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>

backends/hostmem.c

@@ -264,6 +264,16 @@ host_memory_backend_get_memory(HostMemoryBackend *backend, Error **errp)
     return memory_region_size(&backend->mr) ? &backend->mr : NULL;
 }
 
+void host_memory_backend_set_mapped(HostMemoryBackend *backend, bool mapped)
+{
+    backend->is_mapped = mapped;
+}
+
+bool host_memory_backend_is_mapped(HostMemoryBackend *backend)
+{
+    return backend->is_mapped;
+}
+
 static void
 host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
 {
@@ -341,10 +351,7 @@ host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
 static bool
 host_memory_backend_can_be_deleted(UserCreatable *uc, Error **errp)
 {
-    MemoryRegion *mr;
-
-    mr = host_memory_backend_get_memory(MEMORY_BACKEND(uc), errp);
-    if (memory_region_is_mapped(mr)) {
+    if (host_memory_backend_is_mapped(MEMORY_BACKEND(uc))) {
         return false;
     } else {
         return true;

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";
 

hw/misc/ivshmem.c

@@ -1008,10 +1008,7 @@ static const TypeInfo ivshmem_common_info = {
 static void ivshmem_check_memdev_is_busy(Object *obj, const char *name,
                                          Object *val, Error **errp)
 {
-    MemoryRegion *mr;
-
-    mr = host_memory_backend_get_memory(MEMORY_BACKEND(val), &error_abort);
-    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(errp, "can't use already busy memdev: %s", path);
         g_free(path);
@@ -1060,6 +1057,14 @@ static void ivshmem_plain_realize(PCIDevice *dev, Error **errp)
     }
 
     ivshmem_common_realize(dev, errp);
+    host_memory_backend_set_mapped(s->hostmem, true);
+}
+
+static void ivshmem_plain_exit(PCIDevice *pci_dev)
+{
+    IVShmemState *s = IVSHMEM_COMMON(pci_dev);
+
+    host_memory_backend_set_mapped(s->hostmem, false);
 }
 
 static void ivshmem_plain_class_init(ObjectClass *klass, void *data)
@@ -1068,6 +1073,7 @@ static void ivshmem_plain_class_init(ObjectClass *klass, void *data)
     PCIDeviceClass *k = PCI_DEVICE_CLASS(klass);
 
     k->realize = ivshmem_plain_realize;
+    k->exit = ivshmem_plain_exit;
     dc->props = ivshmem_plain_properties;
     dc->vmsd = &ivshmem_plain_vmsd;
 }

include/sysemu/hostmem.h

@@ -53,7 +53,7 @@ struct HostMemoryBackend {
     /* protected */
     uint64_t size;
     bool merge, dump;
-    bool prealloc, force_prealloc;
+    bool prealloc, force_prealloc, is_mapped;
     DECLARE_BITMAP(host_nodes, MAX_NODES + 1);
     HostMemPolicy policy;
 
@@ -63,4 +63,6 @@ struct HostMemoryBackend {
 MemoryRegion *host_memory_backend_get_memory(HostMemoryBackend *backend,
                                              Error **errp);
 
+void host_memory_backend_set_mapped(HostMemoryBackend *backend, bool mapped);
+bool host_memory_backend_is_mapped(HostMemoryBackend *backend);
 #endif