Re: [Xen-devel] [PATCH v5 4/9] xen: introduce XEN_DOMCTL_devour

[Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>]

Ian Campbell <Ian.Campbell@xxxxxxxxxx> 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

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