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[209.85.220.65]) by mx.google.com with SMTPS id i5sor2665139oto.178.2019.05.16.06.14.35 for (Google Transport Security); Thu, 16 May 2019 06:14:35 -0700 (PDT) Received-SPF: pass (google.com: domain of jannh@google.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=fReDa0z9; spf=pass (google.com: domain of jannh@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=jannh@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ROaA0wXtesoRLV9jmYQxe8dOtv7TkiCY5hrIvCy7dF4=; b=fReDa0z9uHf+JdOnFb05L1Sb2NczVkeE/wfdtsKJtVRJdlu/Fy7TPQQlZVllJGEfVI RGg7FWvRbo8E6AVP8MLFTeXB72jglZuZienY2l/zowEbQoOpIBaa/+jFnlle3GzGFc3X xNigM0FnR9XrDOEY5QID9N8l7rr1SPmrT5PfodS5GKNfnFOfOth2NQIDjT3rgcY+M3vB Cfuq7MjGvfW0ty3Bhj2YvrKqrFz97mPOyFCFMPTS0hiLi4mZ+3MOlRoB3Jehl3WmsUD2 iBrqKjQNY+qEgbDG40juKK/o/hmnoDNXWF12m1KsESJx4v2wbFNzxs5C0nwXyl5NB/mP /Q/Q== X-Google-Smtp-Source: APXvYqz8ONif2CczL0twdpVOaBW6vNrGkKqpu7xEjjDuQ4L9r3lh6OrdS3yiomN/QUeXmHuUGmjDQ0jYNaDLm4icWVQ= X-Received: by 2002:a9d:6954:: with SMTP id p20mr8910155oto.337.1558012474998; Thu, 16 May 2019 06:14:34 -0700 (PDT) MIME-Version: 1.0 References: <155793276388.13922.18064660723547377633.stgit@localhost.localdomain> <456c7367-0656-933b-986d-febdcc5ab98e@virtuozzo.com> In-Reply-To: <456c7367-0656-933b-986d-febdcc5ab98e@virtuozzo.com> From: Jann Horn Date: Thu, 16 May 2019 15:14:08 +0200 Message-ID: Subject: Re: [PATCH RFC 0/5] mm: process_vm_mmap() -- syscall for duplication a process mapping To: Kirill Tkhai Cc: Andrew Morton , Dan Williams , Michal Hocko , keith.busch@intel.com, "Kirill A . Shutemov" , pasha.tatashin@oracle.com, Alexander Duyck , ira.weiny@intel.com, Andrey Konovalov , arunks@codeaurora.org, Vlastimil Babka , Christoph Lameter , Rik van Riel , Kees Cook , hannes@cmpxchg.org, npiggin@gmail.com, Mathieu Desnoyers , Shakeel Butt , Roman Gushchin , Andrea Arcangeli , Hugh Dickins , Jerome Glisse , Mel Gorman , daniel.m.jordan@oracle.com, kernel list , Linux-MM 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, May 16, 2019 at 3:03 PM Kirill Tkhai wrote: > On 15.05.2019 21:46, Jann Horn wrote: > > On Wed, May 15, 2019 at 5:11 PM Kirill Tkhai wrote: > >> This patchset adds a new syscall, which makes possible > >> to clone a mapping from a process to another process. > >> The syscall supplements the functionality provided > >> by process_vm_writev() and process_vm_readv() syscalls, > >> and it may be useful in many situation. > >> > >> For example, it allows to make a zero copy of data, > >> when process_vm_writev() was previously used: > > [...] > >> This syscall may be used for page servers like in example > >> above, for migration (I assume, even virtual machines may > >> want something like this), for zero-copy desiring users > >> of process_vm_writev() and process_vm_readv(), for debug > >> purposes, etc. It requires the same permittions like > >> existing proc_vm_xxx() syscalls have. > > > > Have you considered using userfaultfd instead? userfaultfd has > > interfaces (UFFDIO_COPY and UFFDIO_ZERO) for directly shoving pages > > into the VMAs of other processes. This works without the churn of > > creating and merging VMAs all the time. userfaultfd is the interface > > that was written to support virtual machine migration (and it supports > > live migration, too). > > I know about userfaultfd, but it does solve the discussed problem. > It allocates new pages to make UFFDIO_COPY (see mcopy_atomic_pte()), > and it accumulates all the disadvantages, the example from [0/5] > message has. Sorry, right, I misremembered that.