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=-4.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 9502DC4CECF for ; Mon, 23 Sep 2019 17:24:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 62A1D20820 for ; Mon, 23 Sep 2019 17:24:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1569259457; bh=DzycgKHCi19mMx4cgC/hY8TzO4MUiU13rQpq2YThoZE=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=DgkeZBIPXc/aVMyXRxMGcBMfMDDxT7g2766gxix99O8diYNBlvnbjLcr0Ew8Lyvht mITOA43bxltfGscrC4qQVc/wOLc+oLxBX4nNIxIc5LcH5pnFQSpxs9T0uowPkIB/Jg raHUI0f0OdQKoeUdbjKSNSDSe+BGMjXXV5bcV08k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2440152AbfIWRYQ (ORCPT ); Mon, 23 Sep 2019 13:24:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:37200 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2393200AbfIWRYP (ORCPT ); Mon, 23 Sep 2019 13:24:15 -0400 Received: from mail-wr1-f45.google.com (mail-wr1-f45.google.com [209.85.221.45]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D47C92190F for ; Mon, 23 Sep 2019 17:24:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1569259455; bh=DzycgKHCi19mMx4cgC/hY8TzO4MUiU13rQpq2YThoZE=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=AgJtVR2zD2ID/COVmKJzNcv7L5FFBker86qUiq8xMUdR/grog+vdfoPdz1kl1i+2L 3n8nUR6vNH6n2v3jWM0ceUb6UNpa3UdN0CZnhldbm2yHmP8a/ZloneXsUX2qePAseX 7i/HLWr7tZbO8sx5lZGhoke2RMA9qDKtn6GgR5I4= Received: by mail-wr1-f45.google.com with SMTP id i1so14900512wro.4 for ; Mon, 23 Sep 2019 10:24:14 -0700 (PDT) X-Gm-Message-State: APjAAAVC72GQXB50Aa3Oe52wX9AtAznId86v4J1pIxLp0LZFbngkO7rj jQusMwx1BrNxyPD3uU0QREI2LpSJ57pMUDGSZ5PjIQ== X-Google-Smtp-Source: APXvYqzcNw/Fw315XYUmtYdbQHBHfab17/P4MaPRH38Ob6gFaeYiPSmAfE5s06olKUIUuopNukGDlqBjM+ujZLSvy+8= X-Received: by 2002:adf:cc0a:: with SMTP id x10mr362155wrh.195.1569259453239; Mon, 23 Sep 2019 10:24:13 -0700 (PDT) MIME-Version: 1.0 References: <20190919150314.054351477@linutronix.de> <20190919150809.446771597@linutronix.de> <20190923084718.GG2349@hirez.programming.kicks-ass.net> <20190923114920.GF2332@hirez.programming.kicks-ass.net> <20190923115551.GZ2386@hirez.programming.kicks-ass.net> <20190923121001.GG2332@hirez.programming.kicks-ass.net> In-Reply-To: <20190923121001.GG2332@hirez.programming.kicks-ass.net> From: Andy Lutomirski Date: Mon, 23 Sep 2019 10:24:01 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC patch 10/15] x86/entry: Move irq tracing to C code To: Peter Zijlstra Cc: Thomas Gleixner , LKML , X86 ML , Andy Lutomirski , Catalin Marinas , Will Deacon , Mark Rutland , Marc Zyngier , Paolo Bonzini , kvm list , linux-arch , Juergen Gross Content-Type: text/plain; charset="UTF-8" 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 5:10 AM Peter Zijlstra wrote: > > On Mon, Sep 23, 2019 at 01:55:51PM +0200, Peter Zijlstra wrote: > > 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. > > --- > 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 ... Yes, please, but can you add an assertion under CONFIG_DEBUG_ENTRY that IRQs are actually off?