From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: Re: [PATCH v4 1/2] arm64: Define Documentation/arm64/tagged-address-abi.txt Date: Thu, 13 Jun 2019 16:39:07 +0100 Message-ID: <20190613153906.GV28951@C02TF0J2HF1T.local> References: <20190612142111.28161-1-vincenzo.frascino@arm.com> <20190612142111.28161-2-vincenzo.frascino@arm.com> <20190612153538.GL28951@C02TF0J2HF1T.local> <141c740a-94c2-2243-b6d1-b44ffee43791@arm.com> <20190613113731.GY28398@e103592.cambridge.arm.com> <20190613122821.GS28951@C02TF0J2HF1T.local> <20190613132342.GZ28398@e103592.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190613132342.GZ28398@e103592.cambridge.arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Dave Martin Cc: linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, Szabolcs Nagy , Andrey Konovalov , Will Deacon , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Alexander Viro , linux-kselftest@vger.kernel.org, Vincenzo Frascino , linux-arm-kernel@lists.infradead.org List-Id: linux-arch.vger.kernel.org On Thu, Jun 13, 2019 at 02:23:43PM +0100, Dave P Martin wrote: > On Thu, Jun 13, 2019 at 01:28:21PM +0100, Catalin Marinas wrote: > > On Thu, Jun 13, 2019 at 12:37:32PM +0100, Dave P Martin wrote: > > > On Thu, Jun 13, 2019 at 11:15:34AM +0100, Vincenzo Frascino wrote: > > > > On 12/06/2019 16:35, Catalin Marinas wrote: > > > > > On Wed, Jun 12, 2019 at 03:21:10PM +0100, Vincenzo Frascino wrote: > > > > >> + - PR_GET_TAGGED_ADDR_CTRL: can be used to check the status of the Tagged > > > > >> + Address ABI. > > [...] > > > Is there a canonical way to detect whether this whole API/ABI is > > > available? (i.e., try to call this prctl / check for an HWCAP bit, > > > etc.) > > > > The canonical way is a prctl() call. HWCAP doesn't make sense since it's > > not a hardware feature. If you really want a different way of detecting > > this (which I don't think it's worth), we can reinstate the AT_FLAGS > > bit. > > Sure, I think this probably makes sense -- I'm still getting my around > which parts of the design are directly related to MTE and which aren't. > > I was a bit concerned about the interaction between > PR_SET_TAGGED_ADDR_CTRL and the sysctl: the caller might conclude that > this API is unavailable when actually tagged addresses are stuck on. > > I'm not sure whether this matters, but it's a bit weird. > > One option would be to change the semantics, so that the sysctl just > forbids turning tagging from off to on. Alternatively, we could return > a different error code to distinguish this case. This is the intention, just to forbid turning tagging on. We could return -EPERM instead, though my original intent was to simply pretend that the prctl does not exist like in an older kernel version. -- Catalin From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.110.172]:43218 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731932AbfFMPjX (ORCPT ); Thu, 13 Jun 2019 11:39:23 -0400 Date: Thu, 13 Jun 2019 16:39:07 +0100 From: Catalin Marinas Subject: Re: [PATCH v4 1/2] arm64: Define Documentation/arm64/tagged-address-abi.txt Message-ID: <20190613153906.GV28951@C02TF0J2HF1T.local> References: <20190612142111.28161-1-vincenzo.frascino@arm.com> <20190612142111.28161-2-vincenzo.frascino@arm.com> <20190612153538.GL28951@C02TF0J2HF1T.local> <141c740a-94c2-2243-b6d1-b44ffee43791@arm.com> <20190613113731.GY28398@e103592.cambridge.arm.com> <20190613122821.GS28951@C02TF0J2HF1T.local> <20190613132342.GZ28398@e103592.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190613132342.GZ28398@e103592.cambridge.arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Dave Martin Cc: linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, Szabolcs Nagy , Andrey Konovalov , Will Deacon , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Alexander Viro , linux-kselftest@vger.kernel.org, Vincenzo Frascino , linux-arm-kernel@lists.infradead.org Message-ID: <20190613153907.z6WS26iMY3FZOqFEeC8_Ex6Rs-53dxPbXmOhCSPTG2s@z> On Thu, Jun 13, 2019 at 02:23:43PM +0100, Dave P Martin wrote: > On Thu, Jun 13, 2019 at 01:28:21PM +0100, Catalin Marinas wrote: > > On Thu, Jun 13, 2019 at 12:37:32PM +0100, Dave P Martin wrote: > > > On Thu, Jun 13, 2019 at 11:15:34AM +0100, Vincenzo Frascino wrote: > > > > On 12/06/2019 16:35, Catalin Marinas wrote: > > > > > On Wed, Jun 12, 2019 at 03:21:10PM +0100, Vincenzo Frascino wrote: > > > > >> + - PR_GET_TAGGED_ADDR_CTRL: can be used to check the status of the Tagged > > > > >> + Address ABI. > > [...] > > > Is there a canonical way to detect whether this whole API/ABI is > > > available? (i.e., try to call this prctl / check for an HWCAP bit, > > > etc.) > > > > The canonical way is a prctl() call. HWCAP doesn't make sense since it's > > not a hardware feature. If you really want a different way of detecting > > this (which I don't think it's worth), we can reinstate the AT_FLAGS > > bit. > > Sure, I think this probably makes sense -- I'm still getting my around > which parts of the design are directly related to MTE and which aren't. > > I was a bit concerned about the interaction between > PR_SET_TAGGED_ADDR_CTRL and the sysctl: the caller might conclude that > this API is unavailable when actually tagged addresses are stuck on. > > I'm not sure whether this matters, but it's a bit weird. > > One option would be to change the semantics, so that the sysctl just > forbids turning tagging from off to on. Alternatively, we could return > a different error code to distinguish this case. This is the intention, just to forbid turning tagging on. We could return -EPERM instead, though my original intent was to simply pretend that the prctl does not exist like in an older kernel version. -- Catalin