Re: [Xen-devel] "Iomem mapping not permitted" during windows crash dump under GPLPV

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 02.02.10 14:30 >>>
>On 02/02/2010 11:27, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>
>>>>> "James Harper" <james.harper@xxxxxxxxxxxxxxxx> 02.02.10 12:07 >>>
>>> Someone on the ntdev list suggested that one approach could be to
>>> allocate a single page at setup time and map that into each 'hole' I
>>> leave behind by ballooning pages out. I haven't checked if Xen supports
>>> a HVM DomU randomly mapping pages like that and if it will let it map
>>> the same page multiple times, but it would remove the errors and keep
>>> everything happy.
>> 
>> There is no question - it just has to support this. Linux would not work
>> without this (nor can I imagine any other OS would).
>
>I don't think a page can be simultaneously mapped at multiple locations in a
>guest's p2m though.

Aren't we talking about HVM guests here? If the guest maps a page, it
doesn't know about the p2m. Likewise the balloon driver doesn't care
about that table (and would install the mapping as James suggested
instead of the [in the Linux balloon driver] pv-guest-only clearing of
the respective 1:1 mapping page table entry). The main problem I
would see him possibly having is that he might need to break up large
pages, but otoh I'm not even sure Windows has a 1:1 mapping.

Confused, Jan


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