From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: Re: [PATCH v19 02/15] arm64: Introduce prctl() options to control the tagged user addresses ABI Date: Fri, 2 Aug 2019 11:50:38 +0100 Message-ID: <20190802105038.GC4175@arrakis.emea.arm.com> References: <1c05651c53f90d07e98ee4973c2786ccf315db12.1563904656.git.andreyknvl@google.com> <7a34470c-73f0-26ac-e63d-161191d4b1e4@intel.com> <2b274c6f-6023-8eb8-5a86-507e6000e13d@arm.com> <88c59d1e-eda9-fcfe-5ee3-64a331f34313@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <88c59d1e-eda9-fcfe-5ee3-64a331f34313@intel.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Dave Hansen Cc: Mark Rutland , kvm@vger.kernel.org, Szabolcs Nagy , Will Deacon , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, Khalid Aziz , linux-kselftest@vger.kernel.org, Felix Kuehling , Vincenzo Frascino , Jacob Bramley , Leon Romanovsky , linux-rdma@vger.kernel.org, amd-gfx@lists.freedesktop.org, Christoph Hellwig , Jason Gunthorpe , Dmitry Vyukov , Ramana Radhakrishnan , Dave Martin , Evgeniy Stepanov , linux-media@vger.kernel.org, Kees Cook , Ruben Ayrapetyan , Andrey Konovalov , Kevin Brodsky List-Id: dri-devel@lists.freedesktop.org On Thu, Aug 01, 2019 at 09:45:05AM -0700, Dave Hansen wrote: > On 8/1/19 5:38 AM, Kevin Brodsky wrote: > > This patch series only changes what is allowed or not at the syscall > > interface. It does not change the address space size. On arm64, TBI (Top > > Byte Ignore) has always been enabled for userspace, so it has never been > > possible to use the upper 8 bits of user pointers for addressing. > > Oh, so does the address space that's available already chop that out? Yes. Currently the hardware only supports 52-bit virtual addresses. It could be expanded (though it needs a 5th page table level) to 56-bit VA but it's not currently on our (hardware) plans. Beyond 56-bit, it cannot be done without breaking the software expectations (and hopefully I'll retire before we need this ;)). > > If other architectures were to support a similar functionality, then I > > agree that a common and more generic interface (if needed) would be > > helpful, but as it stands this is an arm64-specific prctl, and on arm64 > > the address tag is defined by the architecture as bits [63:56]. > > It should then be an arch_prctl(), no? I guess you just want renaming SET_TAGGED_ADDR_CTRL() to arch_prctl_tagged_addr_ctrl_set()? (similarly for 'get') -- Catalin