From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xunlei Pang Subject: Re: [PATCH] iommu/vt-d: Flush old iotlb for kdump when the device gets context mapped Date: Wed, 30 Nov 2016 16:15:23 +0800 Message-ID: <583E8A9B.7070906@redhat.com> References: <1479286950-21885-1-git-send-email-xlpang@redhat.com> <582C232F.6080205@redhat.com> <582D1A40.409@redhat.com> <20161129143547.GG2078@8bytes.org> Reply-To: xlpang-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20161129143547.GG2078-zLv9SwRftAIdnm+yROfE0A@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Joerg Roedel , xlpang-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org Cc: Don Brace , Myron Stowe , kexec-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, LKML , iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, Dave Young , David Woodhouse List-Id: iommu@lists.linux-foundation.org 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 >