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, 4 deletions

diff --git a/backends/hostmem.c b/backends/hostmem.c
index 8dede4db2e..ac802570a8 100644
--- a/backends/hostmem.c
+++ b/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;