[PATCH v3 bpf-next 2/3] bpf: Relax max_entries check for most of the inner map types

[Martin KaFai Lau]

Most of the maps do not use max_entries during verification time.
Thus, those map_meta_equal() do not need to enforce max_entries
when it is inserted as an inner map during runtime.  The max_entries
check is removed from the default implementation bpf_map_meta_equal().

The prog_array_map and xsk_map are exception.  Its map_gen_lookup
uses max_entries to generate inline lookup code.  Thus, they will
implement its own map_meta_equal() to enforce max_entries.
Since there are only two cases now, the max_entries check
is not refactored and stays in its own .c file.

Signed-off-by: Martin KaFai Lau <ka...@fb.com>
---
 kernel/bpf/arraymap.c   | 9 ++++++++-
 kernel/bpf/map_in_map.c | 3 +--
 net/xdp/xskmap.c        | 9 ++++++++-
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 40d1f7f94307..d851ebbcf302 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -487,6 +487,13 @@ static int array_map_mmap(struct bpf_map *map, struct 
vm_area_struct *vma)
                                   vma->vm_pgoff + pgoff);
 }
 
+static bool array_map_meta_equal(const struct bpf_map *meta0,
+                                const struct bpf_map *meta1)
+{
+       return meta0->max_entries == meta1->max_entries &&
+               bpf_map_meta_equal(meta0, meta1);
+}
+
 struct bpf_iter_seq_array_map_info {
        struct bpf_map *map;
        void *percpu_value_buf;
@@ -625,7 +632,7 @@ static const struct bpf_iter_seq_info iter_seq_info = {
 
 static int array_map_btf_id;
 const struct bpf_map_ops array_map_ops = {
-       .map_meta_equal = bpf_map_meta_equal,
+       .map_meta_equal = array_map_meta_equal,
        .map_alloc_check = array_map_alloc_check,
        .map_alloc = array_map_alloc,
        .map_free = array_map_free,
diff --git a/kernel/bpf/map_in_map.c b/kernel/bpf/map_in_map.c
index e97a22dd3232..39ab0b68cade 100644
--- a/kernel/bpf/map_in_map.c
+++ b/kernel/bpf/map_in_map.c
@@ -75,8 +75,7 @@ bool bpf_map_meta_equal(const struct bpf_map *meta0,
        return meta0->map_type == meta1->map_type &&
                meta0->key_size == meta1->key_size &&
                meta0->value_size == meta1->value_size &&
-               meta0->map_flags == meta1->map_flags &&
-               meta0->max_entries == meta1->max_entries;
+               meta0->map_flags == meta1->map_flags;
 }
 
 void *bpf_map_fd_get_ptr(struct bpf_map *map,
diff --git a/net/xdp/xskmap.c b/net/xdp/xskmap.c
index f45f29f04151..2a4fd6677155 100644
--- a/net/xdp/xskmap.c
+++ b/net/xdp/xskmap.c
@@ -254,9 +254,16 @@ void xsk_map_try_sock_delete(struct xsk_map *map, struct 
xdp_sock *xs,
        spin_unlock_bh(&map->lock);
 }
 
+static bool xsk_map_meta_equal(const struct bpf_map *meta0,
+                              const struct bpf_map *meta1)
+{
+       return meta0->max_entries == meta1->max_entries &&
+               bpf_map_meta_equal(meta0, meta1);
+}
+
 static int xsk_map_btf_id;
 const struct bpf_map_ops xsk_map_ops = {
-       .map_meta_equal = bpf_map_meta_equal,
+       .map_meta_equal = xsk_map_meta_equal,
        .map_alloc = xsk_map_alloc,
        .map_free = xsk_map_free,
        .map_get_next_key = xsk_map_get_next_key,
-- 
2.24.1