diff options
| -rw-r--r-- | hw/i386/xen/xen-mapcache.c | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/hw/i386/xen/xen-mapcache.c b/hw/i386/xen/xen-mapcache.c index 5b120ed44b..e82b7dcdd2 100644 --- a/hw/i386/xen/xen-mapcache.c +++ b/hw/i386/xen/xen-mapcache.c @@ -171,7 +171,20 @@ static void xen_remap_bucket(MapCacheEntry *entry, if (!(entry->flags & XEN_MAPCACHE_ENTRY_DUMMY)) { ram_block_notify_remove(entry->vaddr_base, 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); } |