bpf: Define bpf_jit_alloc_exec_limit for riscv JIT

Expose the maximum amount of useable memory from the riscv JIT.
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Luke Nelson <luke.r.nels@gmail.com>
Acked-by: Björn Töpel <bjorn@kernel.org>
Link: https://lore.kernel.org/bpf/20211014142554.53120-2-lmb@cloudflare.com

arch/riscv/net/bpf_jit_core.c

@@ -166,6 +166,11 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 	return prog;
 }
 
+u64 bpf_jit_alloc_exec_limit(void)
+{
+	return BPF_JIT_REGION_SIZE;
+}
+
 void *bpf_jit_alloc_exec(unsigned long size)
 {
 	return __vmalloc_node_range(size, PAGE_SIZE, BPF_JIT_REGION_START,