Re: [net-next V7 PATCH 1/5] bpf: introduce new bpf cpu map type BPF_MAP_TYPE_CPUMAP

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]

V5:
 - Restrict map allocation to root / CAP_SYS_ADMIN
 - WARN_ON_ONCE if queue is not empty on tear-down
 - Return -EPERM on memlock limit instead of -ENOMEM
 - Error code in __cpu_map_entry_alloc() also handle ptr_ring_cleanup()
 - Moved cpu_map_enqueue() to next patch

V6: all notice by Daniel Borkmann
 - Fix err return code in cpu_map_alloc() introduced in V5
 - Move cpu_possible() check after max_entries boundary check
 - Forbid usage initially in check_map_func_compatibility()

V7:
 - Fix alloc error path spotted by Daniel Borkmann
 - Did stress test adding+removing CPUs from the map concurrently
 - Fixed refcnt issue on cpu_map_entry, kthread started too soon
 - Make sure packets are flushed during tear-down, involved use of
   rcu_barrier() and kthread_run only exit after queue is empty
 - Fix alloc error path in __cpu_map_entry_alloc() for ptr_ring

Signed-off-by: Jesper Dangaard Brouer <redacted>
---
 include/linux/bpf_types.h      |    1 
 include/uapi/linux/bpf.h       |    1 
 kernel/bpf/Makefile            |    1 
 kernel/bpf/cpumap.c            |  561 ++++++++++++++++++++++++++++++++++++++++
 kernel/bpf/syscall.c           |    8 -
 kernel/bpf/verifier.c          |    5 
 tools/include/uapi/linux/bpf.h |    1 
 7 files changed, 577 insertions(+), 1 deletion(-)
 create mode 100644 kernel/bpf/cpumap.c

diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
index 6f1a567667b8..814c1081a4a9 100644
--- a/include/linux/bpf_types.h
+++ b/include/linux/bpf_types.h

@@ -41,4 +41,5 @@ BPF_MAP_TYPE(BPF_MAP_TYPE_DEVMAP, dev_map_ops)
 #ifdef CONFIG_STREAM_PARSER
 BPF_MAP_TYPE(BPF_MAP_TYPE_SOCKMAP, sock_map_ops)
 #endif
+BPF_MAP_TYPE(BPF_MAP_TYPE_CPUMAP, cpu_map_ops)
 #endif

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 6db9e1d679cd..4303fb6c3817 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -112,6 +112,7 @@ enum bpf_map_type {
 	BPF_MAP_TYPE_HASH_OF_MAPS,
 	BPF_MAP_TYPE_DEVMAP,
 	BPF_MAP_TYPE_SOCKMAP,
+	BPF_MAP_TYPE_CPUMAP,
 };
 
 enum bpf_prog_type {

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 897daa005b23..dba0bd33a43c 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile

@@ -4,6 +4,7 @@ obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o
 obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o
 ifeq ($(CONFIG_NET),y)
 obj-$(CONFIG_BPF_SYSCALL) += devmap.o
+obj-$(CONFIG_BPF_SYSCALL) += cpumap.o
 ifeq ($(CONFIG_STREAM_PARSER),y)
 obj-$(CONFIG_BPF_SYSCALL) += sockmap.o
 endif

diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
new file mode 100644
index 000000000000..34db22afcca2
--- /dev/null
+++ b/kernel/bpf/cpumap.c

@@ -0,0 +1,561 @@
+/* bpf/cpumap.c
+ *
+ * Copyright (c) 2017 Jesper Dangaard Brouer, Red Hat Inc.
+ * Released under terms in GPL version 2.  See COPYING.
+ */
+
+/* The 'cpumap' is primary used as a backend map for XDP BPF helper