From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A35A033EA for ; Thu, 24 Oct 2024 17:01:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729789300; cv=none; b=oTiGK9ngRD4FV1yelAP4rQU+jaQEZPGCcAuNUPzbhXjWyDL+dqljONBsSzAwlNCB0xMZlRCLXqqXLk0qbQWwcz4xCBHTyZS27+yiQq62S/s4y2jecHybDZHEMfLvRwG+v5RcryQ2lLGG85IzYhDR6h7SNDf4w/rrxr0BYxS459s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729789300; c=relaxed/simple; bh=Bt7R8jlMbgsXTOq+Q5Jed+YefwuO5yK5e01yiMyGk+0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XmT4x7hYyGu3aI9K4H9Z27oZSKGBuYf1hZlWAjkDI3bnjPebE+WguN1mxQfeFSI4ZP4MIxWq/pCv2ZUYHCcMcfBHNGBd+My6z4JsP/JOspbTlCxaHL9MFLfWBRkifqGK1tfhDU9MjPwTlnUbfy2Fx1En3HyENrnZIvp6PTY8AX4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=rs2Y+AlW; arc=none smtp.client-ip=91.218.175.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="rs2Y+AlW" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1729789295; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=J0WIhlcaQ9lZWUk5krbyBEpDHAFxdxE3ELl5QfPYSzw=; b=rs2Y+AlWZEjgb4kmF7UMmLZXy4zgAlu+uT36JRrp9IetbS70jGMSDV5/HJVHrfWEpXIhQY 098FHEwOzM8UlJGqNPlyhvAdGNOn8qcxs5LnU3KKjDwjoKBPqpicuJiRRZ/erwkjmGn0+0 XNun7X9K3ug94FFdpVOjXNjs1z5hSto= Date: Thu, 24 Oct 2024 10:01:28 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next 1/2] bpf, x64: Propagate tailcall info only for tail_call_reachable subprogs Content-Language: en-GB To: Leon Hwang , bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, jolsa@kernel.org, eddyz87@gmail.com, kernel-patches-bot@fb.com References: <20241021133929.67782-1-leon.hwang@linux.dev> <20241021133929.67782-2-leon.hwang@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: <20241021133929.67782-2-leon.hwang@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 10/21/24 6:39 AM, Leon Hwang wrote: > In the x86_64 JIT, when calling a function, tailcall info is propagated if > the program is tail_call_reachable, regardless of whether the function is a > subprog, helper, or kfunc. However, this propagation is unnecessary for > not-tail_call_reachable subprogs, helpers, or kfuncs. > > The verifier can determine if a subprog is tail_call_reachable. Therefore, > it can be optimized to only propagate tailcall info when the callee is > subprog and the subprog is actually tail_call_reachable. > > Signed-off-by: Leon Hwang LGTM with a nit below. Acked-by: Yonghong Song > --- > arch/x86/net/bpf_jit_comp.c | 4 +++- > kernel/bpf/verifier.c | 6 ++++++ > 2 files changed, 9 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c > index 06b080b61aa57..6ad6886ecfc88 100644 > --- a/arch/x86/net/bpf_jit_comp.c > +++ b/arch/x86/net/bpf_jit_comp.c > @@ -2124,10 +2124,12 @@ st: if (is_imm8(insn->off)) > > /* call */ > case BPF_JMP | BPF_CALL: { > + bool pseudo_call = src_reg == BPF_PSEUDO_CALL; > + bool subprog_tail_call_reachable = dst_reg; > u8 *ip = image + addrs[i - 1]; > > func = (u8 *) __bpf_call_base + imm32; > - if (tail_call_reachable) { > + if (pseudo_call && subprog_tail_call_reachable) { > LOAD_TAIL_CALL_CNT_PTR(bpf_prog->aux->stack_depth); > ip += 7; > } > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index f514247ba8ba8..6e7e42c7bc7b1 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -19990,6 +19990,12 @@ static int jit_subprogs(struct bpf_verifier_env *env) > insn[0].imm = (u32)addr; > insn[1].imm = addr >> 32; > } > + > + if (bpf_pseudo_call(insn)) > + /* In the x86_64 JIT, tailcall information can only be > + * propagated if the subprog is tail_call_reachable. > + */ > + insn->dst_reg = env->subprog_info[subprog].tail_call_reachable; The comment can be simplied as /* Indicate whether callee is tail call reachable or not */ > } > > err = bpf_prog_alloc_jited_linfo(prog);