From mboxrd@z Thu Jan  1 00:00:00 1970
From: Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [PATCH v5 4/9] xen: introduce XEN_DOMCTL_devour
Date: Tue, 13 Jan 2015 17:17:22 +0100
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To: Ian Campbell <Ian.Campbell@citrix.com>, Jan Beulich <jbeulich@suse.com>
Cc: Wei Liu <wei.liu2@citrix.com>, Andrew Jones <drjones@redhat.com>, Julien Grall <julien.grall@linaro.org>, Keir Fraser <keir@xen.org>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Ian Jackson <ian.jackson@eu.citrix.com>, Tim Deegan <tim@xen.org>, Olaf Hering <olaf@aepfle.de>, David Vrabel <david.vrabel@citrix.com>, Andrew Cooper <andrew.cooper3@citrix.com>, xen-devel@lists.xenproject.org
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Ian Campbell <Ian.Campbell@citrix.com> writes:

> On Thu, 2014-12-11 at 14:45 +0100, Vitaly Kuznetsov wrote:
>> +            gmfn = mfn_to_gmfn(d, mfn);
>
> (I haven't thought about it super hard, but I'm taking it as given that
> this approach to kexec is going to be needed for ARM too, since that
> seems likely)
>
> mfn_to_gmfn is going to be a bit pricey on ARM, we don't have an m2p to
> refer to, I'm not sure what we would do instead, walking the p2m looking
> for mfns surely won't be a good idea!

Can we form a 'temporary m2p' table by walking p2m once? Our domain is
dying and mappings don't change.

>
> An alternative approach to this might be to walk the guest p2m (with
> appropriate continuations) and move each domheap page (this would also
> help us preserve super page mappings). It would also have the advantage
> of not needing additional stages in the destroy path and state in struct
> domain etc, since all the action would be constrained to the one
> hypercall.

Something like that (but not exactly) was in my RFC/WIPv2 series:
http://lists.xen.org/archives/html/xen-devel/2014-09/msg03624.html

The drawback of such approach is the necessity of copying all mapped
more than once pages (granted pages, qemu-mapped pages, ...) or at least
providing blank pages instead of them. 

Jan, may I also explicitly ask your opinion?

-- 
  Vitaly