bpf: Define bpf_jit_alloc_exec_limit for arm64 JIT

stable inclusion
from stable-5.10.80
commit a3564fb7b0bf11d941d57c87b0f38a656a997860
bugzilla: 185821 https://gitee.com/openeuler/kernel/issues/I4L7CG

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a3564fb7b0bf11d941d57c87b0f38a656a997860

--------------------------------

[ Upstream commit 5d63ae90 ]

Expose the maximum amount of useable memory from the arm64 JIT.
Signed-off-by: NLorenz Bauer <lmb@cloudflare.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211014142554.53120-3-lmb@cloudflare.comSigned-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Reviewed-by: NWeilong Chen <chenweilong@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/arm64/net/bpf_jit_comp.c

@@ -1134,6 +1134,11 @@ 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,