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authorPeter Crosthwaite <peter.crosthwaite@xilinx.com>2015-12-14 17:36:21 +0000
committerPeter Maydell <peter.maydell@linaro.org>2016-01-08 13:32:55 +0000
commitae04887c393842c6016b09c746b4d7d6e7ee6996 (patch)
treee84cc30c31c49ee458dec5ce042a6b72d916d1e1
parent7d635a5b89f65f3e2089c3f19266fae1b209d234 (diff)
downloadqemu-arm-ae04887c393842c6016b09c746b4d7d6e7ee6996.tar.gz
memory: Add address_space_init_shareable()
This will either create a new AS or return a pointer to an already existing equivalent one, if we have already created an AS for the specified root memory region. The motivation is to reuse address spaces as much as possible. It's going to be quite common that bus masters out in device land have pointers to the same memory region for their mastering yet each will need to create its own address space. Let the memory API implement sharing for them. Aside from the perf optimisations, this should reduce the amount of redundant output on info mtree as well. Thee returned value will be malloced, but the malloc will be automatically freed when the AS runs out of refs. Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com> [PMM: dropped check for NULL root as unused; added doc-comment; squashed Peter C's reference-counting patch into this one; don't compare name string when deciding if we can share ASes; read as->malloced before the unref of as->root to avoid possible read-after-free if as->root was the owner of as] Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
-rw-r--r--include/exec/memory.h18
-rw-r--r--memory.c27
2 files changed, 45 insertions, 0 deletions
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 01f10049c1..c92734ae2b 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -241,6 +241,8 @@ struct AddressSpace {
struct rcu_head rcu;
char *name;
MemoryRegion *root;
+ int ref_count;
+ bool malloced;
/* Accessed via RCU. */
struct FlatView *current_map;
@@ -1189,6 +1191,22 @@ MemTxResult memory_region_dispatch_write(MemoryRegion *mr,
*/
void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name);
+/**
+ * address_space_init_shareable: return an address space for a memory region,
+ * creating it if it does not already exist
+ *
+ * @root: a #MemoryRegion that routes addresses for the address space
+ * @name: an address space name. The name is only used for debugging
+ * output.
+ *
+ * This function will return a pointer to an existing AddressSpace
+ * which was initialized with the specified MemoryRegion, or it will
+ * create and initialize one if it does not already exist. The ASes
+ * are reference-counted, so the memory will be freed automatically
+ * when the AddressSpace is destroyed via address_space_destroy.
+ */
+AddressSpace *address_space_init_shareable(MemoryRegion *root,
+ const char *name);
/**
* address_space_destroy: destroy an address space
diff --git a/memory.c b/memory.c
index 93bd8ed7bc..d2d0a92810 100644
--- a/memory.c
+++ b/memory.c
@@ -2124,7 +2124,9 @@ void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name)
{
memory_region_ref(root);
memory_region_transaction_begin();
+ as->ref_count = 1;
as->root = root;
+ as->malloced = false;
as->current_map = g_new(FlatView, 1);
flatview_init(as->current_map);
as->ioeventfd_nb = 0;
@@ -2139,6 +2141,7 @@ void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name)
static void do_address_space_destroy(AddressSpace *as)
{
MemoryListener *listener;
+ bool do_free = as->malloced;
address_space_destroy_dispatch(as);
@@ -2150,12 +2153,36 @@ static void do_address_space_destroy(AddressSpace *as)
g_free(as->name);
g_free(as->ioeventfds);
memory_region_unref(as->root);
+ if (do_free) {
+ g_free(as);
+ }
+}
+
+AddressSpace *address_space_init_shareable(MemoryRegion *root, const char *name)
+{
+ AddressSpace *as;
+
+ QTAILQ_FOREACH(as, &address_spaces, address_spaces_link) {
+ if (root == as->root && as->malloced) {
+ as->ref_count++;
+ return as;
+ }
+ }
+
+ as = g_malloc0(sizeof *as);
+ address_space_init(as, root, name);
+ as->malloced = true;
+ return as;
}
void address_space_destroy(AddressSpace *as)
{
MemoryRegion *root = as->root;
+ as->ref_count--;
+ if (as->ref_count) {
+ return;
+ }
/* Flush out anything from MemoryListeners listening in on this */
memory_region_transaction_begin();
as->root = NULL;