From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 C867826A1C4; Fri, 10 Jul 2026 05:09:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783660182; cv=none; b=MTJrWNBHaKPAVCWPvagh62+vKscI83rEg81d6WDGLNQMRbLklH27u0TIGLST5xH1oWwizrqazAftsYTyIl9+ad0/NRsWGhQ3VxnmSzIeVmp0jctMnH1t91ruzke8gF4Kj1Ul8bfJkl8Jpv4fXjD7wQDdQQ0NNsHCgDDL4MbQ6xM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783660182; c=relaxed/simple; bh=0oASfdtSkBx2RepbUZpcih1U7xj0IUPhyZ9OhgcqHzc=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=ZY2puBteVHjwWb0PJB2G7l9dzYcjehekyXgQ4x30XC24E+uApmVMWVe2jG4BV2m5JcpznOLSG7ItrzTDCCt/mq74BmeO47njy8BuVWZ1YBzo8scfMypWwYauMGftKILYkR1Z43/G68EKcVKmjFLxQdkm1xReclTVw0Z0396N3us= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RV6c1iXa; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="RV6c1iXa" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CFD641F000E9; Fri, 10 Jul 2026 05:09:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783660181; bh=/gvB5qwbT78hXA6WigUj4DzknIHPDynctPCi9ezZArQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=RV6c1iXakob2plSYioZq0ZlQFxbU0si4E0zbzqFMhpsnIOL/qW84hVY3I/rBp5KA6 8jpgSJr3mGUxqYb/QpBzEOqPCMAm4KDqMvOFIY4umfyT/9gwFRbUIhZ1HWTJ3Dx5Ok s2KJUJqmWTd3MvL7/D5HJXiOseK9GWy8mtpjqoRhSXe1KQemCk3LuPvymovPU+SsIz 7l+sQk1Hg9fW2P4OvWMqa1I8el+LjzM0gEX2DAr0ZPhfWrVhdntU0er+Z1FYce0wRg m4EREBILvvVmtbsc4BdUA+1gmoBfAYJeTeHhFBq9sHZjQFKw7Xr/oNgEhcLmJsQ9GR IrpcOLcYdb/1A== Date: Fri, 10 Jul 2026 14:09:36 +0900 From: Masami Hiramatsu (Google) To: Pu Hu Cc: "ada.coupriediaz@arm.com" , "catalin.marinas@arm.com" , "davem@davemloft.net" , Hongyan Xia , Jiazi Li , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-trace-kernel@vger.kernel.org" , "naveen@kernel.org" , "will@kernel.org" , "yang@os.amperecomputing.com" Subject: Re: [RFC v2 2/3] arm64: kprobes: Allow reentering kprobes while single-stepping Message-Id: <20260710140936.8788416564452e490c71634c@kernel.org> In-Reply-To: <20260709142215.226872-3-hupu@transsion.com> References: <20260709142215.226872-1-hupu@transsion.com> <20260709142215.226872-3-hupu@transsion.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 9 Jul 2026 14:22:25 +0000 Pu Hu wrote: > From: Pu Hu > > A kprobe can be hit while another kprobe is in KPROBE_HIT_SS state. This > can happen when tracing or perf code runs from the debug exception path > while the first kprobe is preparing or executing its out-of-line > single-step instruction. > > Currently arm64 treats a kprobe hit in KPROBE_HIT_SS as unrecoverable, > the same as a hit in KPROBE_REENTER. This is too strict. A hit in > KPROBE_HIT_SS is still a one-level reentry and can be handled by saving > the current kprobe state and setting up single-step for the new probe, > just like reentry from KPROBE_HIT_ACTIVE or KPROBE_HIT_SSDONE. > > The truly unrecoverable case is hitting another kprobe while already in > KPROBE_REENTER, because the reentry save area has already been consumed. > > Move KPROBE_HIT_SS to the recoverable reentry cases and leave > KPROBE_REENTER as the unrecoverable nested reentry case. > > This mirrors the x86 fix in commit 6a5022a56ac3 > ("kprobes/x86: Allow to handle reentered kprobe on single-stepping"). > Hi, as Sashiko commented, we have to save the saved_irqflag to prev_kprobbe. https://sashiko.dev/#/patchset/20260709142215.226872-1-hupu%40transsion.com?part=2 Thank you, > Signed-off-by: Pu Hu > Signed-off-by: Hongyan Xia > --- > arch/arm64/kernel/probes/kprobes.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c > index 798e4b091d1a..2ca5916eca2f 100644 > --- a/arch/arm64/kernel/probes/kprobes.c > +++ b/arch/arm64/kernel/probes/kprobes.c > @@ -240,10 +240,16 @@ static int __kprobes reenter_kprobe(struct kprobe *p, > switch (kcb->kprobe_status) { > case KPROBE_HIT_SSDONE: > case KPROBE_HIT_ACTIVE: > + case KPROBE_HIT_SS: > + /* > + * A probe can be hit while another kprobe is preparing or > + * executing its XOL single-step instruction. This is still a > + * recoverable one-level reentry, so handle it in the same way as > + * reentry from KPROBE_HIT_ACTIVE or KPROBE_HIT_SSDONE. > + */ > kprobes_inc_nmissed_count(p); > setup_singlestep(p, regs, kcb, 1); > break; > - case KPROBE_HIT_SS: > case KPROBE_REENTER: > pr_warn("Failed to recover from reentered kprobes.\n"); > dump_kprobe(p); > -- > 2.43.0 > -- Masami Hiramatsu (Google)