Re: [Xen-devel] One question about the hypercall to translate gfn to mfn.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.12.14 at 07:25, <kevin.tian@xxxxxxxxx> wrote:
>>  From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> >>> On 12.12.14 at 08:24, <kevin.tian@xxxxxxxxx> wrote:
>> > - how is BFN or unused address (what do you mean by address here?)
>> > allocated? does it need present in guest physical memory at boot time,
>> > or just finding some holes?
>> 
>> Fitting this into holes should be fine.
> 
> this is an interesting open to be further discussed. Here we need consider 
> the extreme case, i.e. a 64bit GPU page table can legitimately use up all 
> the system memory allocates to that VM, and considering dozens of VMs, 
> it means we need reserve a very large hole. 

Oh, it's guest RAM you want mapped, not frame buffer space. But still
you're never going to have to map more than the total amount of host
RAM, and (with Linux) we already assume everything can be mapped
through the 1:1 mapping. I.e. the only collision would be with excessive
PFN reservations for ballooning purposes.

Jan


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