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=-10.0 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 7D653C3A59E for ; Wed, 21 Aug 2019 15:19:24 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (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 5D8C6216F4 for ; Wed, 21 Aug 2019 15:19:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5D8C6216F4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id AE671EDA; Wed, 21 Aug 2019 15:19:23 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id B6868EB6 for ; Wed, 21 Aug 2019 15:19:21 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp1.linuxfoundation.org (Postfix) with ESMTP id 67B7AE6 for ; Wed, 21 Aug 2019 15:19:21 +0000 (UTC) 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 0F3DD360; Wed, 21 Aug 2019 08:19:21 -0700 (PDT) Received: from fuggles.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 273933F718; Wed, 21 Aug 2019 08:19:20 -0700 (PDT) From: Will Deacon To: iommu@lists.linux-foundation.org Subject: [PATCH v2 1/8] iommu/arm-smmu-v3: Document ordering guarantees of command insertion Date: Wed, 21 Aug 2019 16:17:42 +0100 Message-Id: <20190821151749.23743-2-will@kernel.org> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20190821151749.23743-1-will@kernel.org> References: <20190821151749.23743-1-will@kernel.org> Cc: Jean-Philippe Brucker , Will Deacon , Robin Murphy X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org It turns out that we've always relied on some subtle ordering guarantees when inserting commands into the SMMUv3 command queue. With the recent changes to elide locking when possible, these guarantees become more subtle and even more important. Add a comment documented the barrier semantics of command insertion so that we don't have to derive the behaviour from scratch each time it comes up on the list. Signed-off-by: Will Deacon --- drivers/iommu/arm-smmu-v3.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c index b36a99971401..3402b1bc8e94 100644 --- a/drivers/iommu/arm-smmu-v3.c +++ b/drivers/iommu/arm-smmu-v3.c @@ -1286,6 +1286,22 @@ static void arm_smmu_cmdq_write_entries(struct arm_smmu_cmdq *cmdq, u64 *cmds, } } +/* + * This is the actual insertion function, and provides the following + * ordering guarantees to callers: + * + * - There is a dma_wmb() before publishing any commands to the queue. + * This can be relied upon to order prior writes to data structures + * in memory (such as a CD or an STE) before the command. + * + * - On completion of a CMD_SYNC, there is a control dependency. + * This can be relied upon to order subsequent writes to memory (e.g. + * freeing an IOVA) after completion of the CMD_SYNC. + * + * - Command insertion is totally ordered, so if two CPUs each race to + * insert their own list of commands then all of the commands from one + * CPU will appear before any of the commands from the other CPU. + */ static int arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu, u64 *cmds, int n, bool sync) { -- 2.11.0 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu