[Qemu-devel] [PATCH] spapr: Don't use the "dual" interrupt controller mode with an old hypervisor

[Greg Kurz]

If KVM is too old to support XIVE native exploitation mode, we might end
up using the emulated XIVE after CAS. This is sub-optimal if KVM in-kernel
XICS is available, which is the case most of the time.

Also, an old KVM may not allow to destroy and re-create the KVM XICS, which
is precisely what "dual" does during machine reset. This causes QEMU to try
to switch to emulated XICS and to crash because RTAS call de-registration
isn't handled correctly. We could possibly fix that, but again we would
still end up with an emulated XICS or XIVE.

"dual" is definitely not a good choice with older KVMs. Internally force
XICS when we detect this.

Signed-off-by: Greg Kurz <address@hidden>
---
 hw/ppc/spapr_irq.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/hw/ppc/spapr_irq.c b/hw/ppc/spapr_irq.c
index 3156daf09381..d788bd662a7a 100644
--- a/hw/ppc/spapr_irq.c
+++ b/hw/ppc/spapr_irq.c
@@ -18,6 +18,7 @@
 #include "hw/ppc/xics_spapr.h"
 #include "cpu-models.h"
 #include "sysemu/kvm.h"
+#include "kvm_ppc.h"
 
 #include "trace.h"
 
@@ -668,6 +669,15 @@ static void spapr_irq_check(SpaprMachineState *spapr, 
Error **errp)
             return;
         }
     }
+
+    /*
+     * KVM may be too old to support XIVE, in which case we'd rather try
+     * to use the in-kernel XICS instead of the emulated XIVE.
+     */
+    if (kvm_enabled() && !kvmppc_has_cap_xive() &&
+        spapr->irq == &spapr_irq_dual) {
+        spapr->irq = &spapr_irq_xics;
+    }
 }
 
 /*