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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 679C8C07E9E for ; Tue, 6 Jul 2021 15:39:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 531C661A13 for ; Tue, 6 Jul 2021 15:39:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232596AbhGFPmH (ORCPT ); Tue, 6 Jul 2021 11:42:07 -0400 Received: from foss.arm.com ([217.140.110.172]:45252 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232291AbhGFPmF (ORCPT ); Tue, 6 Jul 2021 11:42:05 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D04E3106F; Tue, 6 Jul 2021 08:39:26 -0700 (PDT) Received: from [10.57.40.45] (unknown [10.57.40.45]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 793C53F73B; Tue, 6 Jul 2021 08:39:19 -0700 (PDT) Subject: Re: [PATCH v15 06/12] swiotlb: Use is_swiotlb_force_bounce for swiotlb data bouncing To: Christoph Hellwig Cc: Will Deacon , heikki.krogerus@linux.intel.com, thomas.hellstrom@linux.intel.com, peterz@infradead.org, benh@kernel.crashing.org, joonas.lahtinen@linux.intel.com, dri-devel@lists.freedesktop.org, chris@chris-wilson.co.uk, grant.likely@arm.com, paulus@samba.org, Frank Rowand , mingo@kernel.org, Stefano Stabellini , Saravana Kannan , mpe@ellerman.id.au, "Rafael J . Wysocki" , Bartosz Golaszewski , bskeggs@redhat.com, linux-pci@vger.kernel.org, xen-devel@lists.xenproject.org, Thierry Reding , intel-gfx@lists.freedesktop.org, matthew.auld@intel.com, linux-devicetree , Jianxiong Gao , Daniel Vetter , Konrad Rzeszutek Wilk , maarten.lankhorst@linux.intel.com, airlied@linux.ie, Dan Williams , linuxppc-dev@lists.ozlabs.org, jani.nikula@linux.intel.com, Nathan Chancellor , Rob Herring , rodrigo.vivi@intel.com, Bjorn Helgaas , Claire Chang , boris.ostrovsky@oracle.com, Andy Shevchenko , jgross@suse.com, Nicolas Boichat , Greg KH , Randy Dunlap , Qian Cai , lkml , "list@263.net:IOMMU DRIVERS" , Jim Quinlan , xypron.glpk@gmx.de, Tom Lendacky , bauerman@linux.ibm.com References: <20210701074045.GA9436@willie-the-truck> <20210702135856.GB11132@willie-the-truck> <0f7bd903-e309-94a0-21d7-f0e8e9546018@arm.com> <20210705190352.GA19461@willie-the-truck> <20210706044848.GA13640@lst.de> <20210706132422.GA20327@willie-the-truck> <20210706140513.GA26498@lst.de> From: Robin Murphy Message-ID: Date: Tue, 6 Jul 2021 16:39:11 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210706140513.GA26498@lst.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-07-06 15:05, Christoph Hellwig wrote: > On Tue, Jul 06, 2021 at 03:01:04PM +0100, Robin Murphy wrote: >> FWIW I was pondering the question of whether to do something along those >> lines or just scrap the default assignment entirely, so since I hadn't got >> round to saying that I've gone ahead and hacked up the alternative >> (similarly untested) for comparison :) >> >> TBH I'm still not sure which one I prefer... > > Claire did implement something like your suggestion originally, but > I don't really like it as it doesn't scale for adding multiple global > pools, e.g. for the 64-bit addressable one for the various encrypted > secure guest schemes. Ah yes, that had slipped my mind, and it's a fair point indeed. Since we're not concerned with a minimal fix for backports anyway I'm more than happy to focus on Will's approach. Another thing is that that looks to take us a quiet step closer to the possibility of dynamically resizing a SWIOTLB pool, which is something that some of the hypervisor protection schemes looking to build on top of this series may want to explore at some point. Robin.