pc-dimm: add vhost slots limit check before commiting to hotplug

it allows safely cancel memory hotplug if vhost backend
doesn't support necessary amount of memory slots and prevents
QEMU crashing in vhost due to hitting vhost limit on amount
of supported memory ranges.
Signed-off-by: NIgor Mammedov <imammedo@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/mem/pc-dimm.c

@@ -25,6 +25,7 @@
 #include "sysemu/numa.h"
 #include "sysemu/kvm.h"
 #include "trace.h"
+#include "hw/virtio/vhost.h"
 
 typedef struct pc_dimms_capacity {
      uint64_t size;
@@ -96,6 +97,12 @@ void pc_dimm_memory_plug(DeviceState *dev, MemoryHotplugState *hpms,
         goto out;
     }
 
+    if (!vhost_has_free_slot()) {
+        error_setg(&local_err, "a used vhost backend has no free"
+                               " memory slots left");
+        goto out;
+    }
+
     memory_region_add_subregion(&hpms->mr, addr - hpms->base, mr);
     vmstate_register_ram(mr, dev);
     numa_set_mem_node_id(addr, memory_region_size(mr), dimm->node);