Re: [Xen-devel] PVH questions

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

> Stefano Stabellini, le Wed 30 Jan 2013 14:28:39 +0000, a Ãcrit :
> > On Wed, 30 Jan 2013, Samuel Thibault wrote:
> > > A couple more questions:
> > > 
> > > - Does hvm_callback_vector flags designates routing events through
> > >   interrupt vector 0xf3?
> > 
> > XENFEAT_hvm_callback_vector determins the hypervisor capability, while
> > you need an HVMOP_set_param hypercall to set HVM_PARAM_CALLBACK_IRQ to 
> > enable it.
> 
> Ok, but I mean: does XENFEAT_hvm_callback_vector mean that
> HVM_PARAM_CALLBACK_IRQ can be set?

Yes.

> > >   And does hvm_callback_vector designates that fact?
> > 
> > PVH implies it
> 
> I know, but there's not "PVH" flag in the hypervisor capabilities,
> that's why I'm asking which flag advertises the capability.

Good point.

It is safe to assume that XENFEAT_hvm_callback_vector means a vector
injection via lapic, therefore Xen has to provide one.  However I
wouldn't assume anything about the presence of an IO-APIC and a PIT,
even though the current patch series would make them available.

In fact you shouldn't have to use them at all: no devices or interrupts
should go through the IO-APIC and you can use the PV timer for timer
interrupts.

I would argue that it might be a good idea not to emulate them at all
for PVH guests to avoid confusions.

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