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 X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F0897C54FCB for ; Wed, 22 Apr 2020 20:17:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C2FC220767 for ; Wed, 22 Apr 2020 20:17:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726660AbgDVUR2 (ORCPT ); Wed, 22 Apr 2020 16:17:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:33810 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725779AbgDVUR2 (ORCPT ); Wed, 22 Apr 2020 16:17:28 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 409E02074B; Wed, 22 Apr 2020 20:17:27 +0000 (UTC) Date: Wed, 22 Apr 2020 16:17:25 -0400 From: Steven Rostedt To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, jpoimboe@redhat.com, x86@kernel.org, mhiramat@kernel.org, mbenes@suse.cz, jthierry@redhat.com, alexandre.chartre@oracle.com Subject: Re: [PATCH 3/3] x86/ftrace: Do not jump to direct code in created trampolines Message-ID: <20200422161725.667fa9aa@gandalf.local.home> In-Reply-To: <20200422200808.GX2483@worktop.programming.kicks-ass.net> References: <20200422162539.808362933@goodmis.org> <20200422162750.638839749@goodmis.org> <20200422200808.GX2483@worktop.programming.kicks-ass.net> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 22 Apr 2020 22:08:08 +0200 Peter Zijlstra wrote: > On Wed, Apr 22, 2020 at 12:25:42PM -0400, Steven Rostedt wrote: > > > @@ -367,6 +371,17 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size) > > if (WARN_ON(ret < 0)) > > goto fail; > > > > + /* No need to test direct calls on created trampolines */ > > + if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) { > > + /* NOP the jnz 1f; but make sure it's a 2 byte jnz */ > > + ip = trampoline + (jmp_offset - start_offset); > > + if (WARN_ON(*(char *)ip != 0x75)) > > + goto fail; > > + ret = probe_kernel_read(ip, ideal_nops[2], 2); > > Now you're just being silly, are you really, actually worried you can't > read ideal_nops[] ? Hah, that was more cut and paste. I guess a memcpy() would be more appropriate. > > > + if (ret < 0) > > + goto fail; > > + } > > + > > /* > > * The address of the ftrace_ops that is used for this trampoline > > * is stored at the end of the trampoline. This will be used to > > diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S > > index 0882758d165a..f72ef157feb3 100644 > > --- a/arch/x86/kernel/ftrace_64.S > > +++ b/arch/x86/kernel/ftrace_64.S > > @@ -241,6 +241,7 @@ SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL) > > */ > > movq ORIG_RAX(%rsp), %rax > > testq %rax, %rax > > +SYM_INNER_LABEL(ftrace_regs_caller_jmp, SYM_L_GLOBAL) > > jnz 1f > > > > I you worry about performance, it would make more sense to do something > like so: > > SYM_INNER_LABEL(ftrace_regs_caller_from, SYM_L_GLOBAL) > movq ORIG_RAX(%rsp), %rax > testq %rax, %rax > jnz 1f > SYM_INNER_LABEL(ftrace_regs_caller_to, SYM_L_GLOBAL) > > if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) { > ip = trampoline + (ftrace_regs_caller_from - start_offset); > ((u8[])ip)[0] = JMP8_INSN_OPCODE; > ((u8[])ip)[1] = ftrace_regs_caller_to - ftrace_regs_caller_from - JMP8_INSN_SIZE; > } > > Or nop the whole range, but it's like 10 bytes so I'm not sure that's > actually faster. That could work too. I'll play with that and actually do some benchmarks to see how much it affects things. Thanks! -- Steve