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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,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 5EF42C04EBF for ; Mon, 23 Sep 2019 11:55:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 309F8205F4 for ; Mon, 23 Sep 2019 11:55:59 +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="oNVlammA" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730474AbfIWLz6 (ORCPT ); Mon, 23 Sep 2019 07:55:58 -0400 Received: from merlin.infradead.org ([205.233.59.134]:41600 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729656AbfIWLz6 (ORCPT ); Mon, 23 Sep 2019 07:55:58 -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=ZizFBvtwt2vz2u9q4gsPXlMp4iNJyEM3en3pt0PZaTg=; b=oNVlammAA0mezRMg90hLWDCXg Bw8JYsKy0YgSSLZEeZv8yq+CJlcasjWrKGNM5ouXxaIARaVg3ebsTk95TaUU5QrCokzzVWCMFlvRQ Vtz59wyOigu+YgucMO/LekcFXLCLVjzXbh038ca24Gam9r88BcWMN+GOFMN8SjlbCwDoDzQZjpWew yifS4BoJ7r83uDJAfDoS0qkTSYUhONJt+eTMsjfA377P3RSVzaKIOa9u2pcFDZNxV3I+9CdtEkKKj ZjXT4y1j1/Skr1tGJEerjqvi3kr8TTp9GrG76NB5D8foHfAK1mtm1QegyYqmplkeesX7p4CGjh1b/ 5UPj32ZjQ==; 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 1iCMwb-0002qz-9W; Mon, 23 Sep 2019 11:55:53 +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 DD873305E42; Mon, 23 Sep 2019 13:55:06 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 04C9820C3E176; Mon, 23 Sep 2019 13:55:51 +0200 (CEST) Date: Mon, 23 Sep 2019 13:55:51 +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: <20190923115551.GZ2386@hirez.programming.kicks-ass.net> References: <20190919150314.054351477@linutronix.de> <20190919150809.446771597@linutronix.de> <20190923084718.GG2349@hirez.programming.kicks-ass.net> <20190923114920.GF2332@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190923114920.GF2332@hirez.programming.kicks-ass.net> 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 01:49:20PM +0200, Peter Zijlstra wrote: > 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 Arrgh.. faults!! they do local_irq_enable() but never disable them again. Arguably those functions should be symmetric and restore IF when they muck with it instead of relying on the exit path fixing things up.