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=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 6D492C04EBF for ; Mon, 23 Sep 2019 11:49:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3676720882 for ; Mon, 23 Sep 2019 11:49:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="xjOY/yJA" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729727AbfIWLtc (ORCPT ); Mon, 23 Sep 2019 07:49:32 -0400 Received: from merlin.infradead.org ([205.233.59.134]:41554 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725793AbfIWLtb (ORCPT ); Mon, 23 Sep 2019 07:49:31 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=ph1WQsqjHm2MqFAqK+Rq1wUKmhEoeBwxc1DezgR1MvQ=; b=xjOY/yJAxhq3pjMxLi2rMPdo1 +G+szJYH/C+RE8i4eCh+peXajGrou/54xo/DrAFyJQHEumqz60ByBk8BjnbMQnMwXHFr8m1gmN7X8 g60ACSYpGBFCKbGMbUczJe1op8OLUaNboInW2OhqIqatD8eLrcJVGmjCsvFw09/AFjZ33E/OvsQy8 46/AVmIOgZvrmvPoCPMqUBTdb4LZTmGi+J8g2IpreKxNjfIgcrsHCWjQgey+n0iuuuueMxQG24cAp 9ga4ah4xiGBi0giLBwYxLDU8vB52cOokTqGNZdPweaavVQ7Z2RjpIsH7LMXvbijU/mNKOah3iAjPM onquEZ/VA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.2 #3 (Red Hat Linux)) id 1iCMqI-0002oW-EL; Mon, 23 Sep 2019 11:49:22 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id C1954301A7A; Mon, 23 Sep 2019 13:48:35 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id DB7D820C3E177; Mon, 23 Sep 2019 13:49:20 +0200 (CEST) Date: Mon, 23 Sep 2019 13:49:20 +0200 From: Peter Zijlstra To: Thomas Gleixner Cc: LKML , x86@kernel.org, Andy Lutomirski , Catalin Marinas , Will Deacon , Mark Rutland , Marc Zyngier , Paolo Bonzini , kvm@vger.kernel.org, linux-arch@vger.kernel.org, jgross@suse.com Subject: Re: [RFC patch 10/15] x86/entry: Move irq tracing to C code Message-ID: <20190923114920.GF2332@hirez.programming.kicks-ass.net> References: <20190919150314.054351477@linutronix.de> <20190919150809.446771597@linutronix.de> <20190923084718.GG2349@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 23, 2019 at 12:27:47PM +0200, Thomas Gleixner wrote: > On Mon, 23 Sep 2019, Peter Zijlstra wrote: > > > On Thu, Sep 19, 2019 at 05:03:24PM +0200, Thomas Gleixner wrote: > > > To prepare for converting the exit to usermode code to the generic version, > > > move the irqflags tracing into C code. > > > > > > Signed-off-by: Thomas Gleixner > > > --- > > > arch/x86/entry/common.c | 10 ++++++++++ > > > arch/x86/entry/entry_32.S | 11 +---------- > > > arch/x86/entry/entry_64.S | 10 ++-------- > > > arch/x86/entry/entry_64_compat.S | 21 --------------------- > > > 4 files changed, 13 insertions(+), 39 deletions(-) > > > > > > --- a/arch/x86/entry/common.c > > > +++ b/arch/x86/entry/common.c > > > @@ -102,6 +102,8 @@ static void exit_to_usermode_loop(struct > > > struct thread_info *ti = current_thread_info(); > > > u32 cached_flags; > > > > > > + trace_hardirqs_off(); > > > > Bah.. so this gets called from: > > > > - C code, with IRQs disabled > > - entry_64.S:error_exit > > - entry_32.S:resume_userspace > > > > The first obviously doesn't need this annotation, but this patch doesn't > > remove the TRACE_IRQS_OFF from entry_64.S and only the 32bit case is > > changed. > > > > Is that entry_64.S case an oversight, or do we need an extensive comment > > on this one? > > Lemme stare at that again. At some point I probably lost track in that maze. While walking the kids to school I wondered WTH we need to call TRACE_IRQS_OFF in the first place. If this is the return from exception path, interrupts had better be disabled already (in exception enter). For entry_64.S we have: - idtentry_part; which does TRACE_IRQS_OFF at the start and error_exit at the end. - xen_do_hypervisor_callback, xen_failsafe_callback -- which are confusing. So in the normal case, it appears we can simply do: diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index b7c3ea4cb19d..e9cf59ac554e 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -1368,8 +1368,6 @@ END(error_entry) ENTRY(error_exit) UNWIND_HINT_REGS - DISABLE_INTERRUPTS(CLBR_ANY) - TRACE_IRQS_OFF testb $3, CS(%rsp) jz retint_kernel jmp retint_user and all should be well. This leaves Xen... For entry_32.S it looks like nothing uses 'resume_userspace' so that ENTRY can go away. Which then leaves: * ret_from_intr: - common_spurious: TRACE_IRQS_OFF - common_interrupt: TRACE_IRQS_OFF - BUILD_INTERRUPT3: TRACE_IRQS_OFF - xen_do_upcall: ... * ret_from_exception: - xen_failsafe_callback: ... - common_exception_read_cr2: TRACE_IRQS_OFF - common_exception: TRACE_IRQS_OFF - int3: TRACE_IRQS_OFF Which again suggests: diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index f83ca5aa8b77..7a19e7413a8e 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -825,9 +825,6 @@ END(ret_from_fork) cmpl $USER_RPL, %eax jb restore_all_kernel # not returning to v8086 or userspace -ENTRY(resume_userspace) - DISABLE_INTERRUPTS(CLBR_ANY) - TRACE_IRQS_OFF movl %esp, %eax call prepare_exit_to_usermode jmp restore_all with the notable exception (oh teh pun!) being Xen... _again_. With these patchlets on, we'd want prepare_exit_to_usermode() to validate the IRQ state, but AFAICT it _should_ all just 'work' (famous last words). Cc Juergen because Xen