Merge branch 'Support kernel module ksym variables'

Andrii Nakryiko says:

====================

Add support for using kernel module global variables (__ksym externs in BPF
program). BPF verifier will now support ldimm64 with src_reg=BPF_PSEUDO_BTF_ID
and non-zero insn[1].imm field, specifying module BTF's FD. In such case,
module BTF object, similarly to BPF maps referenced from ldimm64 with
src_reg=BPF_PSEUDO_MAP_FD, will be recorded in bpf_progran's auxiliary data
and refcnt will be increased for both BTF object itself and its kernel module.
This makes sure kernel module won't be unloaded from under active attached BPF
program. These refcounts will be dropped when BPF program is unloaded.

New selftest validates all this is working as intended. bpf_testmod.ko is
extended with per-CPU variable. Selftests expects the latest pahole changes
(soon to be released as v1.20) to generate per-CPU variable BTF info for
kernel module.

v2->v3:
  - added comments, addressed feedack (Yonghong, Hao);
v1->v2:
  - fixed few compiler warnings, posted as separate pre-patches;
rfc->v1:
  - use sys_membarrier(MEMBARRIER_CMD_GLOBAL) (Alexei).

Cc: Hao Luo <haoluo@google.com>
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 31 insertions, 33 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/btf_map_in_map.c b/tools/testing/selftests/bpf/prog_tests/btf_map_in_map.c
index 76ebe4c250f1..eb90a6b8850d 100644
--- a/tools/testing/selftests/bpf/prog_tests/btf_map_in_map.c
+++ b/tools/testing/selftests/bpf/prog_tests/btf_map_in_map.c
@@ -20,39 +20,6 @@ static __u32 bpf_map_id(struct bpf_map *map)
 	return info.id;
 }
 
-/*
- * Trigger synchronize_rcu() in kernel.
- *
- * ARRAY_OF_MAPS/HASH_OF_MAPS lookup/update operations trigger synchronize_rcu()
- * if looking up an existing non-NULL element or updating the map with a valid
- * inner map FD. Use this fact to trigger synchronize_rcu(): create map-in-map,
- * create a trivial ARRAY map, update map-in-map with ARRAY inner map. Then
- * cleanup. At the end, at least one synchronize_rcu() would be called.
- */
-static int kern_sync_rcu(void)
-{
-	int inner_map_fd, outer_map_fd, err, zero = 0;
-
-	inner_map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, 4, 4, 1, 0);
-	if (CHECK(inner_map_fd < 0, "inner_map_create", "failed %d\n", -errno))
-		return -1;
-
-	outer_map_fd = bpf_create_map_in_map(BPF_MAP_TYPE_ARRAY_OF_MAPS, NULL,
-					     sizeof(int), inner_map_fd, 1, 0);
-	if (CHECK(outer_map_fd < 0, "outer_map_create", "failed %d\n", -errno)) {
-		close(inner_map_fd);
-		return -1;
-	}
-
-	err = bpf_map_update_elem(outer_map_fd, &zero, &inner_map_fd, 0);
-	if (err)
-		err = -errno;
-	CHECK(err, "outer_map_update", "failed %d\n", err);
-	close(inner_map_fd);
-	close(outer_map_fd);
-	return err;
-}
-
 static void test_lookup_update(void)
 {
 	int map1_fd, map2_fd, map3_fd, map4_fd, map5_fd, map1_id, map2_id;
diff --git a/tools/testing/selftests/bpf/prog_tests/ksyms_module.c b/tools/testing/selftests/bpf/prog_tests/ksyms_module.c
new file mode 100644
index 000000000000..4c232b456479
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/ksyms_module.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include <test_progs.h>
+#include <bpf/libbpf.h>
+#include <bpf/btf.h>
+#include "test_ksyms_module.skel.h"
+
+static int duration;
+
+void test_ksyms_module(void)
+{
+	struct test_ksyms_module* skel;
+	int err;
+
+	skel = test_ksyms_module__open_and_load();
+	if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
+		return;
+
+	err = test_ksyms_module__attach(skel);
+	if (CHECK(err, "skel_attach", "skeleton attach failed: %d\n", err))
+		goto cleanup;
+
+	usleep(1);
+
+	ASSERT_EQ(skel->bss->triggered, true, "triggered");
+	ASSERT_EQ(skel->bss->out_mod_ksym_global, 123, "global_ksym_val");
+
+cleanup:
+	test_ksyms_module__destroy(skel);
+}