From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754825AbbCYRl4 (ORCPT ); Wed, 25 Mar 2015 13:41:56 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49958 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751344AbbCYRly (ORCPT ); Wed, 25 Mar 2015 13:41:54 -0400 Message-ID: <5512F339.8060209@redhat.com> Date: Wed, 25 Mar 2015 18:41:13 +0100 From: Denys Vlasenko User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Ingo Molnar CC: Linus Torvalds , Steven Rostedt , Borislav Petkov , "H. Peter Anvin" , Andy Lutomirski , Oleg Nesterov , Frederic Weisbecker , Alexei Starovoitov , Will Drewry , Kees Cook , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/4] x86/asm/entry/64: do not TRACE_IRQS fast SYSRET64 path References: <1427303896-24023-1-git-send-email-dvlasenk@redhat.com> <1427303896-24023-2-git-send-email-dvlasenk@redhat.com> <20150325172922.GA7321@gmail.com> In-Reply-To: <20150325172922.GA7321@gmail.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/25/2015 06:29 PM, Ingo Molnar wrote: > > * Denys Vlasenko wrote: > >> SYSRET code path has a small irq-off block. >> On this code path, TRACE_IRQS_ON can't be called right before interrupts >> are enabled for real, we can't clobber registers there. >> So current code does it earlier, in a safe place. >> >> But with this, TRACE_IRQS_OFF/ON frames just two fast instructions, >> which is ridiculous: now most of irq-off block is _outside_ of the framing. >> >> Do the same thing that we do on SYSCALL entry: do not track this irq-off block, >> it is very small to ever cause noticeable irq latency. >> >> Be careful: make sure that "jnz int_ret_from_sys_call_irqs_off" now does >> invoke TRACE_IRQS_OFF - move int_ret_from_sys_call_irqs_off label before >> TRACE_IRQS_OFF. > >> @@ -345,8 +346,8 @@ tracesys_phase2: >> */ >> GLOBAL(int_ret_from_sys_call) >> DISABLE_INTERRUPTS(CLBR_NONE) >> - TRACE_IRQS_OFF >> int_ret_from_sys_call_irqs_off: >> + TRACE_IRQS_OFF >> movl $_TIF_ALLWORK_MASK,%edi >> /* edi: mask to check */ > > This latter trick absolutely needs a comment, to keep future lockdep > developers from wondering about the mismatch and the weird label > placement ... Unsure how to format it. How about: DISABLE_INTERRUPTS(CLBR_NONE) int_ret_from_sys_call_irqs_off: /* jumps come here with irqs off */ TRACE_IRQS_OFF (In truth, there is only one jump as of now, but using pliral "jumps" if that would change)