From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) (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 863831F131C for ; Mon, 21 Oct 2024 17:49:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729532954; cv=none; b=sg8hFYUOKdunxGmjvqQKtdN4c1+JpD+VtgBuoPLYnbpH5yHABiZUA++5JNRPlPIAzr7jQTRyV3Ic4t3B63ezko8efOHWYYql5SuUSLNl12kJY3kuNXr0tyhrBvL/EXo9ZGVyn33t8LakOKwi3DGKXHm2wr+AmYd8Fm3xfhwGFNc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729532954; c=relaxed/simple; bh=xpGSAnis5mgPSfa+9LKXaeNm1q+E9Q7gPKFE6kePS3E=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tMtRQSQXAsttKSjMv27870taVmrXkZqbMjZzAv4dTPyNwXfkdBxNriFos+ZsKFsE55Wzh2j7jY/8dx4JKZKPvtz7ipoRT7b3gID/0kHQJlwBWeqASqLjVMmELt46Rt3lYqO8fYmAiNlKXXiGZpNEoa9N1Nz2/1/BGjMyPwWRG/M= 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=G+pR6ZMh; arc=none smtp.client-ip=91.218.175.181 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="G+pR6ZMh" Message-ID: <87faf17b-51aa-487f-8d49-bf297a64ffa6@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1729532949; 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=mL7LUy4tyvw9qW3qPJB6kcp5+G+BhZNJVvxCWEkLPCs=; b=G+pR6ZMhK16NyXg2Ro7n4pXeCr01wn0jTUJK6wPnJVr18n2cE5Xya4ZbSl/NlkxA8nFM2Y KZC6IOR9g9Udu8XEu1dWX/c8dDkOdkG0wEA3nMpV7ss90WFwdJbFsFioCDnOONdGZW8DR+ LkVC+7kRYlNN+hpX80Sxf9ZY9z4HzDs= Date: Mon, 21 Oct 2024 10:49:02 -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 > --- > 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) { Why we need subprog_tail_call_reachable? Does tail_call_reachable && psueudo_call work the same way? > 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; > } > > err = bpf_prog_alloc_jited_linfo(prog);