linux-kernel - Re: [Xen-devel] crash tool - problem with new Xen linear virtual mapped sparse p2m list

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Message-ID: <20151124111725.4f45412e@hananiah.suse.cz>
Date:	Tue, 24 Nov 2015 11:17:25 +0100
From:	Petr Tesarik <ptesarik@...e.cz>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	Malcolm Crossley <malcolm.crossley@...rix.com>,
	Jan Beulich <JBeulich@...e.com>,
	Daniel Kiper <daniel.kiper@...cle.com>,
	Juergen Gross <JGross@...e.com>, <olaf@...fle.de>,
	<keir@....org>, <andrew.cooper3@...rix.com>,
	<linux-kernel@...r.kernel.org>, <dslutz@...izon.com>,
	<anderson@...hat.com>, David Mair <DMAIR@...e.com>,
	<xen-devel@...ts.xenproject.org>, <boris.ostrovsky@...cle.com>,
	<crash-utility@...hat.com>
Subject: Re: [Xen-devel] crash tool - problem with new Xen linear virtual
 mapped sparse p2m list

On Tue, 24 Nov 2015 10:09:01 +0000
David Vrabel <david.vrabel@...rix.com> 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, <JGross@...e.com> 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.

Petr T
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