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, 30 insertions, 0 deletions

diff --git a/hw/intc/xics_kvm.c b/hw/intc/xics_kvm.c
index 5c4208f..c7f8f5e 100644
--- a/hw/intc/xics_kvm.c
+++ b/hw/intc/xics_kvm.c
@@ -452,3 +452,33 @@ void xics_kvm_disconnect(SpaprMachineState *spapr, Error **errp)
     /* Clear the presenter from the VCPUs */
     kvm_disable_icps();
 }
+
+/*
+ * This is a heuristic to detect older KVMs on POWER9 hosts that don't
+ * support destruction of a KVM XICS device while the VM is running.
+ * Required to start a spapr machine with ic-mode=dual,kernel-irqchip=on.
+ */
+bool xics_kvm_has_broken_disconnect(SpaprMachineState *spapr)
+{
+    int rc;
+
+    rc = kvm_create_device(kvm_state, KVM_DEV_TYPE_XICS, false);
+    if (rc < 0) {
+        /*
+         * The error is ignored on purpose. The KVM XICS setup code
+         * will catch it again anyway. The goal here is to see if
+         * close() actually destroys the device or not.
+         */
+        return false;
+    }
+
+    close(rc);
+
+    rc = kvm_create_device(kvm_state, KVM_DEV_TYPE_XICS, false);
+    if (rc >= 0) {
+        close(rc);
+        return false;
+    }
+
+    return errno == EEXIST;
+}