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=-2.3 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 BE7C6C3A5A2 for ; Sat, 24 Aug 2019 02:18:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9508E21726 for ; Sat, 24 Aug 2019 02:18:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726561AbfHXCSr (ORCPT ); Fri, 23 Aug 2019 22:18:47 -0400 Received: from mga04.intel.com ([192.55.52.120]:46088 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725924AbfHXCSr (ORCPT ); Fri, 23 Aug 2019 22:18:47 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 23 Aug 2019 19:18:46 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,422,1559545200"; d="scan'208";a="173655356" Received: from allen-box.sh.intel.com (HELO [10.239.159.136]) ([10.239.159.136]) by orsmga008.jf.intel.com with ESMTP; 23 Aug 2019 19:18:41 -0700 Cc: baolu.lu@linux.intel.com, David Woodhouse , Bjorn Helgaas , Christoph Hellwig , 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 v7 1/7] iommu/vt-d: Don't switch off swiotlb if use direct dma To: Joerg Roedel References: <20190823071735.30264-1-baolu.lu@linux.intel.com> <20190823071735.30264-2-baolu.lu@linux.intel.com> <20190823083956.GB24194@8bytes.org> From: Lu Baolu Message-ID: <8fb96c3b-c535-6d90-e1e1-c635aec6f178@linux.intel.com> Date: Sat, 24 Aug 2019 10:17:30 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190823083956.GB24194@8bytes.org> 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 Joerg, On 8/23/19 4:39 PM, Joerg Roedel wrote: > On Fri, Aug 23, 2019 at 03:17:29PM +0800, Lu Baolu wrote: >> --- a/drivers/iommu/intel-iommu.c >> +++ b/drivers/iommu/intel-iommu.c >> @@ -4569,9 +4569,6 @@ static int __init platform_optin_force_iommu(void) >> iommu_identity_mapping |= IDENTMAP_ALL; >> >> dmar_disabled = 0; >> -#if defined(CONFIG_X86) && defined(CONFIG_SWIOTLB) >> - swiotlb = 0; >> -#endif >> no_iommu = 0; >> >> return 1; >> @@ -4710,9 +4707,6 @@ int __init intel_iommu_init(void) >> } >> up_write(&dmar_global_lock); >> >> -#if defined(CONFIG_X86) && defined(CONFIG_SWIOTLB) >> - swiotlb = 0; >> -#endif > > So this will cause the 64MB SWIOTLB aperture to be allocated even when > there will never be an untrusted device in the system, right? I guess > this will break some kdump setups as they need to resize their low > memory allocations to make room for the aperture because of this > patch-set. Yes, you are right. I didn't consider the kdump case. > > But I also don't see a way around this for now as untrusted devices are > usually hotplugged and might not be present at boot. So we can't make > the decision about the allocation at boot time. If a system has any external port, through which an untrusted device might be connected, the external port itself should be marked as an untrusted device, and all devices beneath it just inherit this attribution. So during iommu driver initialization, we can easily know whether the system has (or potentially has) untrusted devices by iterating the device tree. I will add such check in the next version if no objections. > > But this mechanism needs to be moved to the dma-iommu implementation at > some point, and then we should allocate the bounce memory pages > on-demand. We can easily do this in page-size chunks and map them > together with iommu page-tables. This way we don't need to pre-allocate > a large memory-chunk at boot. > > Regards, > > Joerg Best regards, Baolu