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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 9A977C433E2 for ; Wed, 2 Sep 2020 16:24:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 83BB72072A for ; Wed, 2 Sep 2020 16:24:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727824AbgIBQYb (ORCPT ); Wed, 2 Sep 2020 12:24:31 -0400 Received: from mx2.suse.de ([195.135.220.15]:49004 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726310AbgIBQYa (ORCPT ); Wed, 2 Sep 2020 12:24:30 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id BD49CAD03; Wed, 2 Sep 2020 16:24:29 +0000 (UTC) Subject: Re: [PATCH 01/13] x86/entry: Fix AC assertion To: Brian Gerst , Peter Zijlstra Cc: the arch/x86 maintainers , Linux Kernel Mailing List , Kyle Huey , Alexandre Chartre , Robert O'Callahan , "Paul E. McKenney" , Frederic Weisbecker , Paolo Bonzini , Sean Christopherson , Masami Hiramatsu , Petr Mladek , Steven Rostedt , Joel Fernandes , Boris Ostrovsky , Andy Lutomirski , Josh Poimboeuf , Daniel Thompson , Andrew Cooper References: <20200902132549.496605622@infradead.org> <20200902133200.666781610@infradead.org> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Message-ID: Date: Wed, 2 Sep 2020 18:24:27 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02.09.20 17:58, Brian Gerst wrote: > On Wed, Sep 2, 2020 at 9:38 AM Peter Zijlstra wrote: >> >> From: Peter Zijlstra >> >> The WARN added in commit 3c73b81a9164 ("x86/entry, selftests: Further >> improve user entry sanity checks") unconditionally triggers on my IVB >> machine because it does not support SMAP. >> >> For !SMAP hardware we patch out CLAC/STAC instructions and thus if >> userspace sets AC, we'll still have it set after entry. >> >> Fixes: 3c73b81a9164 ("x86/entry, selftests: Further improve user entry sanity checks") >> Signed-off-by: Peter Zijlstra (Intel) >> Acked-by: Andy Lutomirski >> --- >> arch/x86/include/asm/entry-common.h | 11 +++++++++-- >> 1 file changed, 9 insertions(+), 2 deletions(-) >> >> --- a/arch/x86/include/asm/entry-common.h >> +++ b/arch/x86/include/asm/entry-common.h >> @@ -18,8 +18,16 @@ static __always_inline void arch_check_u >> * state, not the interrupt state as imagined by Xen. >> */ >> unsigned long flags = native_save_fl(); >> - WARN_ON_ONCE(flags & (X86_EFLAGS_AC | X86_EFLAGS_DF | >> - X86_EFLAGS_NT)); >> + unsigned long mask = X86_EFLAGS_DF | X86_EFLAGS_NT; >> + >> + /* >> + * For !SMAP hardware we patch out CLAC on entry. >> + */ >> + if (boot_cpu_has(X86_FEATURE_SMAP) || >> + (IS_ENABLED(CONFIG_64_BIT) && boot_cpu_has(X86_FEATURE_XENPV))) >> + mask |= X86_EFLAGS_AC; > > Is the explicit Xen check necessary? IIRC the Xen hypervisor will > filter out the SMAP bit in the cpuid pvop. Right, and this test will nevertheless result in setting AC in the mask. IIRC this was the main objective here. Juergen