[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-ppc] [PATCH v2 02/19] spapr: introduce a skeleton for the XIVE
Re: [Qemu-ppc] [PATCH v2 02/19] spapr: introduce a skeleton for the XIVE interrupt controller
Thu, 12 Apr 2018 15:10:31 +1000
On Wed, Jan 17, 2018 at 10:18:43AM +0100, Cédric Le Goater wrote:
> >>> Also, have we decided how the process of switching between XICS and
> >>> XIVE will work vs. CAS ?
> >> That's how it is described in the architecture. The current choice is
> >> to create both XICS and XIVE objects and choose at CAS which one to
> >> use. It relies today on the capability of the pseries machine to
> >> allocate IRQ numbers for both interrupt controller backends. These
> >> patches have been merged in QEMU.
> >> A change of interrupt mode results in a reset. The device tree is
> >> populated accordingly and the ICPs are switched for the model in
> >> use.
> > For KVM we need to only instanciate one of them though.
> How would we handle a guest rebooting on a kernel without XIVE support ?
> Are you suggesting to create the XICS or XIVE device in the CAS negotiation
> process ? So, the machine would not have any interrupt controller before
> CAS. That seems really late to me. grub uses the console for instance.
> I think it should prepare for both options, start in XIVE legacy mode,
> which is XICS, then possibly switch to XIVE exploitation mode.
I think for our first draft we should have XIVE and XICS based
platforms as separate machine types (or a machine option, I guess).
We do want to allow this to be autonegotiated, but I feel like
emphasising that at the beginning is causing unnatural design
decisions in the XIVE model itself.
> >>> And how that will interact with KVM ?
> >> I expect we will do the same, which is to create two KVM devices to
> >> be able to handle both interrupt controller backends depending on the
> >> mode negotiated by the guest.
> > That will be an ungodly mess, I'd rather we only instanciate the right
> > one.
> It's rather transparent currently in the emulated version. There are two
> sets of objects in QEMU, switching is done in CAS. KVM support should not
> change anything in that area.
> I expect the 'xive-kvm' object to get/set states for migration, just like
> for XICS and to setup the ESB+TIMA memory regions, which is new.
> >>> I was
> >>> thinking the kernel would implement a different KVM device type, ie
> >>> the "emulated XICS" would remain KVM_DEV_TYPE_XICS and XIVE would be
> >>> KVM_DEV_TYPE_XIVE.
> >> yes. it makes sense. The new device will have a lot in common with the
> >> KVM_DEV_TYPE_XICS using kvm_xive_ops.
> > Ben.
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_!
Description: PGP signature