From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932939AbdLROiG (ORCPT ); Mon, 18 Dec 2017 09:38:06 -0500 Received: from mail.skyhub.de ([5.9.137.197]:38510 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932734AbdLROiB (ORCPT ); Mon, 18 Dec 2017 09:38:01 -0500 Date: Mon, 18 Dec 2017 15:37:53 +0100 From: Borislav Petkov To: Baoquan He Cc: Jiri Bohac , Toshi Kani , David Airlie , Dave Young , joro@8bytes.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Ingo Molnar , "H. Peter Anvin" , Bjorn Helgaas , Thomas Gleixner , yinghai@kernel.org, Vivek Goyal Subject: Re: [PATCH v2] x86/kexec: Exclude GART aperture from vmcore Message-ID: <20171218143753.k7xyq6yiyjisnonh@pd.tnic> References: <20171216001514.x5eg37ad4aa2fwqt@dwarf.suse.cz> <20171216010142.GK12442@x1> <20171217214735.nuxq5zo2eknqpbpi@pd.tnic> <20171218134736.GA4035@x1> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20171218134736.GA4035@x1> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 18, 2017 at 09:47:36PM +0800, Baoquan He wrote: > pr_info("Your BIOS doesn't leave an aperture memory hole\n"); > pr_info("Please enable the IOMMU option in the BIOS setup\n"); > pr_info("This costs you %dMB of RAM\n", > 32 << fallback_aper_order); > ... > } There are BIOSen where there's not even an IOMMU option to enable in the first place. So forget fixing the firmware. > Previously people added gart region to iomem to notice that even though > there's ram mapped, while it's occupied by gart, please don't dump it. > Later it's reverted commit 707d4eefbdb3 ("Revert [PATCH] Insert GART > region into resource map"). Yes, I read Jiri's commit message, TYVM. > The other is not to tell kdump kernel that there's ram mapped into the > region. In the mail I replied to Jiri's v1 post, I meant the 2nd way. > Remove the ram region occupied by gart from iomem, then kdump kernel > won't see it and won't dump it. That's the wrong approach. Because this way you're lying in iomem about the layout by hiding the gart range. What needs to happen is to *exclude* the region from the dumping side only, so that it doesn't touch it. Because the second kernel still needs to show a *correct* iomem ranges list. Imagine someone looks at it during debugging... So I think Jiri's approach is the right thing to do. -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.