[Qemu-devel] [PATCH] spapr/ppc: fix backward migration to QEMU 2.9

[Greg Kurz]

Commit c783b0012708 ("ppc: Rework CPU compatibility testing across
migration") added a subsection to the vmstate description of CPUs.
This subsection is sent when the CPU compat_pvr field is non-zero,
which is likely to happen after CAS negociation (since QEMU 2.9) or
even before CAS negociation if the user explicitely asked for compat
mode.

This breaks backward migration of existing pseries-2.9 machine types
since they don't know about this "compat" subsection:

qemu-system-ppc64: error while loading state for instance 0x0 of
 device 'cpu'

This patch reverts to the behavior of simply ignoring the PVR when
migrating older machines (ie, let the migration succeed if the user
is sure that the CPU on the destination is close enough to work).

Signed-off-by: Greg Kurz <address@hidden>
---
 hw/ppc/spapr.c              |    7 ++++++-
 target/ppc/cpu.h            |    1 +
 target/ppc/machine.c        |    2 +-
 target/ppc/translate_init.c |    2 ++
 4 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index d4d781876b27..265d49bbcd7f 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -3474,7 +3474,12 @@ DEFINE_SPAPR_MACHINE(2_10, "2.10", true);
  * pseries-2.9
  */
 #define SPAPR_COMPAT_2_9                                               \
-    HW_COMPAT_2_9
+    HW_COMPAT_2_9                                                      \
+    {                                                                  \
+        .driver = TYPE_POWERPC_CPU,                                    \
+        .property = "pre-2.10-migration",                              \
+        .value    = "on",                                              \
+    },                                                                 \
 
 static void spapr_machine_2_9_instance_options(MachineState *machine)
 {
diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h
index 09393e601fd9..6ee2a26a963d 100644
--- a/target/ppc/cpu.h
+++ b/target/ppc/cpu.h
@@ -1211,6 +1211,7 @@ struct PowerPCCPU {
     uint64_t mig_insns_flags;
     uint64_t mig_insns_flags2;
     uint32_t mig_nb_BATs;
+    bool pre_2_10_migration;
 };
 
 static inline PowerPCCPU *ppc_env_get_cpu(CPUPPCState *env)
diff --git a/target/ppc/machine.c b/target/ppc/machine.c
index a29aabe8f079..1b7aede579ea 100644
--- a/target/ppc/machine.c
+++ b/target/ppc/machine.c
@@ -608,7 +608,7 @@ static bool compat_needed(void *opaque)
     PowerPCCPU *cpu = opaque;
 
     assert(!(cpu->compat_pvr && !cpu->vhyp));
-    return (cpu->compat_pvr != 0);
+    return !cpu->pre_2_10_migration && cpu->compat_pvr != 0;
 }
 
 static const VMStateDescription vmstate_compat = {
diff --git a/target/ppc/translate_init.c b/target/ppc/translate_init.c
index 53aff5a7b734..783bf98217cc 100644
--- a/target/ppc/translate_init.c
+++ b/target/ppc/translate_init.c
@@ -10610,6 +10610,8 @@ static gchar *ppc_gdb_arch_name(CPUState *cs)
 
 static Property ppc_cpu_properties[] = {
     DEFINE_PROP_BOOL("pre-2.8-migration", PowerPCCPU, pre_2_8_migration, 
false),
+    DEFINE_PROP_BOOL("pre-2.10-migration", PowerPCCPU, pre_2_10_migration,
+                     false),
     DEFINE_PROP_END_OF_LIST(),
 };