From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751713AbdGaK3a (ORCPT ); Mon, 31 Jul 2017 06:29:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48474 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750920AbdGaK33 (ORCPT ); Mon, 31 Jul 2017 06:29:29 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 8CF80769E2 Authentication-Results: ext-mx03.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx03.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=bhe@redhat.com Date: Mon, 31 Jul 2017 18:29:25 +0800 From: Baoquan He To: Joerg Roedel Cc: iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v8 10/13] iommu/amd: Allocate memory below 4G for dev table if translation pre-enabled Message-ID: <20170731102925.GA9999@x1> References: <1500627551-12930-1-git-send-email-bhe@redhat.com> <1500627551-12930-11-git-send-email-bhe@redhat.com> <20170727155550.GO3610@suse.de> <20170728090619.GM24304@x1> <20170731101530.GB29157@x1> <20170731102153.GK3431@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170731102153.GK3431@suse.de> User-Agent: Mutt/1.7.0 (2016-08-17) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Mon, 31 Jul 2017 10:29:29 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/31/17 at 12:21pm, Joerg Roedel wrote: > Hi Baoquan, > > On Mon, Jul 31, 2017 at 06:15:30PM +0800, Baoquan He wrote: > > I plan to add GFP_DMA32 when allocate amd_iommu_dev_table in > > early_amd_iommu_init() as below. Then in kdump kernel we don't need to > > worry if the old amd_iommu_dev_table could be above 4G, right? And might > > not need to check if it's above 4G, right? > > > > diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c > > index 781a138..85d6445 100644 > > --- a/drivers/iommu/amd_iommu_init.c > > +++ b/drivers/iommu/amd_iommu_init.c > > @@ -2436,7 +2436,8 @@ static int __init early_amd_iommu_init(void) > > > > /* Device table - directly used by all IOMMUs */ > > ret = -ENOMEM; > > - amd_iommu_dev_table = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, > > + amd_iommu_dev_table = (void *)__get_free_pages( > > + GFP_KERNEL | __GFP_ZERO | GFP_DMA32, > > get_order(dev_table_size)); > > if (amd_iommu_dev_table == NULL) > > goto out; > > Yeah, adding GFP_DMA32 is right. But you still need to check it in the > kdump path. Not checking it would mean you trust the old kernel, but > since it paniced there is no reason to put any trust in what happened > before. You are right, it could be touched accidentally. It must be checked. Thanks a lot for your answer!