Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754185AbbKXNjW (ORCPT ); Tue, 24 Nov 2015 08:39:22 -0500 Received: from prv-mh.provo.novell.com ([137.65.248.74]:48359 "EHLO prv-mh.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753230AbbKXNjT (ORCPT ); Tue, 24 Nov 2015 08:39:19 -0500 Message-Id: <5654769502000078000B86AA@prv-mh.provo.novell.com> X-Mailer: Novell GroupWise Internet Agent 14.0.1 Date: Tue, 24 Nov 2015 06:39:17 -0700 From: "Jan Beulich" To: "Petr Tesarik" Cc: , "Andrew Cooper" , "David Vrabel" , "Malcolm Crossley" , , , "DanielKiper" , , , "David Mair" , "Juergen Gross" , , , Subject: Re: [Xen-devel] crash tool - problem with new Xen linear virtual mapped sparse p2m list References: <20151123201830.GN4768@olila.local.net-space.pl> <565409DA.90908@suse.com> <565434F102000078000B8424@prv-mh.provo.novell.com> <56543412.7090104@citrix.com> <5654373D.9070403@citrix.com> <20151124111725.4f45412e@hananiah.suse.cz> <56543D57.2030903@citrix.com> <20151124135701.1d75c901@hananiah.suse.cz> In-Reply-To: <20151124135701.1d75c901@hananiah.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2460 Lines: 53 >>> On 24.11.15 at 13:57, wrote: > V Tue, 24 Nov 2015 10:35:03 +0000 > Andrew Cooper napsáno: > >> On 24/11/15 10:17, Petr Tesarik wrote: >> > On Tue, 24 Nov 2015 10:09:01 +0000 >> > David Vrabel wrote: >> > >> >> On 24/11/15 09:55, Malcolm Crossley wrote: >> >>> On 24/11/15 08:59, Jan Beulich wrote: >> >>>>>>> On 24.11.15 at 07:55, wrote: >> >>>>> What about: >> >>>>> >> >>>>> 4) Instead of relying on the kernel maintained p2m list for m2p >> >>>>> conversion use the hypervisor maintained m2p list which should be >> >>>>> available in the dump as well. This is the way the alive kernel is >> >>>>> working, so mimic it during crash dump analysis. >> >>>> I fully agree; I have to admit that looking at the p2m when doing page >> >>>> table walks for a PV Dom0 (having all machine addresses in page table >> >>>> entries) seems kind of backwards. (But I say this knowing nothing >> >>>> about the tool.) >> >>>> >> >>> I don't think we can reliably use the m2p for PV domains because >> >>> PV domains don't always issue a m2p update hypercall when they change >> >>> their p2m mapping. >> >> This only applies to foreign pages which won't be very interesting to a >> >> crash tool. >> > True. I think the main reason crash hasn't done this is that it cannot >> > find the hypervisor maintained m2p list. It should be sufficient to add >> > some more fields to XEN_VMCOREINFO, so that crash can locate the >> > mapping in the dump. >> >> The M2P lives at an ABI-specified location in all virtual address spaces >> for PV guests. >> >> Either 0xF5800000 or 0xFFFF800000000000 depending on bitness. > > Hm, this is nice, but kind of chicken-and-egg problem. A system dump > contains a snapshot of the machine's RAM. But the addresses you > mentioned are virtual addresses. How do I translate them to physical > addresses without an m2p mapping? I need at least the value of CR3 for > that domain, and most likely a way to determine if it is a PV domain. This ought to also be present in Xen's master page table (idle_pg_table[]), and I suppose we can take for granted a symbol table being available. Jan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/