By default all guests are permitted to have up to 1024 maptrack frames, which on 64-bit means an 8k frame table. Yet except for driver domains guests normally don't make use of grant mappings. Defer allocating the table until a map track handle is first requested.
Signed-off-by: Jan Beulich <[email protected]> --- I continue to be unconvinced that it is a good idea to allow all DomU-s 1024 maptrack frames by default. While I'm still of the opinion that a hypervisor enforced upper bound is okay, I question this upper bound also getting used as the default value - this is perhaps okay for Dom0, but not elsewhere. --- a/xen/common/grant_table.c +++ b/xen/common/grant_table.c @@ -633,6 +633,34 @@ get_maptrack_handle( if ( likely(handle != INVALID_MAPTRACK_HANDLE) ) return handle; + if ( unlikely(!read_atomic(&lgt->maptrack)) ) + { + struct grant_mapping **maptrack = NULL; + + if ( lgt->max_maptrack_frames ) + maptrack = vzalloc(lgt->max_maptrack_frames * sizeof(*maptrack)); + + spin_lock(&lgt->maptrack_lock); + + if ( !lgt->maptrack ) + { + if ( !maptrack ) + { + spin_unlock(&lgt->maptrack_lock); + return INVALID_MAPTRACK_HANDLE; + } + + write_atomic(&lgt->maptrack, maptrack); + maptrack = NULL; + + radix_tree_init(&lgt->maptrack_tree); + } + + spin_unlock(&lgt->maptrack_lock); + + vfree(maptrack); + } + spin_lock(&lgt->maptrack_lock); /* @@ -1955,16 +1983,6 @@ int grant_table_init(struct domain *d, i if ( gt->active == NULL ) goto out; - /* Tracking of mapped foreign frames table */ - if ( gt->max_maptrack_frames ) - { - gt->maptrack = vzalloc(gt->max_maptrack_frames * sizeof(*gt->maptrack)); - if ( gt->maptrack == NULL ) - goto out; - - radix_tree_init(>->maptrack_tree); - } - /* Shared grant table. */ gt->shared_raw = xzalloc_array(void *, gt->max_grant_frames); if ( gt->shared_raw == NULL )
