Merge branch 'bpf-inline-bpf_kptr_xchg'

Hou Tao says:

====================
The motivation of inlining bpf_kptr_xchg() comes from the performance
profiling of bpf memory allocator benchmark [1]. The benchmark uses
bpf_kptr_xchg() to stash the allocated objects and to pop the stashed
objects for free. After inling bpf_kptr_xchg(), the performance for
object free on 8-CPUs VM increases about 2%~10%. However the performance
gain comes with costs: both the kasan and kcsan checks on the pointer
will be unavailable. Initially the inline is implemented in do_jit() for
x86-64 directly, but I think it will more portable to implement the
inline in verifier.

Patch #1 supports inlining bpf_kptr_xchg() helper and enables it on
x86-4. Patch #2 factors out a helper for newly-added test in patch #3.
Patch #3 tests whether the inlining of bpf_kptr_xchg() is expected.
Please see individual patches for more details. And comments are always
welcome.

Change Log:
v3:
  * rebased on bpf-next tree
  * patch 1 & 2: Add Rvb-by and Ack-by tags from Eduard
  * patch 3: use inline assembly and naked function instead of c code
             (suggested by Eduard)

v2: https://lore.kernel.org/bpf/20231223104042.1432300-1-houtao@huaweicloud.com/
  * rebased on bpf-next tree
  * drop patch #1 in v1 due to discussion in [2]
  * patch #1: add the motivation in the commit message, merge patch #1
              and #3 into the new patch in v2. (Daniel)
  * patch #2/#3: newly-added patch to test the inlining of
                 bpf_kptr_xchg() (Eduard)

v1: https://lore.kernel.org/bpf/95b8c2cd-44d5-5fe1-60b5-7e8218779566@huaweicloud.com/

[1]: https://lore.kernel.org/bpf/20231221141501.3588586-1-houtao@huaweicloud.com/
[2]: https://lore.kernel.org/bpf/fd94efb9-4a56-c982-dc2e-c66be5202cb7@huaweicloud.com/
====================

Link: https://lore.kernel.org/r/20240105104819.3916743-1-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

arch/x86/net/bpf_jit_comp.c

@@ -3242,3 +3242,8 @@ void bpf_arch_poke_desc_update(struct bpf_jit_poke_descriptor *poke,
 		BUG_ON(ret < 0);
 	}
 }
+
+bool bpf_jit_supports_ptr_xchg(void)
+{
+	return true;
+}

include/linux/filter.h

@@ -955,6 +955,7 @@ bool bpf_jit_supports_subprog_tailcalls(void);
 bool bpf_jit_supports_kfunc_call(void);
 bool bpf_jit_supports_far_kfunc_call(void);
 bool bpf_jit_supports_exceptions(void);
+bool bpf_jit_supports_ptr_xchg(void);
 void arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp), void *cookie);
 bool bpf_helper_changes_pkt_data(void *func);
 

kernel/bpf/core.c

@@ -2925,6 +2925,16 @@ bool __weak bpf_jit_supports_far_kfunc_call(void)
 	return false;
 }
 
+/* Return TRUE if the JIT backend satisfies the following two conditions:
+ * 1) JIT backend supports atomic_xchg() on pointer-sized words.
+ * 2) Under the specific arch, the implementation of xchg() is the same
+ *    as atomic_xchg() on pointer-sized words.
+ */
+bool __weak bpf_jit_supports_ptr_xchg(void)
+{
+	return false;
+}
+
 /* To execute LD_ABS/LD_IND instructions __bpf_prog_run() may call
  * skb_copy_bits(), so provide a weak definition of it for NET-less config.
  */

kernel/bpf/helpers.c

@@ -1414,6 +1414,7 @@ BPF_CALL_2(bpf_kptr_xchg, void *, map_value, void *, ptr)
 {
 	unsigned long *kptr = map_value;
 
+	/* This helper may be inlined by verifier. */
 	return xchg(kptr, (unsigned long)ptr);
 }
 

kernel/bpf/verifier.c

@@ -19809,6 +19809,23 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 			continue;
 		}
 
+		/* Implement bpf_kptr_xchg inline */
+		if (prog->jit_requested && BITS_PER_LONG == 64 &&
+		    insn->imm == BPF_FUNC_kptr_xchg &&
+		    bpf_jit_supports_ptr_xchg()) {
+			insn_buf[0] = BPF_MOV64_REG(BPF_REG_0, BPF_REG_2);
+			insn_buf[1] = BPF_ATOMIC_OP(BPF_DW, BPF_XCHG, BPF_REG_1, BPF_REG_0, 0);
+			cnt = 2;
+
+			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
+			if (!new_prog)
+				return -ENOMEM;
+
+			delta    += cnt - 1;
+			env->prog = prog = new_prog;
+			insn      = new_prog->insnsi + i + delta;
+			continue;
+		}
 patch_call_imm:
 		fn = env->ops->get_func_proto(insn->imm, env->prog);
 		/* all functions that have prototype and verifier allowed

tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c

@@ -626,50 +626,6 @@ static bool match_pattern(struct btf *btf, char *pattern, char *text, char *reg_
 	return false;
 }
 
-/* Request BPF program instructions after all rewrites are applied,
- * e.g. verifier.c:convert_ctx_access() is done.
- */
-static int get_xlated_program(int fd_prog, struct bpf_insn **buf, __u32 *cnt)
-{
-	struct bpf_prog_info info = {};
-	__u32 info_len = sizeof(info);
-	__u32 xlated_prog_len;
-	__u32 buf_element_size = sizeof(struct bpf_insn);
-
-	if (bpf_prog_get_info_by_fd(fd_prog, &info, &info_len)) {
-		perror("bpf_prog_get_info_by_fd failed");
-		return -1;
-	}
-
-	xlated_prog_len = info.xlated_prog_len;
-	if (xlated_prog_len % buf_element_size) {
-		printf("Program length %d is not multiple of %d\n",
-		       xlated_prog_len, buf_element_size);
-		return -1;
-	}
-
-	*cnt = xlated_prog_len / buf_element_size;
-	*buf = calloc(*cnt, buf_element_size);
-	if (!buf) {
-		perror("can't allocate xlated program buffer");
-		return -ENOMEM;
-	}
-
-	bzero(&info, sizeof(info));
-	info.xlated_prog_len = xlated_prog_len;
-	info.xlated_prog_insns = (__u64)(unsigned long)*buf;
-	if (bpf_prog_get_info_by_fd(fd_prog, &info, &info_len)) {
-		perror("second bpf_prog_get_info_by_fd failed");
-		goto out_free_buf;
-	}
-
-	return 0;
-
-out_free_buf:
-	free(*buf);
-	return -1;
-}
-
 static void print_insn(void *private_data, const char *fmt, ...)
 {
 	va_list args;

tools/testing/selftests/bpf/prog_tests/kptr_xchg_inline.c

@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2023. Huawei Technologies Co., Ltd */
+#include <test_progs.h>
+
+#include "linux/filter.h"
+#include "kptr_xchg_inline.skel.h"
+
+void test_kptr_xchg_inline(void)
+{
+	struct kptr_xchg_inline *skel;
+	struct bpf_insn *insn = NULL;
+	struct bpf_insn exp;
+	unsigned int cnt;
+	int err;
+
+#if !defined(__x86_64__)
+	test__skip();
+	return;
+#endif
+
+	skel = kptr_xchg_inline__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "open_load"))
+		return;
+
+	err = get_xlated_program(bpf_program__fd(skel->progs.kptr_xchg_inline), &insn, &cnt);
+	if (!ASSERT_OK(err, "prog insn"))
+		goto out;
+
+	/* The original instructions are:
+	 * r1 = map[id:xxx][0]+0
+	 * r2 = 0
+	 * call bpf_kptr_xchg#yyy
+	 *
+	 * call bpf_kptr_xchg#yyy will be inlined as:
+	 * r0 = r2
+	 * r0 = atomic64_xchg((u64 *)(r1 +0), r0)
+	 */
+	if (!ASSERT_GT(cnt, 5, "insn cnt"))
+		goto out;
+
+	exp = BPF_MOV64_REG(BPF_REG_0, BPF_REG_2);
+	if (!ASSERT_OK(memcmp(&insn[3], &exp, sizeof(exp)), "mov"))
+		goto out;
+
+	exp = BPF_ATOMIC_OP(BPF_DW, BPF_XCHG, BPF_REG_1, BPF_REG_0, 0);
+	if (!ASSERT_OK(memcmp(&insn[4], &exp, sizeof(exp)), "xchg"))
+		goto out;
+out:
+	free(insn);
+	kptr_xchg_inline__destroy(skel);
+}

tools/testing/selftests/bpf/progs/kptr_xchg_inline.c

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2023. Huawei Technologies Co., Ltd */
+#include <linux/types.h>
+#include <bpf/bpf_helpers.h>
+
+#include "bpf_experimental.h"
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+struct bin_data {
+	char blob[32];
+};
+
+#define private(name) SEC(".bss." #name) __hidden __attribute__((aligned(8)))
+private(kptr) struct bin_data __kptr * ptr;
+
+SEC("tc")
+__naked int kptr_xchg_inline(void)
+{
+	asm volatile (
+		"r1 = %[ptr] ll;"
+		"r2 = 0;"
+		"call %[bpf_kptr_xchg];"
+		"if r0 == 0 goto 1f;"
+		"r1 = r0;"
+		"r2 = 0;"
+		"call %[bpf_obj_drop_impl];"
+	"1:"
+		"r0 = 0;"
+		"exit;"
+		:
+		: __imm_addr(ptr),
+		  __imm(bpf_kptr_xchg),
+		  __imm(bpf_obj_drop_impl)
+		: __clobber_all
+	);
+}
+
+/* BTF FUNC records are not generated for kfuncs referenced
+ * from inline assembly. These records are necessary for
+ * libbpf to link the program. The function below is a hack
+ * to ensure that BTF FUNC records are generated.
+ */
+void __btf_root(void)
+{
+	bpf_obj_drop(NULL);
+}

tools/testing/selftests/bpf/test_verifier.c

@@ -1341,48 +1341,6 @@ static bool cmp_str_seq(const char *log, const char *exp)
 	return true;
 }
 
-static struct bpf_insn *get_xlated_program(int fd_prog, int *cnt)
-{
-	__u32 buf_element_size = sizeof(struct bpf_insn);
-	struct bpf_prog_info info = {};
-	__u32 info_len = sizeof(info);
-	__u32 xlated_prog_len;
-	struct bpf_insn *buf;
-
-	if (bpf_prog_get_info_by_fd(fd_prog, &info, &info_len)) {
-		perror("bpf_prog_get_info_by_fd failed");
-		return NULL;
-	}
-
-	xlated_prog_len = info.xlated_prog_len;
-	if (xlated_prog_len % buf_element_size) {
-		printf("Program length %d is not multiple of %d\n",
-		       xlated_prog_len, buf_element_size);
-		return NULL;
-	}
-
-	*cnt = xlated_prog_len / buf_element_size;
-	buf = calloc(*cnt, buf_element_size);
-	if (!buf) {
-		perror("can't allocate xlated program buffer");
-		return NULL;
-	}
-
-	bzero(&info, sizeof(info));
-	info.xlated_prog_len = xlated_prog_len;
-	info.xlated_prog_insns = (__u64)(unsigned long)buf;
-	if (bpf_prog_get_info_by_fd(fd_prog, &info, &info_len)) {
-		perror("second bpf_prog_get_info_by_fd failed");
-		goto out_free_buf;
-	}
-
-	return buf;
-
-out_free_buf:
-	free(buf);
-	return NULL;
-}
-
 static bool is_null_insn(struct bpf_insn *insn)
 {
 	struct bpf_insn null_insn = {};
@@ -1505,7 +1463,7 @@ static void print_insn(struct bpf_insn *buf, int cnt)
 static bool check_xlated_program(struct bpf_test *test, int fd_prog)
 {
 	struct bpf_insn *buf;
-	int cnt;
+	unsigned int cnt;
 	bool result = true;
 	bool check_expected = !is_null_insn(test->expected_insns);
 	bool check_unexpected = !is_null_insn(test->unexpected_insns);
@@ -1513,8 +1471,7 @@ static bool check_xlated_program(struct bpf_test *test, int fd_prog)
 	if (!check_expected && !check_unexpected)
 		goto out;
 
-	buf = get_xlated_program(fd_prog, &cnt);
-	if (!buf) {
+	if (get_xlated_program(fd_prog, &buf, &cnt)) {
 		printf("FAIL: can't get xlated program\n");
 		result = false;
 		goto out;

tools/testing/selftests/bpf/testing_helpers.c

@@ -387,3 +387,45 @@ int kern_sync_rcu(void)
 {
 	return syscall(__NR_membarrier, MEMBARRIER_CMD_SHARED, 0, 0);
 }
+
+int get_xlated_program(int fd_prog, struct bpf_insn **buf, __u32 *cnt)
+{
+	__u32 buf_element_size = sizeof(struct bpf_insn);
+	struct bpf_prog_info info = {};
+	__u32 info_len = sizeof(info);
+	__u32 xlated_prog_len;
+
+	if (bpf_prog_get_info_by_fd(fd_prog, &info, &info_len)) {
+		perror("bpf_prog_get_info_by_fd failed");
+		return -1;
+	}
+
+	xlated_prog_len = info.xlated_prog_len;
+	if (xlated_prog_len % buf_element_size) {
+		printf("Program length %u is not multiple of %u\n",
+		       xlated_prog_len, buf_element_size);
+		return -1;
+	}
+
+	*cnt = xlated_prog_len / buf_element_size;
+	*buf = calloc(*cnt, buf_element_size);
+	if (!buf) {
+		perror("can't allocate xlated program buffer");
+		return -ENOMEM;
+	}
+
+	bzero(&info, sizeof(info));
+	info.xlated_prog_len = xlated_prog_len;
+	info.xlated_prog_insns = (__u64)(unsigned long)*buf;
+	if (bpf_prog_get_info_by_fd(fd_prog, &info, &info_len)) {
+		perror("second bpf_prog_get_info_by_fd failed");
+		goto out_free_buf;
+	}
+
+	return 0;
+
+out_free_buf:
+	free(*buf);
+	*buf = NULL;
+	return -1;
+}

tools/testing/selftests/bpf/testing_helpers.h

@@ -46,4 +46,10 @@ static inline __u64 get_time_ns(void)
 	return (u64)t.tv_sec * 1000000000 + t.tv_nsec;
 }
 
+struct bpf_insn;
+/* Request BPF program instructions after all rewrites are applied,
+ * e.g. verifier.c:convert_ctx_access() is done.
+ */
+int get_xlated_program(int fd_prog, struct bpf_insn **buf, __u32 *cnt);
+
 #endif /* __TESTING_HELPERS_H */