Progress: * QEMU-420 [GICv4 emulation] - Tracked down and fixed a bug in our ITS emulation which would (intermittently?) result in a Linux guest reporting "irq 54: nobody cared" and hanging, because we were not correctly recalculating the highest priority pending interrupt when the guest acknowledged a pending LPI. This fix will go into 6.2. - Set up a test environment for GICv4 work -- because the major feature of GICv4 is support for directly injecting interrupts into a VM, the test setup needs to be nested virtualization, where an outer L1 guest runs on pure emulated QEMU, the inner L2 guest uses KVM (as provided by L1), and we pass a PCI device (emulated by QEMU) through from L1 to L2. I think I have this correctly set up now, but... - ...the L2 guest hangs because it apparently never sees an interrupt from the passed-through PCI device. This implies a bug in our current GICv3 emulation somewhere: need to track this down before starting in on GICv4 work. - Separately, I found through code inspection a bug where we do the wrong thing in the non-passthrough case when the L1 guest sets a virtual interrupt for the L2 guest in the GIC list registers and that interrupt has an ID > 1023 (ie it is an LPI). We got this wrong both for acknowledging and ending an interrupt, so the two bugs cancel each other out except that we don't set the vCPU priority and so the L2 guest might get an unexpected interrupt while it was servicing the LPI. Patches sent.

-- PMM