diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index ca00daa2f5..7b9f92d51c 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -518,6 +518,27 @@ static int kvm_get_dirty_pages_log_range(MemoryRegionSection *section,
 
 #define ALIGN(x, y)  (((x)+(y)-1) & ~((y)-1))
 
+/* Allocate the dirty bitmap for a slot  */
+static void kvm_memslot_init_dirty_bitmap(KVMSlot *mem)
+{
+    /*
+     * XXX bad kernel interface alert
+     * For dirty bitmap, kernel allocates array of size aligned to
+     * bits-per-long.  But for case when the kernel is 64bits and
+     * the userspace is 32bits, userspace can't align to the same
+     * bits-per-long, since sizeof(long) is different between kernel
+     * and user space.  This way, userspace will provide buffer which
+     * may be 4 bytes less than the kernel will use, resulting in
+     * userspace memory corruption (which is not detectable by valgrind
+     * too, in most cases).
+     * So for now, let's align to 64 instead of HOST_LONG_BITS here, in
+     * a hope that sizeof(long) won't become >8 any time soon.
+     */
+    hwaddr bitmap_size = ALIGN(((mem->memory_size) >> TARGET_PAGE_BITS),
+                                        /*HOST_LONG_BITS*/ 64) / 8;
+    mem->dirty_bmap = g_malloc0(bitmap_size);
+}
+
 /**
  * kvm_physical_sync_dirty_bitmap - Sync dirty bitmap from kernel space
  *
@@ -550,23 +571,9 @@ static int kvm_physical_sync_dirty_bitmap(KVMMemoryListener *kml,
             goto out;
         }
 
-        /* XXX bad kernel interface alert
-         * For dirty bitmap, kernel allocates array of size aligned to
-         * bits-per-long.  But for case when the kernel is 64bits and
-         * the userspace is 32bits, userspace can't align to the same
-         * bits-per-long, since sizeof(long) is different between kernel
-         * and user space.  This way, userspace will provide buffer which
-         * may be 4 bytes less than the kernel will use, resulting in
-         * userspace memory corruption (which is not detectable by valgrind
-         * too, in most cases).
-         * So for now, let's align to 64 instead of HOST_LONG_BITS here, in
-         * a hope that sizeof(long) won't become >8 any time soon.
-         */
         if (!mem->dirty_bmap) {
-            hwaddr bitmap_size = ALIGN(((mem->memory_size) >> TARGET_PAGE_BITS),
-                                        /*HOST_LONG_BITS*/ 64) / 8;
             /* Allocate on the first log_sync, once and for all */
-            mem->dirty_bmap = g_malloc0(bitmap_size);
+            kvm_memslot_init_dirty_bitmap(mem);
         }
 
         d.dirty_bitmap = mem->dirty_bmap;
@@ -1067,6 +1074,13 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
         mem->ram = ram;
         mem->flags = kvm_mem_flags(mr);
 
+        if (mem->flags & KVM_MEM_LOG_DIRTY_PAGES) {
+            /*
+             * Reallocate the bmap; it means it doesn't disappear in
+             * middle of a migrate.
+             */
+            kvm_memslot_init_dirty_bitmap(mem);
+        }
         err = kvm_set_user_memory_region(kml, mem, true);
         if (err) {
             fprintf(stderr, "%s: error registering slot: %s\n", __func__,