[Qemu-devel] [RFC PATCH 2/2] mem: prepare address_space listener rcu style

[Liu Ping Fan <qemulist@gmail.com>]

From: Liu Ping Fan <pingfank@linux.vnet.ibm.com>

Each address space listener has PhysPageMap *cur_map, *next_map,
the switch from cur_map to next_map complete the RCU style. The
mem_commit() do the switch, and it is against reader but AddressSpace's
lock or later RCU mechanism (around address_space_translate() ).

Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
---
 exec.c                         |   36 +++++++++++++++++++++++++++---------
 include/exec/memory-internal.h |   11 ++++++++++-
 2 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/exec.c b/exec.c
index bb4e540..e5871d6 100644
--- a/exec.c
+++ b/exec.c
@@ -186,24 +186,26 @@ static void phys_page_set(AddressSpaceDispatch *d,
                           hwaddr index, hwaddr nb,
                           uint16_t leaf)
 {
+    PhysPageMap *map = d->next_map;
     /* Wildly overreserve - it doesn't matter much. */
     phys_map_node_reserve(3 * P_L2_LEVELS);
 
-    phys_page_set_level(&d->phys_map, &index, &nb, leaf, P_L2_LEVELS - 1);
+    phys_page_set_level(&map->root, &index, &nb, leaf, P_L2_LEVELS - 1);
 }
 
 static PhysSection *phys_section_find(AddressSpaceDispatch *d,
                                       hwaddr index)
 {
-    PhysPageEntry lp = d->phys_map;
     PhysPageEntry *p;
-    PhysSection *phys_sections = cur_pgtbl->phys_sections;
-    Node *phys_map_nodes = cur_pgtbl->phys_map_nodes;
+    PhysPageEntry lp = d->cur_map->root;
+    PhysPageTable *pgtbl = d->cur_map->pgtbl;
+    PhysSection *phys_sections = pgtbl->phys_sections;
+    Node *phys_map_nodes = pgtbl->phys_map_nodes;
     int i;
 
     for (i = P_L2_LEVELS - 1; i >= 0 && !lp.is_leaf; i--) {
         if (lp.ptr == PHYS_MAP_NODE_NIL) {
-            return &phys_sections[cur_pgtbl->phys_section_unassigned];
+            return &phys_sections[pgtbl->phys_section_unassigned];
         }
         p = phys_map_nodes[lp.ptr];
         lp = p[(index >> (i * L2_BITS)) & (L2_SIZE - 1)];
@@ -234,7 +236,7 @@ MemoryRegionSection *address_space_translate(AddressSpace *as, hwaddr addr,
     IOMMUTLBEntry iotlb;
     MemoryRegionSection *section;
     hwaddr len = *plen;
-
+    PhysPageTable *pgtbl = cur_pgtbl;
     for (;;) {
         section = address_space_lookup_region(as, addr);
 
@@ -254,7 +256,7 @@ MemoryRegionSection *address_space_translate(AddressSpace *as, hwaddr addr,
                 | (addr & iotlb.addr_mask));
         len = MIN(len, (addr | iotlb.addr_mask) - addr + 1);
         if (!iotlb.perm[is_write]) {
-            section = &cur_pgtbl->phys_sections[cur_pgtbl->phys_section_unassigned].section;
+            section = &pgtbl->phys_sections[pgtbl->phys_section_unassigned].section;
             break;
         }
 
@@ -1703,7 +1705,21 @@ static void mem_begin(MemoryListener *listener)
 {
     AddressSpaceDispatch *d = container_of(listener, AddressSpaceDispatch, listener);
 
-    d->phys_map.ptr = PHYS_MAP_NODE_NIL;
+    d->next_map = g_new0(PhysPageMap, 1);
+    d->next_map->pgtbl = next_pgtbl;
+}
+
+static void mem_commit(MemoryListener *listener)
+{
+    AddressSpaceDispatch *d = container_of(listener, AddressSpaceDispatch, listener);
+    PhysPageMap *m = d->cur_map;
+
+    d->cur_map = d->next_map;
+    /* Fixme, Currently, we rely on biglock or address-space lock against
+    * reader. So here, we can safely drop it.
+    * After RCU, should change to call_rcu()
+    */
+    g_free(m);
 }
 
 static void core_begin(MemoryListener *listener)
@@ -1771,11 +1787,12 @@ void address_space_init_dispatch(AddressSpace *as)
 {
     AddressSpaceDispatch *d = g_new(AddressSpaceDispatch, 1);
 
-    d->phys_map  = (PhysPageEntry) { .ptr = PHYS_MAP_NODE_NIL, .is_leaf = 0 };
+    d->cur_map = g_new0(PhysPageMap, 1);
     d->listener = (MemoryListener) {
         .begin = mem_begin,
         .region_add = mem_add,
         .region_nop = mem_add,
+        .commit = mem_commit,
         .priority = 0,
     };
     as->dispatch = d;
@@ -1787,6 +1804,7 @@ void address_space_destroy_dispatch(AddressSpace *as)
     AddressSpaceDispatch *d = as->dispatch;
 
     memory_listener_unregister(&d->listener);
+    g_free(d->cur_map);
     g_free(d);
     as->dispatch = NULL;
 }
diff --git a/include/exec/memory-internal.h b/include/exec/memory-internal.h
index 1b156fd..0dfe260 100644
--- a/include/exec/memory-internal.h
+++ b/include/exec/memory-internal.h
@@ -30,13 +30,22 @@ struct PhysPageEntry {
     uint16_t ptr : 15;
 };
 
+struct PhysPageTable;
+typedef struct PhysPageMap PhysPageMap;
+
+struct PhysPageMap {
+    PhysPageEntry root;
+    struct PhysPageTable *pgtbl;
+};
+
 typedef struct AddressSpaceDispatch AddressSpaceDispatch;
 
 struct AddressSpaceDispatch {
     /* This is a multi-level map on the physical address space.
      * The bottom level has pointers to MemoryRegionSections.
      */
-    PhysPageEntry phys_map;
+    PhysPageMap *cur_map;
+    PhysPageMap *next_map;
     MemoryListener listener;
 };
 
-- 
1.7.4.4