1 files changed, 18 insertions, 4 deletions

diff --git a/hw/i386/xen/xen-mapcache.c b/hw/i386/xen/xen-mapcache.c
index 5b120ed44b..bd47c3d672 100644
--- a/hw/i386/xen/xen-mapcache.c
+++ b/hw/i386/xen/xen-mapcache.c
@@ -169,9 +169,23 @@ static void xen_remap_bucket(MapCacheEntry *entry,
 
     if (entry->vaddr_base != NULL) {
         if (!(entry->flags & XEN_MAPCACHE_ENTRY_DUMMY)) {
-            ram_block_notify_remove(entry->vaddr_base, entry->size);
+            ram_block_notify_remove(entry->vaddr_base, entry->size,
+                                    entry->size);
         }
-        if (munmap(entry->vaddr_base, entry->size) != 0) {
+
+        /*
+         * If an entry is being replaced by another mapping and we're using
+         * MAP_FIXED flag for it - there is possibility of a race for vaddr
+         * address with another thread doing an mmap call itself
+         * (see man 2 mmap). To avoid that we skip explicit unmapping here
+         * and allow the kernel to destroy the previous mappings by replacing
+         * them in mmap call later.
+         *
+         * Non-identical replacements are not allowed therefore.
+         */
+        assert(!vaddr || (entry->vaddr_base == vaddr && entry->size == size));
+
+        if (!vaddr && munmap(entry->vaddr_base, entry->size) != 0) {
             perror("unmap fails");
             exit(-1);
         }
@@ -211,7 +225,7 @@ static void xen_remap_bucket(MapCacheEntry *entry,
     }
 
     if (!(entry->flags & XEN_MAPCACHE_ENTRY_DUMMY)) {
-        ram_block_notify_add(vaddr_base, size);
+        ram_block_notify_add(vaddr_base, size, size);
     }
 
     entry->vaddr_base = vaddr_base;
@@ -452,7 +466,7 @@ static void xen_invalidate_map_cache_entry_unlocked(uint8_t *buffer)
     }
 
     pentry->next = entry->next;
-    ram_block_notify_remove(entry->vaddr_base, entry->size);
+    ram_block_notify_remove(entry->vaddr_base, entry->size, entry->size);
     if (munmap(entry->vaddr_base, entry->size) != 0) {
         perror("unmap fails");
         exit(-1);