From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 B2C2D20459A; Fri, 9 Jan 2026 13:47:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767966449; cv=none; b=ZOo3qUMFM6u+5JfjVXsVZ6dCuD9EjzLcb63DikZ1fQhYoEiCAOaZalpgoz+YtSVYBVDvZXy9Zp065dwG4NNXgzOJqN59zJD5RwnyGbeYVXGhxZPIJ3f3P+/dtGpKXzDkTaFMUJYfsKR7qSjYzN+OjaM4Ef2n5Xj6BOWnQjw/1Fk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767966449; c=relaxed/simple; bh=cEF2HlQxucHUoV1e6UadmpWp+jSEoVJADc0Y46qZqbs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=m+jw+7EVxjY99Mgn4ueQ4swdznzN5JJNtie0I+s0SwnBiJkCyPkFcDVkwuc1qyxfkp4A64HE/tR83D0iAcVwgENZ3oSODnsvZ3hPadQJ8bZvFVAOzEY8GZXoJPNvwx3noQBWiULz7UUE9tK7BHr5s+hycK0A8Do5ww7qLnGkDZY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=C1FWGrPc; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="C1FWGrPc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CB8A3C19422; Fri, 9 Jan 2026 13:47:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767966449; bh=cEF2HlQxucHUoV1e6UadmpWp+jSEoVJADc0Y46qZqbs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=C1FWGrPcQeROcGwnj7vSyZsZ1zoSFgaD4Ln4/ur1+e7jz2eTTP6zYm4hc6t69Rtx4 ZMmzuPPYsHpinghqDInHPL7rn5HeCDufgC5QuhRtbfMLhWFLcCU60gr6oeygzkIrDL 3jFoHuAyXCVfTLXcowVvzN7EuhmBtm8euqQh7RyfCox9zqcC/B5cvi9niLHeasjEIb QD6oexPs+n4lFjegd2rI/pWCvTT1Tedm5O83ZKR50AEKyofkAbTp3btKM6ZjDQrz9Q k7/CFJCmNVlIFPAnncs0QS5avgRg0WcLROqnnMZwJBKdvA8WGI9ZJFpKbjdQ9nuecr R94qzMn7rVI1g== Date: Fri, 9 Jan 2026 13:47:23 +0000 From: Will Deacon To: Jiri Olsa Cc: Masami Hiramatsu , Steven Rostedt , Mahe Tardy , 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 Subject: Re: [PATCHv2 bpf-next 1/2] arm64/ftrace,bpf: Fix partial regs after bpf_prog_run Message-ID: References: <20260109093454.389295-1-jolsa@kernel.org> 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-Disposition: inline In-Reply-To: <20260109093454.389295-1-jolsa@kernel.org> On Fri, Jan 09, 2026 at 10:34:53AM +0100, Jiri Olsa wrote: > Mahe reported issue with bpf_override_return helper not working when > executed from kprobe.multi bpf program on arm. > > The problem is 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. > > Fixing this by introducing and calling ftrace_partial_regs_update function > to propagate the values of changed registers (ip and stack). > > Reported-by: Mahe Tardy > Signed-off-by: Jiri Olsa > --- > v2 changes: > - moved ftrace_partial_regs_update to generic code [Will] > > include/linux/ftrace_regs.h | 25 +++++++++++++++++++++++++ > kernel/trace/bpf_trace.c | 1 + > 2 files changed, 26 insertions(+) > > diff --git a/include/linux/ftrace_regs.h b/include/linux/ftrace_regs.h > index 15627ceea9bc..f9a7c009cdae 100644 > --- a/include/linux/ftrace_regs.h > +++ b/include/linux/ftrace_regs.h > @@ -33,6 +33,31 @@ struct ftrace_regs; > #define ftrace_regs_get_frame_pointer(fregs) \ > frame_pointer(&arch_ftrace_regs(fregs)->regs) > > +static __always_inline void > +ftrace_partial_regs_update(const struct ftrace_regs *fregs, struct pt_regs *regs) { } > + > +#else > + > +/* > + * ftrace_partial_regs_update - update the original ftrace_regs from regs > + * @fregs: The ftrace_regs to update from @regs > + * @regs: The partial regs from ftrace_partial_regs() that was updated > + * > + * Some architectures have the partial regs living in the ftrace_regs > + * structure, whereas other architectures need to make a different copy > + * of the @regs. If a partial @regs is retrieved by ftrace_partial_regs() and > + * if the code using @regs updates a field (like the instruction pointer or > + * stack pointer) it may need to propagate that change to the original @fregs > + * it retrieved the partial @regs from. Use this function to guarantee that > + * update happens. > + */ > +static __always_inline void > +ftrace_partial_regs_update(const struct ftrace_regs *fregs, struct pt_regs *regs) > +{ > + ftrace_regs_set_instruction_pointer(fregs, instruction_pointer(regs)); > + ftrace_regs_set_return_value(fregs, regs_return_value(regs)); > +} I think the AI thingy is right about dropping the const qualifier here but overall I prefer this to the previous revisions. Thanks for sticking with it! Acked-by: Will Deacon Will