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. -- 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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