Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753825AbbKXNqt (ORCPT ); Tue, 24 Nov 2015 08:46:49 -0500 Received: from smtp.citrix.com ([66.165.176.89]:47350 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753400AbbKXNqs convert rfc822-to-8bit (ORCPT ); Tue, 24 Nov 2015 08:46:48 -0500 X-IronPort-AV: E=Sophos;i="5.20,338,1444694400"; d="scan'208";a="314396575" Message-ID: <1448372770.26412.13.camel@citrix.com> Subject: Re: [Xen-devel] crash tool - problem with new Xen linear virtual mapped sparse p2m list From: Ian Campbell To: Andrew Cooper , Petr Tesarik , David Vrabel CC: Juergen Gross , , , "David Mair" , Daniel Kiper , , , , Jan Beulich , , "Malcolm Crossley" , , Date: Tue, 24 Nov 2015 13:46:10 +0000 In-Reply-To: <56543D57.2030903@citrix.com> 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> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.18.1-1 MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2362 Lines: 56 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. Ian. -- 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/