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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 56081C433E6 for ; Fri, 12 Feb 2021 14:14:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 25FE56023B for ; Fri, 12 Feb 2021 14:14:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231947AbhBLOOb convert rfc822-to-8bit (ORCPT ); Fri, 12 Feb 2021 09:14:31 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:23048 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231710AbhBLONs (ORCPT ); Fri, 12 Feb 2021 09:13:48 -0500 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-228-7juo4BU-O2-FOsFv4E1WeQ-1; Fri, 12 Feb 2021 14:12:05 +0000 X-MC-Unique: 7juo4BU-O2-FOsFv4E1WeQ-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 12 Feb 2021 14:12:02 +0000 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Fri, 12 Feb 2021 14:12:02 +0000 From: David Laight To: 'Catalin Marinas' , Mark Brown CC: 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 Thread-Topic: [RESEND RFC PATCH v2] arm64: Exposes support for 32-bit syscalls Thread-Index: AQHXAUNInwWNlJur40qqyYPDj4lGvapUi6pA Date: Fri, 12 Feb 2021 14:12:02 +0000 Message-ID: <7300c3cbce95498b9fbe7ee754250794@AcuMS.aculab.com> References: <20210211202208.31555-1-Sonicadvance1@gmail.com> <58b03e17-3729-99ea-8691-0d735a53b9bc@arm.com> <20210212123515.GC6057@sirena.org.uk> <20210212132807.GC7718@arm.com> In-Reply-To: <20210212132807.GC7718@arm.com> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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. 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). 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. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) 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=-4.3 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 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 C1465C433E6 for ; Fri, 12 Feb 2021 14:13:30 +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 8299364E79 for ; Fri, 12 Feb 2021 14:13:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8299364E79 Authentication-Results: mail.kernel.org; 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Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1lAZBB-0001zc-7i; Fri, 12 Feb 2021 14:12:17 +0000 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1lAZB4-0001y4-Pa for linux-arm-kernel@lists.infradead.org; Fri, 12 Feb 2021 14:12:12 +0000 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-228-7juo4BU-O2-FOsFv4E1WeQ-1; Fri, 12 Feb 2021 14:12:05 +0000 X-MC-Unique: 7juo4BU-O2-FOsFv4E1WeQ-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 12 Feb 2021 14:12:02 +0000 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Fri, 12 Feb 2021 14:12:02 +0000 From: David Laight To: 'Catalin Marinas' , Mark Brown Subject: RE: [RESEND RFC PATCH v2] arm64: Exposes support for 32-bit syscalls Thread-Topic: [RESEND RFC PATCH v2] arm64: Exposes support for 32-bit syscalls Thread-Index: AQHXAUNInwWNlJur40qqyYPDj4lGvapUi6pA Date: Fri, 12 Feb 2021 14:12:02 +0000 Message-ID: <7300c3cbce95498b9fbe7ee754250794@AcuMS.aculab.com> References: <20210211202208.31555-1-Sonicadvance1@gmail.com> <58b03e17-3729-99ea-8691-0d735a53b9bc@arm.com> <20210212123515.GC6057@sirena.org.uk> <20210212132807.GC7718@arm.com> In-Reply-To: <20210212132807.GC7718@arm.com> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; 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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 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. 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. 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). 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. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel