Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932403AbcK3IOY (ORCPT ); Wed, 30 Nov 2016 03:14:24 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54204 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932233AbcK3IOR (ORCPT ); Wed, 30 Nov 2016 03:14:17 -0500 Reply-To: xlpang@redhat.com Subject: Re: [PATCH] iommu/vt-d: Flush old iotlb for kdump when the device gets context mapped References: <1479286950-21885-1-git-send-email-xlpang@redhat.com> <582C232F.6080205@redhat.com> <582D1A40.409@redhat.com> <20161129143547.GG2078@8bytes.org> To: Joerg Roedel , xlpang@redhat.com Cc: Myron Stowe , iommu@lists.linux-foundation.org, Don Brace , Dave Young , kexec@lists.infradead.org, LKML , Myron Stowe , David Woodhouse From: Xunlei Pang Message-ID: <583E8A9B.7070906@redhat.com> Date: Wed, 30 Nov 2016 16:15:23 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <20161129143547.GG2078@8bytes.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Wed, 30 Nov 2016 08:14:16 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1822 Lines: 41 On 11/29/2016 at 10:35 PM, Joerg Roedel wrote: > On Thu, Nov 17, 2016 at 10:47:28AM +0800, Xunlei Pang wrote: >> As per the comment, the code here only needs to flush context caches >> for the special domain 0 which is used to tag the >> non-present/erroneous caches, seems we should flush the old domain id >> of present entries for kdump according to the analysis, other than the >> new-allocated domain id. Let me ponder more on this. > Flushing the context entry only is fine. The old domain-id will not be > re-used anyway, so there is no point in reading it out of the context > table and flush it. Do you mean to flush the context entry using the new-allocated domain id? Yes, old domain-id will not be re-used as they were reserved when copy, but may still be cached by in-flight DMA access. Here is what the things seem to be from my understanding, and why I want to flush using the old domain id: 1) In kdump mode, old tables are copied, and all the iommu caches are flushed. 2) There comes some in-flight DMA before the device's new context is mapped, so translation caches(context, iotlb, etc) are created tagging old domain-id in the iommu hardware. 3) At the driver probe stage, the device is reset , and no in-flight DMA will exist. Here I assumed that the device reset won't flush the old caches in the iommu hardware related to this device. I haven't found any relevant specification, please correct me if I am wrong. 4) Then new context is setup, and new DMA is initiated, hit old cache that was created in 2) as currently there's no such flush action, so DMAR fault happens. I already posted v2 to flush context/iotlb using the old domain-id: https://lkml.org/lkml/2016/11/18/514 Regards, Xunlei > > Also, please add a Fixes-tag when you re-post this patch. > > > Joerg >