spapr_pci: Fix memory leak of vmstate_spapr_pci

When VM migrate VMState of spapr_pci, the field(msi_devs) of spapr_pci
having a flag of VMS_ALLOC need to allocate memory. If the src doesn't free
memory of msi_devs in SaveStateEntry of spapr_pci after QEMUFile save
VMState of spapr_pci, it may result in memory leak of msi_devs. We add the
post_save func to free memory, which prevents memory leak.

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Jinhao Gao <gaojinhao@huawei.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20201231061020.828-2-gaojinhao@huawei.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

hw/ppc/spapr_pci.c

@@ -2173,6 +2173,16 @@ static int spapr_pci_pre_save(void *opaque)
     return 0;
 }
 
+static int spapr_pci_post_save(void *opaque)
+{
+    SpaprPhbState *sphb = opaque;
+
+    g_free(sphb->msi_devs);
+    sphb->msi_devs = NULL;
+    sphb->msi_devs_num = 0;
+    return 0;
+}
+
 static int spapr_pci_post_load(void *opaque, int version_id)
 {
     SpaprPhbState *sphb = opaque;
@@ -2205,6 +2215,7 @@ static const VMStateDescription vmstate_spapr_pci = {
     .version_id = 2,
     .minimum_version_id = 2,
     .pre_save = spapr_pci_pre_save,
+    .post_save = spapr_pci_post_save,
     .post_load = spapr_pci_post_load,
     .fields = (VMStateField[]) {
         VMSTATE_UINT64_EQUAL(buid, SpaprPhbState, NULL),