From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754715Ab3C0Kb0 (ORCPT ); Wed, 27 Mar 2013 06:31:26 -0400 Received: from 8bytes.org ([85.214.48.195]:47219 "EHLO mail.8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750716Ab3C0KbZ (ORCPT ); Wed, 27 Mar 2013 06:31:25 -0400 Date: Wed, 27 Mar 2013 11:31:22 +0100 From: Joerg Roedel To: Takao Indoh Cc: linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, dwmw2@infradead.org, kexec@lists.infradead.org Subject: Re: [PATCH] intel-iommu: Synchronize gcmd value with global command register Message-ID: <20130327103122.GK30540@8bytes.org> References: <1363829556-2128-1-git-send-email-indou.takao@jp.fujitsu.com> <20130326144629.GB2727@8bytes.org> <51527D74.9080209@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51527D74.9080209@jp.fujitsu.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-DSPAM-Result: Whitelisted X-DSPAM-Processed: Wed Mar 27 11:31:23 2013 X-DSPAM-Confidence: 0.9985 X-DSPAM-Probability: 0.0000 X-DSPAM-Signature: 5152ca7b23673325315251 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 27, 2013 at 02:02:44PM +0900, Takao Indoh wrote: > The root cause of this problem is mismatch between iommu->gcmd and > global command register in the case of kdump. At boot time, initial > value of iommu->gcmd is zero as I wrote above, but actual global command > register is *not* zero because some bits like IRE/TE/QIE are already set > in *first* kernel. Therefore this patch synchronize them to fix this > problem. Ok, I understand, but I still don't see why this is a problem. There is no point for the kdump kernel to preserve hardware state from the previous kernel. So I think the way it is implemented is correct. Joerg