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[134.134.136.20]) by mx.google.com with ESMTPS id u19si7216610pgf.531.2019.07.31.10.05.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 31 Jul 2019 10:05:16 -0700 (PDT) Received-SPF: pass (google.com: domain of dave.hansen@intel.com designates 134.134.136.20 as permitted sender) client-ip=134.134.136.20; Authentication-Results: mx.google.com; spf=pass (google.com: domain of dave.hansen@intel.com designates 134.134.136.20 as permitted sender) smtp.mailfrom=dave.hansen@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 31 Jul 2019 10:05:15 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,330,1559545200"; d="scan'208";a="183757949" Received: from ray.jf.intel.com (HELO [10.7.201.140]) ([10.7.201.140]) by orsmga002.jf.intel.com with ESMTP; 31 Jul 2019 10:05:15 -0700 Subject: Re: [PATCH v19 02/15] arm64: Introduce prctl() options to control the tagged user addresses ABI To: Andrey Konovalov , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: Catalin Marinas , Vincenzo Frascino , Will Deacon , Mark Rutland , Andrew Morton , Greg Kroah-Hartman , Kees Cook , Yishai Hadas , Felix Kuehling , Alexander Deucher , Christian Koenig , Mauro Carvalho Chehab , Jens Wiklander , Alex Williamson , Leon Romanovsky , Luc Van Oostenryck , Dave Martin , Khalid Aziz , enh , Jason Gunthorpe , Christoph Hellwig , Dmitry Vyukov , Kostya Serebryany , Evgeniy Stepanov , Lee Smith , Ramana Radhakrishnan , Jacob Bramley , Ruben Ayrapetyan , Robin Murphy , Kevin Brodsky , Szabolcs Nagy References: <1c05651c53f90d07e98ee4973c2786ccf315db12.1563904656.git.andreyknvl@google.com> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <1c05651c53f90d07e98ee4973c2786ccf315db12.1563904656.git.andreyknvl@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit 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 7/23/19 10:58 AM, Andrey Konovalov wrote: > +long set_tagged_addr_ctrl(unsigned long arg) > +{ > + if (!tagged_addr_prctl_allowed) > + return -EINVAL; > + if (is_compat_task()) > + return -EINVAL; > + if (arg & ~PR_TAGGED_ADDR_ENABLE) > + return -EINVAL; > + > + update_thread_flag(TIF_TAGGED_ADDR, arg & PR_TAGGED_ADDR_ENABLE); > + > + return 0; > +} Instead of a plain enable/disable, a more flexible ABI would be to have the tag mask be passed in. That way, an implementation that has a flexible tag size can select it. It also ensures that userspace actually knows what the tag size is and isn't surprised if a hardware implementation changes the tag size or position. Also, this whole set deals with tagging/untagging, but there's an effective loss of address space when you do this. Is that dealt with anywhere? How do we ensure that allocations don't get placed at a tagged address before this gets turned on? Where's that checking?