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 9BA7CC43218 for ; Tue, 11 Jun 2019 14:35:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 68D272145D for ; Tue, 11 Jun 2019 14:35:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390359AbfFKOfu (ORCPT ); Tue, 11 Jun 2019 10:35:50 -0400 Received: from foss.arm.com ([217.140.110.172]:34402 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388292AbfFKOfu (ORCPT ); Tue, 11 Jun 2019 10:35:50 -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 6932D337; Tue, 11 Jun 2019 07:35:49 -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 28CF33F557; Tue, 11 Jun 2019 07:35:48 -0700 (PDT) From: Jean-Philippe Brucker Subject: Re: [PATCH 1/8] iommu: Add I/O ASID allocator To: Jonathan Cameron Cc: mark.rutland@arm.com, devicetree@vger.kernel.org, will.deacon@arm.com, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, robh+dt@kernel.org, robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org, "jacob.jun.pan@linux.intel.com" References: <20190610184714.6786-1-jean-philippe.brucker@arm.com> <20190610184714.6786-2-jean-philippe.brucker@arm.com> <20190611103625.00001399@huawei.com> Message-ID: <62d1f310-0cba-4d55-0f16-68bba3c64927@arm.com> Date: Tue, 11 Jun 2019 15:35:22 +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: <20190611103625.00001399@huawei.com> Content-Type: text/plain; charset=utf-8 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 10:36, Jonathan Cameron wrote: >> +/** >> + * ioasid_alloc - Allocate an IOASID >> + * @set: the IOASID set >> + * @min: the minimum ID (inclusive) >> + * @max: the maximum ID (inclusive) >> + * @private: data private to the caller >> + * >> + * Allocate an ID between @min and @max. The @private pointer is stored >> + * internally and can be retrieved with ioasid_find(). >> + * >> + * Return: the allocated ID on success, or %INVALID_IOASID on failure. >> + */ >> +ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max, >> + void *private) >> +{ >> + u32 id = INVALID_IOASID; >> + struct ioasid_data *data; >> + >> + data = kzalloc(sizeof(*data), GFP_KERNEL); >> + if (!data) >> + return INVALID_IOASID; >> + >> + data->set = set; >> + data->private = private; >> + >> + if (xa_alloc(&ioasid_xa, &id, data, XA_LIMIT(min, max), GFP_KERNEL)) { >> + pr_err("Failed to alloc ioasid from %d to %d\n", min, max); >> + goto exit_free; >> + } >> + data->id = id; >> + >> +exit_free: > > This error flow is perhaps a little more confusing than it needs to be? > > My assumption (perhaps wrong) is that we only have an id == INVALID_IOASID > if the xa_alloc fails, and that we will always have such an id value if > it does (I'm not totally sure this second element is true in __xa_alloc). > > If I'm missing something perhaps a comment on how else we'd get here. Yes we can simplify this: return id; exit_free: kfree(data) return INVALID_IOASID; } The XA API doesn't say that @id passed to xa_alloc() won't be modified in case of error. It's true in the current implementation, but won't necessarily stay that way. On the other hand I think it's safe to expect @id to always be set when xa_alloc() succeeds. >> +/** >> + * 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. 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. > >> + */ >> +void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid, >> + bool (*getter)(void *)) >> +{ >> + void *priv = NULL; > > Set in all paths, so does need to be set here. Right Thanks, Jean