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Mar 29, 2021 at 10:31:01AM -0300, Jason Gunthorpe wrote: > On Tue, Mar 16, 2021 at 04:33:03PM +0100, Daniel Vetter wrote: > > Both kvm (in bd2fae8da794 ("KVM: do not assume PTE is writable after > > follow_pfn")) and vfio (in 07956b6269d3 ("vfio/type1: Use > > follow_pte()")) have lost their callsites of follow_pfn(). All the > > other ones have been switched over to unsafe_follow_pfn because they > > cannot be fixed without breaking userspace api. > > > > Argueably the vfio code is still racy, but that's kinda a bigger > > vfio and kvm Hm I thought kvm is non-racy due to the mmu notifier catch races? > > > picture. But since it does leak the pte beyond where it drops the pt > > lock, without anything else like an mmu notifier guaranteeing > > coherence, the problem is at least clearly visible in the vfio code. > > So good enough with me. > > > > I've decided to keep the explanation that after dropping the pt lock > > you must have an mmu notifier if you keep using the pte somehow by > > adjusting it and moving it into the kerneldoc for the new follow_pte() > > function. > > > > Cc: 3pvd@google.com > > Cc: Jann Horn > > Cc: Paolo Bonzini > > Cc: Jason Gunthorpe > > Cc: Cornelia Huck > > Cc: Peter Xu > > Cc: Alex Williamson > > Cc: linux-mm@kvack.org > > Cc: linux-arm-kernel@lists.infradead.org > > Cc: linux-samsung-soc@vger.kernel.org > > Cc: linux-media@vger.kernel.org > > Cc: kvm@vger.kernel.org > > Signed-off-by: Daniel Vetter > > --- > > include/linux/mm.h | 2 -- > > mm/memory.c | 26 +++++--------------------- > > mm/nommu.c | 13 +------------ > > 3 files changed, 6 insertions(+), 35 deletions(-) > > Reviewed-by: Jason Gunthorpe Thanks for your r-b tags, I'll add them. -Daniel > > Jason -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch