On Wed, Oct 04, 2017 at 02:03:45PM +0200, Jesper Dangaard Brouer wrote:

The 'cpumap' is primary used as a backend map for XDP BPF helper
call bpf_redirect_map() and XDP_REDIRECT action, like 'devmap'.

This patch implement the main part of the map.  It is not connected to
the XDP redirect system yet, and no SKB allocation are done yet.

The main concern in this patch is to ensure the datapath can run
without any locking.  This adds complexity to the setup and tear-down
procedure, which assumptions are extra carefully documented in the
code comments.

V2:
 - make sure array isn't larger than NR_CPUS
 - make sure CPUs added is a valid possible CPU

V3: fix nitpicks from Jakub Kicinski [off-list ref]

Signed-off-by: Jesper Dangaard Brouer <redacted>

...

+static struct bpf_map *cpu_map_alloc(union bpf_attr *attr)
+{
+	struct bpf_cpu_map *cmap;
+	u64 cost;
+	int err;
+
+	/* check sanity of attributes */
+	if (attr->max_entries == 0 || attr->key_size != 4 ||
+	    attr->value_size != 4 || attr->map_flags & ~BPF_F_NUMA_NODE)
+		return ERR_PTR(-EINVAL);
+
+	cmap = kzalloc(sizeof(*cmap), GFP_USER);
+	if (!cmap)
+		return ERR_PTR(-ENOMEM);

just noticed that there is nothing here nor in DEVMAP/SOCKMAP
that prevents unpriv user to create them.
I'm not sure it was intentional for DEVMAP/SOCKMAP.
For CPUMAP I'd suggest to restrict it to root, since it
suppose to operate with XDP only which is root anyway.
Note, lpm and lru maps are cap_sys_admin only already.