From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7CFACFA374B for ; Fri, 2 Jan 2026 14:52:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=mjh9c0cB/9fhw2icbvqjVGcrgDQlIY7+d70l/pRhBro=; b=LDHZFCWHnXA72rNK66DvhrnX+w z3XbRLJkq+QtHK2G/GGLC+/9nslZjEQPRxFMZZt6+lr8wtsBVEPywpQ9jEWHS43oU/uOAj2WBt54i BsmmZkJfsZ1tyI4ren2fCTZCDJ98rBoVXn5cvHS/U/5H1uRp05PuzS+fL3FuY2dxJLpFoMY+H+YOv P3foRAqsL451RmiINkJylOVHamHdAMl7klbP8Kba95AFdWdf4iPSqE+XG+CemkUBmOhLgaXlukgkl 3nRFmq6DDWZvc9j5R7FfIbce3QzMp4NUauUv8s07xPKOs1WyjcmmWatElE7mNnniPCo7C8KFyOwAo /UlySrVw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vbgW3-00000008O8C-0Wfj; Fri, 02 Jan 2026 14:52:35 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vbgW0-00000008O7Y-3xpZ for linux-arm-kernel@lists.infradead.org; Fri, 02 Jan 2026 14:52:34 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 41FD844140; Fri, 2 Jan 2026 14:52:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6B0BAC116B1; Fri, 2 Jan 2026 14:52:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767365552; bh=JQQ5LuFQIAK/IiQNjSgP3KNOzDhsqMGgsVNg6dB+StI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=n/vDziwnCwq1mltUECV7jiwGIjish4gYTwEefWcXF66tMsA+/3UW4qvnybkYaHTn4 EafDa92jcR6Yv1QDuywTsuuNfxdh4BffmTsun4ORuSyLUei3h3lcWX1fV/llAHpnMp pQPzEqJTTLMW4WrXXyHbohmeyTOxaRk0x0jnb7d843oNA1+pvsNglqzU6r2ir73KCc 7UA6OwtAlmxeqeTIjiqQhDJKUi9zvYM8H2MUAofDVvHXAjBguDSRc/XtuAqd9Oq9oT F+gsKUS66rDiU34l3iHRSwf8JRiYxsBPII2Jkw/yn+6aalLlvtI7nDPb2yfst/yRNR FwSGKYRmj32bw== Date: Fri, 2 Jan 2026 14:52:25 +0000 From: Will Deacon To: Jiri Olsa Cc: Masami Hiramatsu , Steven Rostedt , Peter Zijlstra , bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, Yonghong Song , Song Liu , Andrii Nakryiko , Mark Rutland , Mahe Tardy Subject: Re: [BUG/RFC 1/2] arm64/ftrace,bpf: Fix partial regs after bpf_prog_run Message-ID: References: <20251105125924.365205-1-jolsa@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251105125924.365205-1-jolsa@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260102_065233_005100_19E47551 X-CRM114-Status: GOOD ( 24.60 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Nov 05, 2025 at 01:59:23PM +0100, Jiri Olsa wrote: > hi, > Mahe reported issue with bpf_override_return helper not working > when executed from kprobe.multi bpf program on arm. > > The problem seems to be that on arm we use alternate storage for > pt_regs object that is passed to bpf_prog_run and if any register > is changed (which is the case of bpf_override_return) it's not > propagated back to actual pt_regs object. > > The change below seems to fix the issue, but I have no idea if > that's proper fix for arm, thoughts? > > I'm attaching selftest to actually test bpf_override_return helper > functionality, because currently we only test that we are able to > attach a program with it, but not the override itself. > > thanks, > jirka > > > --- > arch/arm64/include/asm/ftrace.h | 11 +++++++++++ > include/linux/ftrace.h | 3 +++ > kernel/trace/bpf_trace.c | 1 + > 3 files changed, 15 insertions(+) > > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h > index ba7cf7fec5e9..ad6cf587885c 100644 > --- a/arch/arm64/include/asm/ftrace.h > +++ b/arch/arm64/include/asm/ftrace.h > @@ -157,6 +157,17 @@ ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs) > return regs; > } > > +static __always_inline void > +ftrace_partial_regs_fix(const struct ftrace_regs *fregs, struct pt_regs *regs) > +{ > + struct __arch_ftrace_regs *afregs = arch_ftrace_regs(fregs); > + > + if (afregs->pc != regs->pc) { > + afregs->pc = regs->pc; > + afregs->regs[0] = regs->regs[0]; > + } > +} This looks a bit grotty to me and presumably other architectures would need similar treatement. Wouldn't it be cleaner to reuse the existing API instead? For example, by calling ftrace_regs_set_instruction_pointer() and ftrace_regs_set_return_value() to update the relevant registers from the core code? Will