hostmem: detect host backend memory is being used properly

Currently, we use memory_region_is_mapped() to detect if the host
backend memory is being used. This works if the memory is directly
mapped into guest's address space, however, it is not true for
nvdimm as it uses aliased memory region to map the memory. This is
why this bug can happen:
   https://bugzilla.redhat.com/show_bug.cgi?id=1352769

Fix it by introduce a new filed, is_mapped, to HostMemoryBackend,
we set/clear this filed accordingly when the device link/unlink to
host backend memory

Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 11 insertions, 7 deletions

diff --git a/hw/mem/pc-dimm.c b/hw/mem/pc-dimm.c
index 249193a543..9e8dab0e89 100644
--- a/hw/mem/pc-dimm.c
+++ b/hw/mem/pc-dimm.c
@@ -369,14 +369,9 @@ static void pc_dimm_get_size(Object *obj, Visitor *v, const char *name,
 static void pc_dimm_check_memdev_is_busy(Object *obj, const char *name,
                                       Object *val, Error **errp)
 {
-    MemoryRegion *mr;
     Error *local_err = NULL;
 
-    mr = host_memory_backend_get_memory(MEMORY_BACKEND(val), &local_err);
-    if (local_err) {
-        goto out;
-    }
-    if (memory_region_is_mapped(mr)) {
+    if (host_memory_backend_is_mapped(MEMORY_BACKEND(val))) {
         char *path = object_get_canonical_path_component(val);
         error_setg(&local_err, "can't use already busy memdev: %s", path);
         g_free(path);
@@ -384,7 +379,6 @@ static void pc_dimm_check_memdev_is_busy(Object *obj, const char *name,
         qdev_prop_allow_set_link_before_realize(obj, name, val, &local_err);
     }
 
-out:
     error_propagate(errp, local_err);
 }
 
@@ -421,6 +415,15 @@ static void pc_dimm_realize(DeviceState *dev, Error **errp)
     if (ddc->realize) {
         ddc->realize(dimm, errp);
     }
+
+    host_memory_backend_set_mapped(dimm->hostmem, true);
+}
+
+static void pc_dimm_unrealize(DeviceState *dev, Error **errp)
+{
+    PCDIMMDevice *dimm = PC_DIMM(dev);
+
+    host_memory_backend_set_mapped(dimm->hostmem, false);
 }
 
 static MemoryRegion *pc_dimm_get_memory_region(PCDIMMDevice *dimm)
@@ -439,6 +442,7 @@ static void pc_dimm_class_init(ObjectClass *oc, void *data)
     PCDIMMDeviceClass *ddc = PC_DIMM_CLASS(oc);
 
     dc->realize = pc_dimm_realize;
+    dc->unrealize = pc_dimm_unrealize;
     dc->props = pc_dimm_properties;
     dc->desc = "DIMM memory module";