From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5A39FC433DB for ; Fri, 12 Feb 2021 14:45:22 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 105EE64E79 for ; Fri, 12 Feb 2021 14:45:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 105EE64E79 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=ercH4x95kftlrnS3KX9+yiMUYE+Hu63p3aAbPCOgF8o=; b=0P65mA7tPJRRHJHiY8Rg+vdwS v1csGCIXrGwS0JNbzNxe88uRpTUvRicrtXDQW16cItbN8OXQQZ0v+LhrEa+dxYFIaRrbiV88XjE/q 2AQkkwiOBDdSoNyj40mHVXTEbejMUWvd86+j8BsVYjR/Jt4khz6wrOigMHI1MzusT1gUCGLlaAql+ GI9/zYcDf7is3pasQ6VdavCyqiuohCJag1uTRBTQX1esoJxoCbFLNqVxtYwDBUxMFCOcLGMnItHue am5CdOiSjwcbLt7fBJVdgnle1MfRW842kSncXE9GZjNL4S/LQrf5F2LzwE0XqvxMAvLcLMC5mHNWU 9v/R2wBaw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1lAZg5-0005iP-7U; Fri, 12 Feb 2021 14:44:13 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1lAZg1-0005he-UZ for linux-arm-kernel@lists.infradead.org; Fri, 12 Feb 2021 14:44:11 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 40F2E64DAD; Fri, 12 Feb 2021 14:44:04 +0000 (UTC) Date: Fri, 12 Feb 2021 14:44:01 +0000 From: Catalin Marinas To: David Laight Subject: Re: [RESEND RFC PATCH v2] arm64: Exposes support for 32-bit syscalls Message-ID: <20210212144400.GD7718@arm.com> References: <20210211202208.31555-1-Sonicadvance1@gmail.com> <58b03e17-3729-99ea-8691-0d735a53b9bc@arm.com> <20210212123515.GC6057@sirena.org.uk> <20210212132807.GC7718@arm.com> <7300c3cbce95498b9fbe7ee754250794@AcuMS.aculab.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <7300c3cbce95498b9fbe7ee754250794@AcuMS.aculab.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210212_094410_129272_BE55A429 X-CRM114-Status: GOOD ( 34.05 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Gavin Shan , "linux-kernel@vger.kernel.org" , Julien Grall , Amit Daniel Kachhap , Vincenzo Frascino , Will Deacon , Qais Yousef , Jean-Philippe Brucker , Marc Zyngier , Anshuman Khandual , Andrey Ignatov , Steven Price , Sami Tolvanen , David Brazdil , Dave Martin , Kees Cook , "sonicadvance1@gmail.com" , Frederic Weisbecker , Kristina Martsenko , Mark Brown , Al Viro , Kevin Hao , Peter Collingbourne , "linux-arm-kernel@lists.infradead.org" , Jens Axboe , "amanieu@gmail.com" , Jason Yan , Oleg Nesterov , Tian Tao , Andrew Morton , Mike Rapoport Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Feb 12, 2021 at 02:12:02PM +0000, David Laight wrote: > From: Catalin Marinas > > Sent: 12 February 2021 13:28 > > On Fri, Feb 12, 2021 at 12:35:15PM +0000, Mark Brown wrote: > > > On Fri, Feb 12, 2021 at 11:30:41AM +0000, Steven Price wrote: > > > > On 11/02/2021 20:21, sonicadvance1@gmail.com wrote: > > > > > Why do we need compatibility layers? > > > > > There are ARMv8 CPUs that only support AArch64 but still need to run > > > > > AArch32 applications. > > > > > Cortex-A34/R82 and other cores are prime examples of this. > > > > > Additionally if a user is needing to run legacy 32-bit x86 software, it > > > > > needs the same compatibility layer. > > > > > > > Unless I'm much mistaken QEMU's user mode already does this - admittedly I > > > > don't tend to run "legacy 32-bit x86 software". > > > > > > Yes, this has been deployed on Debian for a long time - you can install > > > any combination of Debian architectures on a single system and it will > > > use qemu to run binaries that can't be supported natively by the > > > hardware. > > > > The only downside I think is that for some syscalls it's not that > > efficient. Those using struct iovec come to mind, qemu probably > > duplicates the user structures, having to copy them in both directions > > (well, the kernel compat layer does something similar). > > > > Anyway, I'm not in favour of this patch. Those binary translation tools > > need to explore the user-only options first and come up with some perf > > numbers to justify the proposal. > > I don't think the problem is only the performance. > The difficulty is knowing when structures need changing. > A typical example is driver ioctl requests. The ioctl is indeed the difficult case not necessarily because of changing structures but rather their large amount. For the generic syscalls, the existing ABI is very rarely changed. It is, however, evolving (new syscalls) and such binary translation tool would need to keep up or at least intercept syscalls like uname and report older kernel versions. > Any user space adaption layer would have to know which actual > driver has been opened and what internal structures it has. > Getting that right is hard and difficult. > The recent changes to move (IIRC) sockopt compatibility down > into the protocol code found quite a few places where it was > previously broken. > It is much easier to get it right in the code that knows about > the actual structures. As Arnd I think was suggesting, we could have an ioctl32() syscall that allows compat arguments but not opening up the whole set of compat syscalls to native processes. > For mmap() you certainly want to be able to limit the returned > address to 32 bits (or maybe 31.5 bits). > A MAP_BELOW flag could do that, but the 32bit syscall has to. > (I can't remember what is done for wine - which needs 31bit addresses). For mmap(), we can easily add support for PER_LINUX_32BIT or PER_LINUX32_3GB, so we don't need to change the mmap() parameters. I don't recall to have had a (strong) request for this. > Of course, that only helps for 32bit arm binaries - when the kernel > compat code is written for, Trying to run x86 binaries adds extra > complexity. Indeed. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 48DA0C433E0 for ; Fri, 12 Feb 2021 14:44:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1A0A264E6B for ; Fri, 12 Feb 2021 14:44:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230047AbhBLOow (ORCPT ); Fri, 12 Feb 2021 09:44:52 -0500 Received: from mail.kernel.org ([198.145.29.99]:48466 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229517AbhBLOou (ORCPT ); Fri, 12 Feb 2021 09:44:50 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 40F2E64DAD; Fri, 12 Feb 2021 14:44:04 +0000 (UTC) Date: Fri, 12 Feb 2021 14:44:01 +0000 From: Catalin Marinas To: David Laight Cc: Mark Brown , Steven Price , "sonicadvance1@gmail.com" , "amanieu@gmail.com" , Will Deacon , Mark Rutland , Oleg Nesterov , Al Viro , Dave Martin , Amit Daniel Kachhap , Marc Zyngier , David Brazdil , Jean-Philippe Brucker , Andrew Morton , Anshuman Khandual , Gavin Shan , Mike Rapoport , Vincenzo Frascino , Kristina Martsenko , Kees Cook , Sami Tolvanen , Frederic Weisbecker , Kevin Hao , Jason Yan , Andrey Ignatov , Peter Collingbourne , Julien Grall , Tian Tao , Qais Yousef , Jens Axboe , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [RESEND RFC PATCH v2] arm64: Exposes support for 32-bit syscalls Message-ID: <20210212144400.GD7718@arm.com> References: <20210211202208.31555-1-Sonicadvance1@gmail.com> <58b03e17-3729-99ea-8691-0d735a53b9bc@arm.com> <20210212123515.GC6057@sirena.org.uk> <20210212132807.GC7718@arm.com> <7300c3cbce95498b9fbe7ee754250794@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7300c3cbce95498b9fbe7ee754250794@AcuMS.aculab.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 12, 2021 at 02:12:02PM +0000, David Laight wrote: > From: Catalin Marinas > > Sent: 12 February 2021 13:28 > > On Fri, Feb 12, 2021 at 12:35:15PM +0000, Mark Brown wrote: > > > On Fri, Feb 12, 2021 at 11:30:41AM +0000, Steven Price wrote: > > > > On 11/02/2021 20:21, sonicadvance1@gmail.com wrote: > > > > > Why do we need compatibility layers? > > > > > There are ARMv8 CPUs that only support AArch64 but still need to run > > > > > AArch32 applications. > > > > > Cortex-A34/R82 and other cores are prime examples of this. > > > > > Additionally if a user is needing to run legacy 32-bit x86 software, it > > > > > needs the same compatibility layer. > > > > > > > Unless I'm much mistaken QEMU's user mode already does this - admittedly I > > > > don't tend to run "legacy 32-bit x86 software". > > > > > > Yes, this has been deployed on Debian for a long time - you can install > > > any combination of Debian architectures on a single system and it will > > > use qemu to run binaries that can't be supported natively by the > > > hardware. > > > > The only downside I think is that for some syscalls it's not that > > efficient. Those using struct iovec come to mind, qemu probably > > duplicates the user structures, having to copy them in both directions > > (well, the kernel compat layer does something similar). > > > > Anyway, I'm not in favour of this patch. Those binary translation tools > > need to explore the user-only options first and come up with some perf > > numbers to justify the proposal. > > I don't think the problem is only the performance. > The difficulty is knowing when structures need changing. > A typical example is driver ioctl requests. The ioctl is indeed the difficult case not necessarily because of changing structures but rather their large amount. For the generic syscalls, the existing ABI is very rarely changed. It is, however, evolving (new syscalls) and such binary translation tool would need to keep up or at least intercept syscalls like uname and report older kernel versions. > Any user space adaption layer would have to know which actual > driver has been opened and what internal structures it has. > Getting that right is hard and difficult. > The recent changes to move (IIRC) sockopt compatibility down > into the protocol code found quite a few places where it was > previously broken. > It is much easier to get it right in the code that knows about > the actual structures. As Arnd I think was suggesting, we could have an ioctl32() syscall that allows compat arguments but not opening up the whole set of compat syscalls to native processes. > For mmap() you certainly want to be able to limit the returned > address to 32 bits (or maybe 31.5 bits). > A MAP_BELOW flag could do that, but the 32bit syscall has to. > (I can't remember what is done for wine - which needs 31bit addresses). For mmap(), we can easily add support for PER_LINUX_32BIT or PER_LINUX32_3GB, so we don't need to change the mmap() parameters. I don't recall to have had a (strong) request for this. > Of course, that only helps for 32bit arm binaries - when the kernel > compat code is written for, Trying to run x86 binaries adds extra > complexity. Indeed. -- Catalin