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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 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 26313C433E0 for ; Thu, 14 May 2020 00:13:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 44035205ED for ; Thu, 14 May 2020 00:13:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733077AbgENANy (ORCPT ); Wed, 13 May 2020 20:13:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:41786 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732981AbgENANx (ORCPT ); Wed, 13 May 2020 20:13:53 -0400 Received: from oasis.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 5D0362065C; Thu, 14 May 2020 00:13:51 +0000 (UTC) Date: Wed, 13 May 2020 20:13:49 -0400 From: Steven Rostedt To: Mathieu Desnoyers Cc: Thomas Gleixner , linux-kernel , x86 , paulmck , Andy Lutomirski , Alexandre Chartre , Frederic Weisbecker , Paolo Bonzini , Sean Christopherson , Masami Hiramatsu , Petr Mladek , "Joel Fernandes, Google" , Boris Ostrovsky , Juergen Gross , Brian Gerst , Josh Poimboeuf , Will Deacon Subject: Re: [patch V4 part 1 14/36] x86/entry: Get rid of ist_begin/end_non_atomic() Message-ID: <20200513201349.35132f23@oasis.local.home> In-Reply-To: <1777514130.20137.1589410645669.JavaMail.zimbra@efficios.com> References: <20200505131602.633487962@linutronix.de> <20200505134059.462640294@linutronix.de> <1777514130.20137.1589410645669.JavaMail.zimbra@efficios.com> 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, 13 May 2020 18:57:25 -0400 (EDT) Mathieu Desnoyers wrote: > ----- On May 5, 2020, at 9:16 AM, Thomas Gleixner tglx@linutronix.de wrote: > > > This is completely overengineered and definitely not an interface which > > should be made available to anything else than this particular MCE case. > > This patch introduces a significant change under the radar (not explained > in the changelog): it turns preempt_enable_no_resched() into preempt_enable(). > > Why, and why was it a no_resched() in the first place ? Was it for performance > or correctness reasons ? I believe the reason for no_resched, is because it was within a local_irq_disable() section, which means it couldn't schedule anyway. -- Steve > > --- a/arch/x86/kernel/cpu/mce/core.c > > +++ b/arch/x86/kernel/cpu/mce/core.c > > @@ -1352,13 +1352,15 @@ void notrace do_machine_check(struct pt_ > > > > /* Fault was in user mode and we need to take some action */ > > if ((m.cs & 3) == 3) { > > - ist_begin_non_atomic(regs); > > + /* If this triggers there is no way to recover. > > Die hard. */ > > + BUG_ON(!on_thread_stack() || !user_mode(regs)); > > local_irq_enable(); > > + preempt_enable(); > > > > if (kill_it || do_memory_failure(&m)) > > force_sig(SIGBUS); > > + preempt_disable(); > > local_irq_disable(); > > - ist_end_non_atomic(); > > } else { > > if (!fixup_exception(regs, X86_TRAP_MC, error_code, > > -void ist_begin_non_atomic(struct pt_regs *regs) > > -{ > > - BUG_ON(!user_mode(regs)); > > - > > - /* > > - * Sanity check: we need to be on the normal thread > > stack. This > > - * will catch asm bugs and any attempt to use > > ist_preempt_enable > > - * from double_fault. > > - */ > > - BUG_ON(!on_thread_stack()); > > - > > - preempt_enable_no_resched(); > > -} > > - > > -/** > > - * ist_end_non_atomic() - begin a non-atomic section in an IST > > exception > > - * > > - * Ends a non-atomic section started with ist_begin_non_atomic(). > > - */ > > -void ist_end_non_atomic(void) > > -{ > > - preempt_disable(); > > -} > > - > > int is_valid_bugaddr(unsigned long addr) > > { > > unsigned short ud; >