Re: [Xen-devel] [PATCH v3 3/3] tools: introduce parameter max_wp_ram_ranges.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.02.16 at 14:47, <Paul.Durrant@xxxxxxxxxx> wrote:
>> From: Ian Jackson [mailto:Ian.Jackson@xxxxxxxxxxxxx]
>> Sent: 04 February 2016 13:34
>>  * Is it possible for libxl to somehow tell from the rest of the
>>    configuration that this larger limit should be applied ?
>> 
>>    AFAICT there is nothing in libxl directly involving vgpu.  How can
>>    libxl be used to create a guest with vgpu enabled ?  I had thought
>>    that this was done merely with the existing PCI passthrough
>>    configuration, but it now seems that somehow a second device model
>>    would have to be started.  libxl doesn't have code to do that.
>> 
> 
> AIUI if the setting of the increased limit is tied to provisioning a gvt-g 
> instance for a VM then I don't there needs to be extra information in the VM 
> config. These seems like the most sensible thing to do.

I don't understand this: For one, it's still unclear to me on what basis
it would be known that a given VM is a "gvt-g instance". And even if
that's indeed derivable from something, the uncertainty about a
workable upper bound on the number of WP ranges would still seem
to demand the value to be specifiable separately...

>> I now understand that these mmio ranges are created by the device
>> model.  Of course the device model needs to be able to create mmio
>> ranges for the guest.  And since they consume hypervisor resources,
>> the number of these must be limited (device models not necessarily
>> being trusted).
> 
> ...but I think there is still an open question as to whether the toolstack 
> is allowed to set that limit for a VM or not. IMO the toolstack should be 
> allowed to set that limit when creating a domain.

... as you indicate here.

Jan


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