From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753289Ab1KAJup (ORCPT ); Tue, 1 Nov 2011 05:50:45 -0400 Received: from mx1.redhat.com ([209.132.183.28]:21884 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753069Ab1KAJuo (ORCPT ); Tue, 1 Nov 2011 05:50:44 -0400 Message-ID: <4EAFC15C.7010601@redhat.com> Date: Tue, 01 Nov 2011 17:52:28 +0800 From: Dave Young User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.15) Gecko/20110323 Thunderbird/3.1.9 MIME-Version: 1.0 To: David Woodhouse CC: kexec@lists.infradead.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, vgoyal@redhat.com, horms@verge.net.au, luyu@redhat.com Subject: Re: [PATCH retry] intel-iommu:make identity_map default for crash dump References: <20111101091939.GA8985@darkstar.nay.redhat.com> <1320140052.2089.5.camel@shinybook.infradead.org> In-Reply-To: <1320140052.2089.5.camel@shinybook.infradead.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/01/2011 05:34 PM, David Woodhouse wrote: > On Tue, 2011-11-01 at 17:19 +0800, Dave Young wrote: >> kdump kernel sometimes will get DMAR faults which >> is caused by random in-flight dma from 1st kernel >> >> Here make the identity_mapping as default for this case > > So you want to *allow* the random in-flight DMA? And with an identity > mapping it's really going to random addresses, since it'll be > untranslated and won't even go to the physical addresses which it was > originally intended for? > > This seems entirely broken to me. > > If there is "random in-flight dma" from the first kernel, the correct > thing to do is *block* it. Which is what we do. > This patch works for me for several cases. For kdump It can be seen a workaround. But yes blocking the 1st kernel dma is ideal. Glad to hear that you are working on this. -- Thanks Dave