[Qemu-devel] [PATCH] spapr: Correct compatibility mode setting for hotplugged CPUs

[David Gibson <david@gibson.dropbear.id.au>]

Currently the pseries machine sets the compatibility mode for the
guest's cpus in two places: 1) at machine reset and 2) after CAS
negotiation.

This means that if we set or negotiate a compatiblity mode, then
hotplug a cpu, the hotplugged cpu doesn't get the right mode set and
will incorrectly have the full native features.

To correct this, we set the compatibility mode on a cpu when it is
brought online with the 'start-cpu' RTAS call.  Given that we no
longer need to set the compatibility mode on all CPUs at machine
reset, so we change that to only set the mode for the boot cpu.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 hw/ppc/spapr.c      | 2 +-
 hw/ppc/spapr_rtas.c | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index e22888ba06..d1acfe8858 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -1510,7 +1510,7 @@ static void spapr_machine_reset(void)
         spapr_ovec_cleanup(spapr->ov5_cas);
         spapr->ov5_cas = spapr_ovec_new();
 
-        ppc_set_compat_all(spapr->max_compat_pvr, &error_fatal);
+        ppc_set_compat(first_ppc_cpu, spapr->max_compat_pvr, &error_fatal);
     }
 
     fdt = spapr_build_fdt(spapr, rtas_addr, spapr->rtas_size);
diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
index 4bb939d3d1..2ed00548c1 100644
--- a/hw/ppc/spapr_rtas.c
+++ b/hw/ppc/spapr_rtas.c
@@ -163,6 +163,7 @@ static void rtas_start_cpu(PowerPCCPU *cpu_, sPAPRMachineState *spapr,
         CPUState *cs = CPU(cpu);
         CPUPPCState *env = &cpu->env;
         PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
+        Error *local_err = NULL;
 
         if (!cs->halted) {
             rtas_st(rets, 0, RTAS_OUT_HW_ERROR);
@@ -174,6 +175,13 @@ static void rtas_start_cpu(PowerPCCPU *cpu_, sPAPRMachineState *spapr,
          * new cpu enters */
         kvm_cpu_synchronize_state(cs);
 
+        /* Set compatibility mode to match existing cpus */
+        ppc_set_compat(cpu, POWERPC_CPU(first_cpu)->compat_pvr, &local_err);
+        if (local_err) {
+            rtas_st(rets, 0, RTAS_OUT_HW_ERROR);
+            return;
+        }
+
         env->msr = (1ULL << MSR_SF) | (1ULL << MSR_ME);
 
         /* Enable Power-saving mode Exit Cause exceptions for the new CPU */
-- 
2.14.3