Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754239AbbKXNzp (ORCPT ); Tue, 24 Nov 2015 08:55:45 -0500 Received: from prv-mh.provo.novell.com ([137.65.248.74]:49871 "EHLO prv-mh.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752912AbbKXNzn convert rfc822-to-8bit (ORCPT ); Tue, 24 Nov 2015 08:55:43 -0500 Message-Id: <56547A6C02000078000B86EB@prv-mh.provo.novell.com> X-Mailer: Novell GroupWise Internet Agent 14.0.1 Date: Tue, 24 Nov 2015 06:55:40 -0700 From: "Jan Beulich" To: "Ian Campbell" , "Petr Tesarik" Cc: , "Andrew Cooper" , "David Vrabel" , "MalcolmCrossley" , , , "Daniel Kiper" , , , "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> <1448372770.26412.13.camel@citrix.com> In-Reply-To: <1448372770.26412.13.camel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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: 2595 Lines: 61 >>> On 24.11.15 at 14:46, wrote: > On Tue, 2015-11-24 at 10:35 +0000, Andrew Cooper wrote: >> 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. > > In theory it can actually be dynamic. XENMEM_machphys_mapping is the way to > get at it (for both bitnesses). > > For 64-bit guests I think that is most an "in theory" thing and it never > has actually been so. > > For a 32-bit guest case I don't recall if it is just a 32on32 vs 32on64 > thing, or if something (either guest or toolstack) gets to pick more > dynamically or even if it is a dom0 vs domU thing. It's only for 32-on-64 where this range can change (and there it's the 64-bit address that crash would care about anyway). 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/