[PATCH 00/19] KVM: PPC: Book3S HV: add XIVE native exploitation mode

[Cédric Le Goater]

On 2/6/19 2:18 AM, David Gibson wrote:
> On Wed, Feb 06, 2019 at 09:13:15AM +1100, Paul Mackerras wrote:
>> On Tue, Feb 05, 2019 at 12:31:28PM +0100, Cédric Le Goater wrote:
>>>>>> As for nesting, I suggest for the foreseeable future we stick to XICS
>>>>>> emulation in nested guests.
>>>>>
>>>>> ok. so no kernel_irqchip at all. hmm. 
>>>
>>> I was confused with what Paul calls 'XICS emulation'. It's not the QEMU
>>> XICS emulated device but the XICS-over-XIVE KVM device, the KVM XICS 
>>> device KVM uses when under a P9 processor. 
>>
>> Actually there are two separate implementations of XICS emulation in
>> KVM.  The first (older) one is almost entirely a software emulation
>> but does have some cases where it accesses an underlying XICS device
>> in order to make some things faster (IPIs and pass-through of a device
>> interrupt to a guest).  The other, newer one is the XICS-on-XIVE
>> emulation that Ben wrote, which uses the XIVE hardware pretty heavily.
>> My patch was about making the the older code work when there is no
>> XICS available to the host.
> 
> Ah, right.  To clarify my earlier statements in light of this:
> 
>  * We definitely want some sort of kernel-XICS available in a nested
>    guest.  AIUI, this is now accomplished, so, Yay!
> 
>  * Implementing the L2 XICS in terms of L1's PAPR-XIVE would be a
>    bonus, but it's a much lower priority.

Yes. In this case, the L1 KVM-HV should not advertise KVM_CAP_PPC_IRQ_XIVE
to QEMU which will restrict CAS to the XICS only interrupt mode.

C.