target-ppc: Allow eventual removal of old migration mistakes

Until very recently, the vmstate for ppc cpus included some poorly
thought out VMSTATE_EQUAL() components, that can easily break
migration compatibility, and did so between qemu-2.6 and later
versions.  A hack was recently added which fixes this migration
breakage, but it leaves the unhelpful cruft of these fields in the
migration stream.

This patch adds a new cpu property allowing these fields to be removed
from the stream entirely.  For the pseries-2.8 machine type - which
comes after the fix - and for all non-pseries machine types - which
aren't mature enough to care about cross-version migration - we remove
the fields from the stream.

For pseries-2.7 and earlier, The migration hack remains in place,
allowing backwards and forwards migration with the older machine
types.

This restricts the migration compatibility cruft to older machine
types, and at least opens the possibility of eventually deprecating
and removing it entirely.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>

1 files changed, 2 insertions, 1 deletions

diff --git a/target-ppc/cpu.h b/target-ppc/cpu.h
index 7798b2ec23..2a50c43689 100644
--- a/target-ppc/cpu.h
+++ b/target-ppc/cpu.h
@@ -1167,7 +1167,8 @@ struct PowerPCCPU {
     uint32_t max_compat;
     uint32_t cpu_version;
 
-    /* fields used only during migration for compatibility hacks */
+    /* Fields related to migration compatibility hacks */
+    bool pre_2_8_migration;
     target_ulong mig_msr_mask;
     uint64_t mig_insns_flags;
     uint64_t mig_insns_flags2;