Re: [Xen-devel] Detecting PV drivers

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.04.13 at 19:00, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> On 04/04/13 17:30, Jon Ludlam wrote:
>> Hi,
>>
>> I'm trying find out the best way of detecting whether PV drivers have 
>> loaded in an HVM guest. For example, this is so we can decide whether or 
>> not to wait for a response from the guest when suspending.
>>
>> I think the best way of doing this is to find out whether the hypercall 
>> page has been populated or not, as this is the first thing that any PV 
>> drivers will have to do, but I don't know how to detect this, or even if 
>> this is possible - is there any way of finding this out?
> 
> Not currently as far as I can tell, but intercepting
> hvm_hypercall_page_initialise() and setting a boolean in struct domain
> would be easy.

But that doesn't in any way mean PV drivers are present. We have
a PV ticket lock implementation for HVM guests that necessarily also
sets up the hypercall page, yet this is in no way connected to the
presence of PV drivers.

> The better question would be how to get this information out of Xen.

And to me it's not obvious why looking at xenstore wouldn't be the
right thing - any frontend in connected state would indicate presence
of PV drivers, wouldn't it?

Jan



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