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[134.134.136.126]) by mx.google.com with ESMTPS id p80si706729pfi.124.2019.02.07.17.44.21 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 07 Feb 2019 17:44:21 -0800 (PST) Received-SPF: pass (google.com: domain of ira.weiny@intel.com designates 134.134.136.126 as permitted sender) client-ip=134.134.136.126; Authentication-Results: mx.google.com; spf=pass (google.com: domain of ira.weiny@intel.com designates 134.134.136.126 as permitted sender) smtp.mailfrom=ira.weiny@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 07 Feb 2019 17:44:20 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,346,1544515200"; d="scan'208";a="298118289" Received: from iweiny-desk2.sc.intel.com ([10.3.52.157]) by orsmga005.jf.intel.com with ESMTP; 07 Feb 2019 17:44:20 -0800 Date: Thu, 7 Feb 2019 17:44:04 -0800 From: Ira Weiny To: Dan Williams Cc: Jason Gunthorpe , Dave Chinner , Doug Ledford , Christopher Lameter , Matthew Wilcox , Jan Kara , lsf-pc@lists.linux-foundation.org, linux-rdma , Linux MM , Linux Kernel Mailing List , John Hubbard , Jerome Glisse , Michal Hocko Subject: Re: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA Message-ID: <20190208014403.GA32701@iweiny-DESK2.sc.intel.com> References: <47820c4d696aee41225854071ec73373a273fd4a.camel@redhat.com> <01000168c43d594c-7979fcf8-b9c1-4bda-b29a-500efe001d66-000000@email.amazonses.com> <20190206210356.GZ6173@dastard> <20190206220828.GJ12227@ziepe.ca> <0c868bc615a60c44d618fb0183fcbe0c418c7c83.camel@redhat.com> <20190207035258.GD6173@dastard> <20190207052310.GA22726@ziepe.ca> <20190207171736.GD22726@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.1 (2018-12-01) 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, Feb 07, 2019 at 03:54:58PM -0800, Dan Williams wrote: > On Thu, Feb 7, 2019 at 9:17 AM Jason Gunthorpe wrote: > > > > Insisting to run RDMA & DAX without ODP and building an elaborate > > revoke mechanism to support non-ODP HW is inherently baroque. > > > > Use the HW that supports ODP. > > > > Since no HW can do disable of a MR, the escalation path is SIGKILL > > which makes it a non-production toy. > > > > What you keep missing is that for people doing this - the RDMA is a > > critical compoment of the system, you can't just say the kernel will > > randomly degrade/kill RDMA processes - that is a 'toy' configuration > > that is not production worthy. > > > > Especially since this revoke idea is basically a DOS engine for the > > RDMA protocol if another process can do actions to trigger revoke. Now > > we have a new class of security problems. (again, screams non > > production toy) > > > > The only production worthy way is to have the FS be a partner in > > making this work without requiring revoke, so the critical RDMA > > traffic can operate safely. > > > > Otherwise we need to stick to ODP. > > Thanks for this it clears a lot of things up for me... > > ...but this statement: > > > The only production worthy way is to have the FS be a partner in > > making this work without requiring revoke, so the critical RDMA > > traffic can operate safely. > > ...belies a path forward. Just swap out "FS be a partner" with "system > administrator be a partner". In other words, If the RDMA stack can't > tolerate an MR being disabled then the administrator needs to actively > disable the paths that would trigger it. Turn off reflink, don't > truncate, avoid any future FS feature that might generate unwanted > lease breaks. We would need to make sure that lease notifications > include the information to identify the lease breaker to debug escapes > that might happen, but it is a solution that can be qualified to not > lease break. In any event, this lets end users pick their filesystem > (modulo RDMA incompatible features), provides an enumeration of lease > break sources in the kernel, and opens up FS-DAX to a wider array of > RDMA adapters. In general this is what Linux has historically done, > give end users technology freedom. To back off the details of this thread a bit... The details of limitations imposed and how they would be tracked within the kernel would be a great thing to discuss face to face. Hence the reason for my proposal as a topic. Ira