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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9D8D0C5479D for ; Mon, 9 Jan 2023 17:20:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235117AbjAIRUF (ORCPT ); Mon, 9 Jan 2023 12:20:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44494 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234812AbjAIRUC (ORCPT ); Mon, 9 Jan 2023 12:20:02 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 30A77175B0 for ; Mon, 9 Jan 2023 09:20:02 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E193FC14; Mon, 9 Jan 2023 09:20:43 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.37.246]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7C9DC3F587; Mon, 9 Jan 2023 09:19:59 -0800 (PST) Date: Mon, 9 Jan 2023 17:19:56 +0000 From: Mark Rutland To: guoren@kernel.org Cc: anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, conor.dooley@microchip.com, heiko@sntech.de, rostedt@goodmis.org, mhiramat@kernel.org, jolsa@redhat.com, bp@suse.de, jpoimboe@kernel.org, suagrfillet@gmail.com, andy.chiu@sifive.com, e.shatokhin@yadro.com, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH -next V6 1/7] riscv: ftrace: Fixup panic by disabling preemption Message-ID: References: <20230107133549.4192639-1-guoren@kernel.org> <20230107133549.4192639-2-guoren@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230107133549.4192639-2-guoren@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 07, 2023 at 08:35:43AM -0500, guoren@kernel.org wrote: > From: Andy Chiu > > In RISCV, we must use an AUIPC + JALR pair to encode an immediate, > forming a jump that jumps to an address over 4K. This may cause errors > if we want to enable kernel preemption and remove dependency from > patching code with stop_machine(). For example, if a task was switched > out on auipc. And, if we changed the ftrace function before it was > switched back, then it would jump to an address that has updated 11:0 > bits mixing with previous XLEN:12 part. > > p: patched area performed by dynamic ftrace > ftrace_prologue: > p| REG_S ra, -SZREG(sp) > p| auipc ra, 0x? ------------> preempted > ... > change ftrace function > ... > p| jalr -?(ra) <------------- switched back > p| REG_L ra, -SZREG(sp) > func: > xxx > ret What happens on SMP but not !PREEMPTION; can't a CPU be in the middle of this while you're patching the sequence? Do you have any guarantee as to the atomicity and ordering of instruction fetches? Thanks, Mark. > > Fixes: afc76b8b8011 ("riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT") > Signed-off-by: Andy Chiu > Signed-off-by: Guo Ren > --- > arch/riscv/Kconfig | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > index e2b656043abf..ee0d39b26794 100644 > --- a/arch/riscv/Kconfig > +++ b/arch/riscv/Kconfig > @@ -138,7 +138,7 @@ config RISCV > select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE > select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL > select HAVE_FUNCTION_GRAPH_TRACER > - select HAVE_FUNCTION_TRACER if !XIP_KERNEL > + select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION > > config ARCH_MMAP_RND_BITS_MIN > default 18 if 64BIT > -- > 2.36.1 >