From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1423390AbcBQOAo (ORCPT ); Wed, 17 Feb 2016 09:00:44 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:35370 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1423069AbcBQOAn (ORCPT ); Wed, 17 Feb 2016 09:00:43 -0500 Date: Wed, 17 Feb 2016 14:59:23 +0100 From: Daniel Kiper To: Juergen Gross Cc: boris.ostrovsky@oracle.com, david.vrabel@citrix.com, konrad.wilk@oracle.com, crash-utility@redhat.com, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org Subject: Re: p2m stuff and crash tool Message-ID: <20160217135923.GU3482@olila.local.net-space.pl> References: <20160216113556.GS3482@olila.local.net-space.pl> <56C31C45.30408@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56C31C45.30408@suse.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 16, 2016 at 01:55:33PM +0100, Juergen Gross wrote: > Hi Daniel, > > On 16/02/16 12:35, Daniel Kiper wrote: > > Hey Juergen, [...] > > After that I decided to take a look at Linux kernel upstream. I saw > > that xen_max_p2m_pfn in xen_build_mfn_list_list() is equal to "the > > end of last usable machine memory region available for a given > > dom0_mem argument + something", e.g. > > > > For dom0_mem=1g,max:1g: > > > > (XEN) Xen-e820 RAM map: > > (XEN) 0000000000000000 - 000000000009fc00 (usable) > > (XEN) 000000000009fc00 - 00000000000a0000 (reserved) > > (XEN) 00000000000f0000 - 0000000000100000 (reserved) > > (XEN) 0000000000100000 - 000000007ffdf000 (usable) <--- HERE > > (XEN) 000000007ffdf000 - 0000000080000000 (reserved) > > (XEN) 00000000b0000000 - 00000000c0000000 (reserved) > > (XEN) 00000000feffc000 - 00000000ff000000 (reserved) > > (XEN) 00000000fffc0000 - 0000000100000000 (reserved) > > (XEN) 0000000100000000 - 0000000180000000 (usable) > > > > Hence xen_max_p2m_pfn == 0x80000 > > > > Later I reviewed most of your p2m related commits and I realized > > that you played whack-a-mole game with p2m bugs. Sadly, I was not > > able to identify exactly one (or more) commit which would fix the > > same issue (well, there are some which fixes similar stuff but not > > the same one described above). So, if you explain to me why > > xen_max_p2m_pfn is set to that value and does not e.g. max_pfn then > > it will be much easier for me to write proper fix and maybe fix > > the same issue in upstream kernel if it is needed (well, crash > > tool does not work with new p2m layout so first of all I must fix it; > > I hope that you will help me to that sooner or later). > > The reason for setting xen_max_p2m_pfn to nr_pages initially is it's > usage in __pfn_to_mfn(): this must work with the initial p2m list > supplied by the hypervisor which just has only nr_pages entries. That make sense. > Later it is updated to the number of entries the linear p2m list is > able to hold. This size has to include possible hotplugged memory > in prder to be able to make use of that memory later (remember: the > p2m list's size is limited by the virtual space allocated for it via > xen_vmalloc_p2m_tree()). However, I have memory hotplug disabled and kernel set xen_max_p2m_pfn to 0x80000 (2 Gib) even if dom0 memory was set to 1 GiB. Hmmm... Why? I suppose that if xen_max_p2m_pfn == max_pfn then everything should work. Am I missing something? Daniel