Re: [Qemu-devel] [PATCH v3 07/35] spapr/xive: introduce the XIVE Event Queues

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Apr 26, 2018 at 11:48:06AM +0200, Cédric Le Goater wrote:
> On 04/26/2018 09:25 AM, David Gibson wrote:
> > On Thu, Apr 19, 2018 at 02:43:03PM +0200, Cédric Le Goater wrote:
> >> The Event Queue Descriptor (EQD) table is an internal table of the
> >> XIVE routing sub-engine. It specifies on which Event Queue the event
> >> data should be posted when an exception occurs (later on pulled by the
> >> OS) and which Virtual Processor to notify.
> > 
> > Uhhh.. I thought the IVT said which queue and vp to notify, and the
> > EQD gave metadata for event queues.
> 
> yes. the above poorly written. The Event Queue Descriptor contains the
> guest address of the event queue in which the data is written. I will 
> rephrase.      
> 
> The IVT contains IVEs which indeed define for an IRQ which EQ to notify 
> and what data to push on the queue. 
>  
> >> The Event Queue is a much
> >> more complex structure but we start with a simple model for the sPAPR
> >> machine.
> >>
> >> There is one XiveEQ per priority and these are stored under the XIVE
> >> virtualization presenter (sPAPRXiveNVT). EQs are simply indexed with :
> >>
> >>        (server << 3) | (priority & 0x7)
> >>
> >> This is not in the XIVE architecture but as the EQ index is never
> >> exposed to the guest, in the hcalls nor in the device tree, we are
> >> free to use what fits best the current model.
> 
> This EQ indexing is important to notice because it will also show up 
> in KVM to build the IVE from the KVM irq state.

Ok, are you saying that while this combined EQ index will never appear
in guest <-> host interfaces, it might show up in qemu <-> KVM
interfaces?

> >> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> > 
> > Is the EQD actually modifiable by a guest?  Or are the settings of the
> > EQs fixed by PAPR?
> 
> The guest uses the H_INT_SET_QUEUE_CONFIG hcall to define the address
> of the event queue for a couple prio/server.

Ok, so the EQD can be modified by the guest.  In which case we need to
work out what object owns it, since it'll need to migrate it.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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