[RFC PATCH v2 6/6] bpf: Enable kprobe_multi feature if CONFIG_FPROBE is enabled

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Enable kprobe_multi feature if CONFIG_FPROBE is enabled. The pt_regs is
converted from ftrace_regs by ftrace_partial_regs(), thus some registers
may always returns 0. But it should be enough for function entry (access
arguments) and exit (access return value).

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 kernel/trace/bpf_trace.c |   22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 99c5f95360f9..0725272a3de2 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2460,7 +2460,7 @@ static int __init bpf_event_init(void)
 fs_initcall(bpf_event_init);
 #endif /* CONFIG_MODULES */
 
-#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+#ifdef CONFIG_FPROBE
 struct bpf_kprobe_multi_link {
 	struct bpf_link link;
 	struct fprobe fp;
@@ -2482,6 +2482,8 @@ struct user_syms {
 	char *buf;
 };
 
+static DEFINE_PER_CPU(struct pt_regs, bpf_kprobe_multi_pt_regs);
+
 static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32 cnt)
 {
 	unsigned long __user usymbol;
@@ -2623,13 +2625,14 @@ static u64 bpf_kprobe_multi_entry_ip(struct bpf_run_ctx *ctx)
 
 static int
 kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link,
-			   unsigned long entry_ip, struct pt_regs *regs)
+			   unsigned long entry_ip, struct ftrace_regs *fregs)
 {
 	struct bpf_kprobe_multi_run_ctx run_ctx = {
 		.link = link,
 		.entry_ip = entry_ip,
 	};
 	struct bpf_run_ctx *old_run_ctx;
+	struct pt_regs *regs;
 	int err;
 
 	if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1)) {
@@ -2639,6 +2642,7 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link,
 
 	migrate_disable();
 	rcu_read_lock();
+	regs = ftrace_partial_regs(fregs, this_cpu_ptr(&bpf_kprobe_multi_pt_regs));
 	old_run_ctx = bpf_set_run_ctx(&run_ctx.run_ctx);
 	err = bpf_prog_run(link->link.prog, regs);
 	bpf_reset_run_ctx(old_run_ctx);
@@ -2656,13 +2660,9 @@ kprobe_multi_link_handler(struct fprobe *fp, unsigned long fentry_ip,
 			  void *data)
 {
 	struct bpf_kprobe_multi_link *link;
-	struct pt_regs *regs = ftrace_get_regs(fregs);
-
-	if (!regs)
-		return 0;
 
 	link = container_of(fp, struct bpf_kprobe_multi_link, fp);
-	kprobe_multi_link_prog_run(link, get_entry_ip(fentry_ip), regs);
+	kprobe_multi_link_prog_run(link, get_entry_ip(fentry_ip), fregs);
 	return 0;
 }
 
@@ -2672,13 +2672,9 @@ kprobe_multi_link_exit_handler(struct fprobe *fp, unsigned long fentry_ip,
 			       void *data)
 {
 	struct bpf_kprobe_multi_link *link;
-	struct pt_regs *regs = ftrace_get_regs(fregs);
-
-	if (!regs)
-		return;
 
 	link = container_of(fp, struct bpf_kprobe_multi_link, fp);
-	kprobe_multi_link_prog_run(link, get_entry_ip(fentry_ip), regs);
+	kprobe_multi_link_prog_run(link, get_entry_ip(fentry_ip), fregs);
 }
 
 static int symbols_cmp_r(const void *a, const void *b, const void *priv)
@@ -2918,7 +2914,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 	kvfree(cookies);
 	return err;
 }
-#else /* !CONFIG_DYNAMIC_FTRACE_WITH_REGS */
+#else /* !CONFIG_FPROBE */
 int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 {
 	return -EOPNOTSUPP;