Re: [Xen-devel] Re: pvclock in userland (reprise)

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> Jeremy Fitzhardinge <jeremy@xxxxxxxx> 19.09.09 02:33 >>>
>On 09/18/09 01:06, Keir Fraser wrote:
>> On 18/09/2009 08:29, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>>
>>   
>>>> I don't think mapping things into application address space is really
>>>> possible without guest kernel changes. The guest kernel owns and manages 
>>>> the
>>>> pte that you'd be overwriting. Just blatting the pte would not be good 
>>>> form.
>>>>       
>>> Unless they sit in Xen's virtual space.
>>>     
>> Oh yes, I remember we talked about that before. That is possible, but the
>> design fell down on other points. I think guest kernel involvement, even if
>> only as a kernel driver, should make this more tractable.
>>   
>
>Xen's memory isn't mappable in a 32-bit compat domain, so you'd need to
>come up with something else there.

Why not?

>Does Xen still claim the top part of the 32-bit address space?

Sure - currently just for the compat M2P table. I can't see why other
things could be mapped there (the compat M2P table is at most 128M
in size, hence there's plenty of virtual space available).

Jan


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