xics/spapr: Detect old KVM XICS on POWER9 hosts

Older KVMs on POWER9 don't support destroying/recreating a KVM XICS
device, which is required by 'dual' interrupt controller mode. This
causes QEMU to emit a warning when the guest is rebooted and to fall
back on XICS emulation:

qemu-system-ppc64: warning: kernel_irqchip allowed but unavailable:
 Error on KVM_CREATE_DEVICE for XICS: File exists

If kernel irqchip is required, QEMU will thus exit when the guest is
first rebooted. Failing QEMU this late may be a painful experience
for the user.

Detect that and exit at machine init instead.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <156044430517.125694.6207865998817342638.stgit@bahia.lab.toulouse-stg.fr.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 13 insertions, 0 deletions

diff --git a/hw/ppc/spapr_irq.c b/hw/ppc/spapr_irq.c
index dfb99f35ea..75654fc67a 100644
--- a/hw/ppc/spapr_irq.c
+++ b/hw/ppc/spapr_irq.c
@@ -669,6 +669,19 @@ static void spapr_irq_check(SpaprMachineState *spapr, Error **errp)
             return;
         }
     }
+
+    /*
+     * On a POWER9 host, some older KVM XICS devices cannot be destroyed and
+     * re-created. Detect that early to avoid QEMU to exit later when the
+     * guest reboots.
+     */
+    if (kvm_enabled() &&
+        spapr->irq == &spapr_irq_dual &&
+        machine_kernel_irqchip_required(machine) &&
+        xics_kvm_has_broken_disconnect(spapr)) {
+        error_setg(errp, "KVM is too old to support ic-mode=dual,kernel-irqchip=on");
+        return;
+    }
 }
 
 /*