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[209.85.167.54]) by smtp.gmail.com with ESMTPSA id j2sm1460408lfe.213.2021.01.07.14.27.05 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 Jan 2021 14:27:05 -0800 (PST) Received: by mail-lf1-f54.google.com with SMTP id l11so18459180lfg.0 for ; Thu, 07 Jan 2021 14:27:05 -0800 (PST) X-Received: by 2002:ac2:4987:: with SMTP id f7mr329288lfl.41.1610058043577; Thu, 07 Jan 2021 14:20:43 -0800 (PST) MIME-Version: 1.0 References: <20210107200402.31095-1-aarcange@redhat.com> <20210107200402.31095-3-aarcange@redhat.com> <4100a6f5-ab0b-f7e5-962f-ea1dbcb1e47e@nvidia.com> <394e17bc-8bed-4d17-5dba-9ab8052c8bea@nvidia.com> In-Reply-To: <394e17bc-8bed-4d17-5dba-9ab8052c8bea@nvidia.com> From: Linus Torvalds Date: Thu, 7 Jan 2021 14:20:27 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 2/2] mm: soft_dirty: userfaultfd: introduce wrprotect_tlb_flush_pending To: John Hubbard Cc: Andrea Arcangeli , Linux-MM , Linux Kernel Mailing List , Yu Zhao , Andy Lutomirski , Peter Xu , Pavel Emelyanov , Mike Kravetz , Mike Rapoport , Minchan Kim , Will Deacon , Peter Zijlstra , Hugh Dickins , "Kirill A. Shutemov" , Matthew Wilcox , Oleg Nesterov , Jann Horn , Kees Cook , Leon Romanovsky , Jason Gunthorpe , Jan Kara , Kirill Tkhai Content-Type: text/plain; charset="UTF-8" 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 Thu, Jan 7, 2021 at 2:14 PM John Hubbard wrote: > > > > Literally just adding a " && page_mapcount(page) == 1" in there > > (probably best done inside page_maybe_dma_pinned() itself) > > Well, that means that pages that are used for pinned DMA like this, can > not be shared with other processes. Is that an acceptable limitation > for the RDMA users? It seems a bit constraining, at first glance anyway. Hmm, add a check for the page being PageAnon(), perhaps? If it's a shared vma, then the page can be pinned shared with multiple mappings, I agree. So yeah, I didn't think it through entirely.. And maybe I'm still missing something else.. Linus