From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta1.migadu.com (out-178.mta1.migadu.com [95.215.58.178]) (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 50AAF225DA for ; Fri, 25 Oct 2024 02:37:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729823868; cv=none; b=Gp0PbcMF3PCqLH9oSya2rf86SWDkD+flW8RDtn6gVoXN8/Pu9ArhfN76l96XHAAq5lCbxeepz9zsVCGyMlpieRT0ZaLC91SG6Q+Q6hL7zB3EZdVzNUZ3JiEgvO98mLdKeguG5nHlAAjY4ExE2WQq2CI6GkxkOb38hv5OB0ITl0M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729823868; c=relaxed/simple; bh=oCDqtzzq1WmrAd2KbGKue4dOh+1UHWTya7l1bGo/pAk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gl6n1dbVRdx9b/TIRL0W4kLo/VI0zCGiasT/q5j1Of+Rd7oz1wLs0GkekPrez6VxR5ThOMtiH9KQ23vvZtJRL9YxGwMQwbKVr97NzOUDzv38BLnwavHohNL+vOgKuSetefSYcVDeeOZ66FyMYzHenPmPjTWDo7yk9AG70Kh1RZw= 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=wPvXp6xq; arc=none smtp.client-ip=95.215.58.178 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="wPvXp6xq" Message-ID: <6f2c4bed-0b9c-48f7-886f-81e9df0155e7@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1729823862; 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=6YMGzBRFNqMsV1ec7cLGd4b9mG3UgxSE/vhPIc7vqCU=; b=wPvXp6xqcFCHWLK/3pZRHvT4yFi5jcHZYsY6Z6H8hj1LKp28A0GQGEiRz6rhB7pM0KpwB0 TUyceckG5rHFTVt92MknjFVA+Bjd551BOa0hqWTSmhu1P6RNIy3VJ7qgEAfYexIRMb479S H0xYumNvzZcpiWzheZdaQO9RqU1sysM= Date: Fri, 25 Oct 2024 10:37:35 +0800 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-US To: Alexei Starovoitov Cc: bpf , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Jiri Olsa , Eddy Z , 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: Leon Hwang In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 25/10/24 06:09, Alexei Starovoitov wrote: > On Mon, Oct 21, 2024 at 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 >> --- >> 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; > > I really don't like hacking flags into dst_reg. > We already abuse insn->off which is ugly too, > but at least we clean insns later after JIT. > > I'd rather live with this tail call inefficiency than abuse insns > fields further. > OK, let us use 'pseudo_call && tail_call_reachable' in x86 JIT to avoid touching 'insn->dst_reg'. Thanks, Leon > pw-bot: cr