LoongArch: BPF: No text_poke() for kernel text

The current implementation of bpf_arch_text_poke() requires 5 nops
at patch site which is not applicable for kernel/module functions.
Because LoongArch reserves ONLY 2 nops at the function entry. With
CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS=y, this can be done by ftrace
instead.

See the following commit for details:
  * commit b91e014 ("bpf: Make BPF trampoline use register_ftrace_direct() API")
  * commit 9cdc3b6 ("LoongArch: ftrace: Add direct call support")

Cc: [email protected]
Tested-by: Vincent Li <[email protected]>
Signed-off-by: Hengqi Chen <[email protected]>
Signed-off-by: Huacai Chen <[email protected]>

Author: chenhengqi

arch/loongarch/net/bpf_jit.c

@@ -1292,8 +1292,10 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
 	u32 old_insns[LOONGARCH_LONG_JUMP_NINSNS] = {[0 ... 4] = INSN_NOP};
 	u32 new_insns[LOONGARCH_LONG_JUMP_NINSNS] = {[0 ... 4] = INSN_NOP};
 
-	if (!is_kernel_text((unsigned long)ip) &&
-		!is_bpf_text_address((unsigned long)ip))
+	/* Only poking bpf text is supported. Since kernel function entry
+	 * is set up by ftrace, we rely on ftrace to poke kernel functions.
+	 */
+	if (!is_bpf_text_address((unsigned long)ip))
 		return -ENOTSUPP;
 
 	ret = emit_jump_or_nops(old_addr, ip, old_insns, is_call);