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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 4F929C7618B for ; Thu, 25 Jul 2019 07:18:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0F59C21734 for ; Thu, 25 Jul 2019 07:18:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387868AbfGYHSn (ORCPT ); Thu, 25 Jul 2019 03:18:43 -0400 Received: from mga09.intel.com ([134.134.136.24]:21527 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387562AbfGYHSm (ORCPT ); Thu, 25 Jul 2019 03:18:42 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 25 Jul 2019 00:18:42 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,305,1559545200"; d="scan'208";a="181373984" Received: from allen-box.sh.intel.com (HELO [10.239.159.136]) ([10.239.159.136]) by orsmga002.jf.intel.com with ESMTP; 25 Jul 2019 00:18:37 -0700 Cc: baolu.lu@linux.intel.com, David Woodhouse , Joerg Roedel , Bjorn Helgaas , ashok.raj@intel.com, jacob.jun.pan@intel.com, alan.cox@intel.com, kevin.tian@intel.com, mika.westerberg@linux.intel.com, Ingo Molnar , Greg Kroah-Hartman , pengfei.xu@intel.com, Konrad Rzeszutek Wilk , Marek Szyprowski , Robin Murphy , Jonathan Corbet , Boris Ostrovsky , Juergen Gross , Stefano Stabellini , Steven Rostedt , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Jacob Pan Subject: Re: [PATCH v5 02/10] iommu/vt-d: Use per-device dma_ops To: Christoph Hellwig References: <20190725031717.32317-1-baolu.lu@linux.intel.com> <20190725031717.32317-3-baolu.lu@linux.intel.com> <20190725054413.GC24527@lst.de> From: Lu Baolu Message-ID: Date: Thu, 25 Jul 2019 15:18:03 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190725054413.GC24527@lst.de> Content-Type: text/plain; charset=utf-8; format=flowed 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 Hi Christoph, On 7/25/19 1:44 PM, Christoph Hellwig wrote: >> /* Check if the dev needs to go through non-identity map and unmap process.*/ >> static bool iommu_need_mapping(struct device *dev) >> { >> - int ret; >> - >> if (iommu_dummy(dev)) >> return false; >> >> - ret = identity_mapping(dev); >> - if (ret) { >> - u64 dma_mask = *dev->dma_mask; >> - >> - if (dev->coherent_dma_mask && dev->coherent_dma_mask < dma_mask) >> - dma_mask = dev->coherent_dma_mask; >> - >> - if (dma_mask >= dma_get_required_mask(dev)) >> - return false; > > Don't we need to keep this bit so that we still allow the IOMMU > to act if the device has a too small DMA mask to address all memory in > the system, even if if it should otherwise be identity mapped? > This checking happens only when device is using an identity mapped domain. If the device has a small DMA mask, swiotlb will be used for high memory access. This is supposed to be handled in dma_direct_map_page(): if (unlikely(!dma_direct_possible(dev, dma_addr, size)) && !swiotlb_map(dev, &phys, &dma_addr, size, dir, attrs)) { report_addr(dev, dma_addr, size); return DMA_MAPPING_ERROR; } Best regards, Baolu