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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6EA85C38142 for ; Tue, 31 Jan 2023 07:12:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230183AbjAaHM2 (ORCPT ); Tue, 31 Jan 2023 02:12:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33974 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229503AbjAaHM0 (ORCPT ); Tue, 31 Jan 2023 02:12:26 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 98EE4302AF for ; Mon, 30 Jan 2023 23:12:25 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 3D43D61384 for ; Tue, 31 Jan 2023 07:12:25 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 319BEC433EF; Tue, 31 Jan 2023 07:12:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1675149144; bh=GLgjuhuoJia1KAR/5UGex45CJbUQqaV06MfhGq/cpgg=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=LG9+Z6uP0o6BTNazjYmtFoa+ZhTZHaq7InRd4D32TMcfZFvPAu/GFZXkeGKQpNfrh JnaiZsV6aEjsA1Y8PC4X61ZWGSBNdBXI1TN6GgTmX1KlLV8ibKByby1zXWkICShRWi qlOBtz4PQMbqWk8aTVDoFz+9X8NW1D0xCQc/tutAZK3KGnNIhcoJaPg9WB51YuYssi FDkNyDBfzlEuNMMXR1mTwc22cEbGezu+inYjgeQydjFYzn5kEW47Ec8U1fuODBL+xp 6Iy99il2z6Fkw1tzbs+DLo5k6o2AZL05J9wFElZNHTmDH4JrFL2MCXOvlPwd4J17tf URwpmqI2ACtSA== From: =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= To: Guo Ren , Mark Rutland Cc: "liaochang (A)" , palmer@dabbelt.com, paul.walmsley@sifive.com, mhiramat@kernel.org, conor.dooley@microchip.com, penberg@kernel.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Guo Ren Subject: Re: [PATCH] riscv: kprobe: Optimize kprobe with accurate atomicity In-Reply-To: References: <20230126161559.1467374-1-guoren@kernel.org> <0abbbdd4-6b85-9659-03ee-97c56a5b77c1@huawei.com> <87r0vc9h4g.fsf@all.your.base.are.belong.to.us> Date: Tue, 31 Jan 2023 08:12:22 +0100 Message-ID: <87a61z2n55.fsf@all.your.base.are.belong.to.us> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Guo Ren writes: > On Mon, Jan 30, 2023 at 11:49 PM Mark Rutland wrot= e: >> >> Hi Bjorn, >> >> On Mon, Jan 30, 2023 at 04:28:15PM +0100, Bj=C3=B6rn T=C3=B6pel wrote: >> > Guo Ren writes: >> > >> > >> In the serie of RISCV OPTPROBES [1], it patches a long-jump instruc= tions pair >> > >> AUIPC/JALR in kernel text, so in order to ensure other CPUs does no= t execute >> > >> in the instructions that will be modified, it is still need to stop= other CPUs >> > >> via patch_text API, or you have any better solution to achieve the = purpose? >> > > - The stop_machine is an expensive way all architectures should >> > > avoid, and you could keep that in your OPTPROBES implementation files >> > > with static functions. >> > > - The stop_machine couldn't work with PREEMPTION, so your >> > > implementation needs to work with !PREEMPTION. >> > >> > ...and stop_machine() with !PREEMPTION is broken as well, when you're >> > replacing multiple instructions (see Mark's post at [1]). The >> > stop_machine() dance might work when you're replacing *one* instructio= n, >> > not multiple as in the RISC-V case. I'll expand on this in a comment in >> > the OPTPROBES v6 series. >> >> Just to clarify, my comments in [1] were assuming that stop_machine() wa= s not >> used, in which case there is a problem with or without PREEMPTION. >> >> I believe that when using stop_machine(), the !PREEMPTION case is fine, = since >> stop_machine() schedules work rather than running work in IRQ context on= the >> back of an IPI, so no CPUs should be mid-sequnce during the patching, an= d it's >> not possible for there to be threads which are preempted mid-sequence. >> >> That all said, IIUC optprobes is going to disappear once fprobe is ready >> everywhere, so that might be moot. > The optprobes could be in the middle of a function, but fprobe must be > the entry of a function, right? > > Does your fprobe here mean: ? > > The Linux kernel configuration item CONFIG_FPROBE: > > prompt: Kernel Function Probe (fprobe) > type: bool > depends on: ( CONFIG_FUNCTION_TRACER ) && ( > CONFIG_DYNAMIC_FTRACE_WITH_REGS ) && ( CONFIG_HAVE_RETHOOK ) > defined in kernel/trace/Kconfig See the cover of [1]. It's about direct calls for BPF tracing (and more) on Arm, and you're completly right, that it's *not* related to optprobes at all. [1] https://lore.kernel.org/all/20221108220651.24492-1-revest@chromium.org/