spapr: migration support for CAS-negotiated option vectors

With the additional of the OV5_HP_EVT option vector, we now have
certain functionality (namely, memory unplug) that checks at run-time
for whether or not the guest negotiated the option via CAS. Because
we don't currently migrate these negotiated values, we are unable
to unplug memory from a guest after it's been migrated until after
the guest is rebooted and CAS-negotiation is repeated.

This patch fixes this by adding CAS-negotiated options to the
migration stream. We do this using a subsection, since the
negotiated value of OV5_HP_EVT is the only option currently needed
to maintain proper functionality for a running guest.

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

hw/ppc/spapr.c

@@ -1267,6 +1267,68 @@ static bool version_before_3(void *opaque, int version_id)
     return version_id < 3;
 }
 
+static bool spapr_ov5_cas_needed(void *opaque)
+{
+    sPAPRMachineState *spapr = opaque;
+    sPAPROptionVector *ov5_mask = spapr_ovec_new();
+    sPAPROptionVector *ov5_legacy = spapr_ovec_new();
+    sPAPROptionVector *ov5_removed = spapr_ovec_new();
+    bool cas_needed;
+
+    /* Prior to the introduction of sPAPROptionVector, we had two option
+     * vectors we dealt with: OV5_FORM1_AFFINITY, and OV5_DRCONF_MEMORY.
+     * Both of these options encode machine topology into the device-tree
+     * in such a way that the now-booted OS should still be able to interact
+     * appropriately with QEMU regardless of what options were actually
+     * negotiatied on the source side.
+     *
+     * As such, we can avoid migrating the CAS-negotiated options if these
+     * are the only options available on the current machine/platform.
+     * Since these are the only options available for pseries-2.7 and
+     * earlier, this allows us to maintain old->new/new->old migration
+     * compatibility.
+     *
+     * For QEMU 2.8+, there are additional CAS-negotiatable options available
+     * via default pseries-2.8 machines and explicit command-line parameters.
+     * Some of these options, like OV5_HP_EVT, *do* require QEMU to be aware
+     * of the actual CAS-negotiated values to continue working properly. For
+     * example, availability of memory unplug depends on knowing whether
+     * OV5_HP_EVT was negotiated via CAS.
+     *
+     * Thus, for any cases where the set of available CAS-negotiatable
+     * options extends beyond OV5_FORM1_AFFINITY and OV5_DRCONF_MEMORY, we
+     * include the CAS-negotiated options in the migration stream.
+     */
+    spapr_ovec_set(ov5_mask, OV5_FORM1_AFFINITY);
+    spapr_ovec_set(ov5_mask, OV5_DRCONF_MEMORY);
+
+    /* spapr_ovec_diff returns true if bits were removed. we avoid using
+     * the mask itself since in the future it's possible "legacy" bits may be
+     * removed via machine options, which could generate a false positive
+     * that breaks migration.
+     */
+    spapr_ovec_intersect(ov5_legacy, spapr->ov5, ov5_mask);
+    cas_needed = spapr_ovec_diff(ov5_removed, spapr->ov5, ov5_legacy);
+
+    spapr_ovec_cleanup(ov5_mask);
+    spapr_ovec_cleanup(ov5_legacy);
+    spapr_ovec_cleanup(ov5_removed);
+
+    return cas_needed;
+}
+
+static const VMStateDescription vmstate_spapr_ov5_cas = {
+    .name = "spapr_option_vector_ov5_cas",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = spapr_ov5_cas_needed,
+    .fields = (VMStateField[]) {
+        VMSTATE_STRUCT_POINTER_V(ov5_cas, sPAPRMachineState, 1,
+                                 vmstate_spapr_ovec, sPAPROptionVector),
+        VMSTATE_END_OF_LIST()
+    },
+};
+
 static const VMStateDescription vmstate_spapr = {
     .name = "spapr",
     .version_id = 3,
@@ -1282,6 +1344,10 @@ static const VMStateDescription vmstate_spapr = {
         VMSTATE_PPC_TIMEBASE_V(tb, sPAPRMachineState, 2),
         VMSTATE_END_OF_LIST()
     },
+    .subsections = (const VMStateDescription*[]) {
+        &vmstate_spapr_ov5_cas,
+        NULL
+    }
 };
 
 static int htab_save_setup(QEMUFile *f, void *opaque)

hw/ppc/spapr_ovec.c

@@ -37,6 +37,17 @@
  */
 struct sPAPROptionVector {
     unsigned long *bitmap;
+    int32_t bitmap_size; /* only used for migration */
+};
+
+const VMStateDescription vmstate_spapr_ovec = {
+    .name = "spapr_option_vector",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .fields = (VMStateField[]) {
+        VMSTATE_BITMAP(bitmap, sPAPROptionVector, 1, bitmap_size),
+        VMSTATE_END_OF_LIST()
+    }
 };
 
 sPAPROptionVector *spapr_ovec_new(void)
@@ -45,6 +56,7 @@ sPAPROptionVector *spapr_ovec_new(void)
 
     ov = g_new0(sPAPROptionVector, 1);
     ov->bitmap = bitmap_new(OV_MAXBITS);
+    ov->bitmap_size = OV_MAXBITS;
 
     return ov;
 }

include/hw/ppc/spapr_ovec.h

@@ -37,6 +37,7 @@
 #define _SPAPR_OVEC_H
 
 #include "cpu.h"
+#include "migration/vmstate.h"
 
 typedef struct sPAPROptionVector sPAPROptionVector;
 
@@ -64,4 +65,7 @@ sPAPROptionVector *spapr_ovec_parse_vector(target_ulong table_addr, int vector);
 int spapr_ovec_populate_dt(void *fdt, int fdt_offset,
                            sPAPROptionVector *ov, const char *name);
 
+/* migration */
+extern const VMStateDescription vmstate_spapr_ovec;
+
 #endif /* !defined (_SPAPR_OVEC_H) */