[PATCH v8 4/6] memory: Add do_commit() and sanity check in address_space_to_flatview

[Chuang Xu]

In next patch, we wrap the vm_load into a whole mr transaction to speed
up vm_load. This brings a problem, old flatviews may be referenced
during the vm_load. vm_load contains far more memory updates than
referencing to a specific flatview, hence we introduce do_commit to
make sure address_space_to_flatview will return the newest flatview and
it should logically only be triggered in a few spots during vm_load.

Other than that, sanity check whether BQL or rcu is held before using
any flatview.

Signed-off-by: Chuang Xu <xuchuangxc...@bytedance.com>
---
 include/exec/memory.h | 23 +++++++++++++++++++++++
 softmmu/memory.c      |  5 +++++
 2 files changed, 28 insertions(+)

diff --git a/include/exec/memory.h b/include/exec/memory.h
index 6fa0b071f0..d6fd89db64 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -27,6 +27,7 @@
 #include "qemu/notify.h"
 #include "qom/object.h"
 #include "qemu/rcu.h"
+#include "qemu/main-loop.h"
 
 #define RAM_ADDR_INVALID (~(ram_addr_t)0)
 
@@ -1095,8 +1096,30 @@ struct FlatView {
     MemoryRegion *root;
 };
 
+bool memory_region_transaction_in_progress(void);
+
+void memory_region_transaction_do_commit(void);
+
 static inline FlatView *address_space_to_flatview(AddressSpace *as)
 {
+    if (qemu_mutex_iothread_locked()) {
+        /* We exclusively own the flatview now.. */
+        if (memory_region_transaction_in_progress()) {
+            /*
+             * Fetch the flatview within a transaction in-progress, it
+             * means current_map may not be the latest, we need to update
+             * immediately to make sure the caller won't see obsolete
+             * mapping.
+             */
+            memory_region_transaction_do_commit();
+        }
+
+        /* No further protection needed to access current_map */
+        return as->current_map;
+    }
+
+    /* Otherwise we must have had the RCU lock or something went wrong */
+    assert(rcu_read_is_locked());
     return qatomic_rcu_read(&as->current_map);
 }
 
diff --git a/softmmu/memory.c b/softmmu/memory.c
index 33ecc62ee9..6a8e8b4e71 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -1130,6 +1130,11 @@ void memory_region_transaction_commit(void)
     }
 }
 
+bool memory_region_transaction_in_progress(void)
+{
+    return memory_region_transaction_depth != 0;
+}
+
 static void memory_region_destructor_none(MemoryRegion *mr)
 {
 }
-- 
2.20.1