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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 DE790C48BCF for ; Wed, 9 Jun 2021 16:13:37 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 8F6C5610A2 for ; Wed, 9 Jun 2021 16:13:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8F6C5610A2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ilande.co.uk Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:35264 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lr0pk-0002VW-PL for qemu-devel@archiver.kernel.org; Wed, 09 Jun 2021 12:13:36 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:33108) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lr0lZ-0005pU-4V for qemu-devel@nongnu.org; Wed, 09 Jun 2021 12:09:18 -0400 Received: from mail.ilande.co.uk ([2001:41c9:1:41f::167]:35680 helo=mail.default.ilande.bv.iomart.io) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lr0lV-0003Qb-Q4 for qemu-devel@nongnu.org; Wed, 09 Jun 2021 12:09:16 -0400 Received: from host109-155-147-70.range109-155.btcentralplus.com ([109.155.147.70] helo=[192.168.1.65]) by mail.default.ilande.bv.iomart.io with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1lr0lF-0007LO-D0; Wed, 09 Jun 2021 17:09:01 +0100 To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org References: <20210609141010.1066750-1-f4bug@amsat.org> From: Mark Cave-Ayland Message-ID: Date: Wed, 9 Jun 2021 17:09:04 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210609141010.1066750-1-f4bug@amsat.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-SA-Exim-Connect-IP: 109.155.147.70 X-SA-Exim-Mail-From: mark.cave-ayland@ilande.co.uk Subject: Re: [RFC PATCH v2 0/2] cputlb: implement load_helper_unaligned() for unaligned loads X-SA-Exim-Version: 4.2.1 (built Wed, 08 May 2019 21:11:16 +0000) X-SA-Exim-Scanned: Yes (on mail.default.ilande.bv.iomart.io) Received-SPF: pass client-ip=2001:41c9:1:41f::167; envelope-from=mark.cave-ayland@ilande.co.uk; helo=mail.default.ilande.bv.iomart.io X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, NICE_REPLY_A=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: =?UTF-8?Q?Alex_Benn=c3=a9e?= , Peter Maydell , incoming+qemu-project-qemu-11167699-3xhw7c0pviow7og92yv73e0tr-issue-360@incoming.gitlab.com, Richard Henderson , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 09/06/2021 15:10, Philippe Mathieu-Daudé wrote: (Added gitlab issue email) > Reposting Mark's patch: > https://www.mail-archive.com/qemu-devel@nongnu.org/msg814227.html > but split in 2 patches for easier review. > > Mark Cave-Ayland (1): > cputlb: implement load_helper_unaligned() for unaligned loads > > Philippe Mathieu-Daudé (1): > accel/tcg/cputlb: Extract load_helper_unaligned() from load_helper() > > accel/tcg/cputlb.c | 106 ++++++++++++++++++++++++++++++++++++--------- > 1 file changed, 85 insertions(+), 21 deletions(-) Thanks Phil. I'm replying to this to keep track of a few thoughts that came up in our discussion on IRC: - Should these unaligned accesses be handled by the memory API? - There is an overlap with Andrew Jeffrey's unaligned access patchset for the memory API at http://patchwork.ozlabs.org/project/qemu-devel/patch/20170630030058.28943-1-andrew@aj.id.au/. This would certainly benefit devices which currently handle unaligned accesses themselves. - Currently there aren't any qtests to cover the unaligned access cputlb path - How would using the memory API implementation interact with MemoryRegionOps .valid.unaligned and .impl.unaligned? - The current cputlb store_helper_unaligned() and also load_helper_unaligned() proposed by this patchset always use byte accesses, i.e they do not honour the target MemoryRegion min_access_size. Switching to the memory API could therefore cause some existing cases to break, although -d guest_errors should now log these. - Phil thinks that using the memory API could break ISA bus accesses ATB, Mark.