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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 9C686C31E5D for ; Tue, 18 Jun 2019 14:22:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7C309213F2 for ; Tue, 18 Jun 2019 14:22:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729529AbfFROWw (ORCPT ); Tue, 18 Jun 2019 10:22:52 -0400 Received: from foss.arm.com ([217.140.110.172]:43642 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726248AbfFROWu (ORCPT ); Tue, 18 Jun 2019 10:22:50 -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 EC3BD2B; Tue, 18 Jun 2019 07:22:49 -0700 (PDT) Received: from [10.1.196.129] (ostrya.cambridge.arm.com [10.1.196.129]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AC35F3F718; Tue, 18 Jun 2019 07:22:48 -0700 (PDT) Subject: Re: [PATCH 1/8] iommu: Add I/O ASID allocator To: Jacob Pan Cc: Jonathan Cameron , Mark Rutland , "devicetree@vger.kernel.org" , Will Deacon , "linux-kernel@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "robh+dt@kernel.org" , Robin Murphy , "linux-arm-kernel@lists.infradead.org" References: <20190610184714.6786-1-jean-philippe.brucker@arm.com> <20190610184714.6786-2-jean-philippe.brucker@arm.com> <20190611103625.00001399@huawei.com> <62d1f310-0cba-4d55-0f16-68bba3c64927@arm.com> <20190611111333.425ce809@jacob-builder> From: Jean-Philippe Brucker Message-ID: <13e19d8c-8918-a3bb-f398-2ac41c71d307@arm.com> Date: Tue, 18 Jun 2019 15:22:20 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190611111333.425ce809@jacob-builder> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/06/2019 19:13, Jacob Pan wrote: >>>> +/** >>>> + * ioasid_find - Find IOASID data >>>> + * @set: the IOASID set >>>> + * @ioasid: the IOASID to find >>>> + * @getter: function to call on the found object >>>> + * >>>> + * The optional getter function allows to take a reference to the >>>> found object >>>> + * under the rcu lock. The function can also check if the object >>>> is still valid: >>>> + * if @getter returns false, then the object is invalid and NULL >>>> is returned. >>>> + * >>>> + * If the IOASID has been allocated for this set, return the >>>> private pointer >>>> + * passed to ioasid_alloc. Private data can be NULL if not set. >>>> Return an error >>>> + * if the IOASID is not found or does not belong to the set. >>> >>> Perhaps should make it clear that @set can be null. >> >> Indeed. But I'm not sure allowing @set to be NULL is such a good idea, >> because the data type associated to an ioasid depends on its set. For >> example SVA will put an mm_struct in there, and auxiliary domains use >> some structure private to the IOMMU domain. >> > I am not sure we need to count on @set to decipher data type. Whoever > does the allocation and owns the IOASID should knows its own data type. > My thought was that @set is only used to group IDs, permission check > etc. > >> Jacob, could me make @set mandatory, or do you see a use for a global >> search? If @set is NULL, then callers can check if the return pointer >> is NULL, but will run into trouble if they try to dereference it. >> > A global search use case can be for PRQ. IOMMU driver gets a IOASID > (first interrupt then retrieve from a queue), it has no idea which > @set it belongs to. But the data types are the same for all IOASIDs > used by the IOMMU. They aren't when we use a generic SVA handler. Following a call to iommu_sva_bind_device(), iommu-sva.c allocates an IOASID and store an mm_struct. If auxiliary domains are also enabled for the device, following a call to iommu_aux_attach_device() the IOMMU driver allocates an IOASID and stores some private object. Now for example the IOMMU driver receives a PPR and calls ioasid_find() with @set = NULL. ioasid_find() may return either an mm_struct or a private object, and the driver cannot know which it is so the returned value is unusable. Thanks, Jean