[Qemu-devel] [PATCH] spapr: Explicitly check machine support before using EVENT_CLASS_HOT_PLUG

[Greg Kurz <groug@kaod.org>]

Recent commit b8165118f52c "spapr: support memory unplug for qtest" broke
CPU hotplug tests for old machine types:

$ QTEST_QEMU_BINARY=ppc64-softmmu/qemu-system-ppc64 ./tests/cpu-plug-test -m=slow
/ppc64/cpu-plug/pseries-3.1/device-add/2x3x1&maxcpus=6: OK
/ppc64/cpu-plug/pseries-2.12-sxxm/device-add/2x3x1&maxcpus=6: OK
/ppc64/cpu-plug/pseries-3.0/device-add/2x3x1&maxcpus=6: OK
/ppc64/cpu-plug/pseries-2.10/device-add/2x3x1&maxcpus=6: OK
/ppc64/cpu-plug/pseries-2.11/device-add/2x3x1&maxcpus=6: OK
/ppc64/cpu-plug/pseries-2.12/device-add/2x3x1&maxcpus=6: OK
/ppc64/cpu-plug/pseries-2.9/device-add/2x3x1&maxcpus=6: OK
/ppc64/cpu-plug/pseries-2.7/device-add/2x3x1&maxcpus=6: **
ERROR:/home/thuth/devel/qemu/hw/ppc/spapr_events.c:313:rtas_event_log_to_source: assertion failed: (source->enabled)
Broken pipe
/home/thuth/devel/qemu/tests/libqtest.c:143: kill_qemu() detected QEMU death from signal 6 (Aborted) (core dumped)
Aborted (core dumped)

The rtas_event_log_to_source() function is supposed to return the event
source to be used for a given event type. In the case of hotplug, it first
tries EVENT_CLASS_HOT_PLUG and, if the guest doesn't support it, it falls
back to EVENT_CLASS_EPOW.

This works well for machine types that enable EVENT_CLASS_HOT_PLUG. For
older machine types, this happened to work because they don't set the
OV5_HP_EVT bit in spapr->ov5. CAS hence logically keeps the bit cleared
in spapr->ov5_cas and we avoid the assert.

As shown by commit b8165118f52c, the logic is fragile and we need a
bigger hammer to ensure that rtas_event_log_to_source() doesn't go
down the EVENT_CLASS_HOT_PLUG path with older machine types.

Signed-off-by: Greg Kurz <groug@kaod.org>
---
 hw/ppc/spapr_events.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/hw/ppc/spapr_events.c b/hw/ppc/spapr_events.c
index ab9a1f0063d5..1a09dab6857d 100644
--- a/hw/ppc/spapr_events.c
+++ b/hw/ppc/spapr_events.c
@@ -307,11 +307,13 @@ rtas_event_log_to_source(sPAPRMachineState *spapr, int log_type)
 
     switch (log_type) {
     case RTAS_LOG_TYPE_HOTPLUG:
-        source = spapr_event_sources_get_source(spapr->event_sources,
-                                                EVENT_CLASS_HOT_PLUG);
-        if (spapr_ovec_test(spapr->ov5_cas, OV5_HP_EVT)) {
-            g_assert(source->enabled);
-            break;
+        if (spapr->use_hotplug_event_source) {
+            source = spapr_event_sources_get_source(spapr->event_sources,
+                                                    EVENT_CLASS_HOT_PLUG);
+            if (spapr_ovec_test(spapr->ov5_cas, OV5_HP_EVT)) {
+                g_assert(source->enabled);
+                break;
+            }
         }
         /* fall back to epow for legacy hotplug interrupt source */
     case RTAS_LOG_TYPE_EPOW: