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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 D94F1C433E0 for ; Wed, 10 Jun 2020 22:09:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AAA5C2072E for ; Wed, 10 Jun 2020 22:09:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726576AbgFJWJM (ORCPT ); Wed, 10 Jun 2020 18:09:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50210 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726374AbgFJWJL (ORCPT ); Wed, 10 Jun 2020 18:09:11 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8F672C03E96B for ; Wed, 10 Jun 2020 15:09:11 -0700 (PDT) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jj8tt-0004e0-G2; Thu, 11 Jun 2020 00:08:49 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id C6DEC100F18; Thu, 11 Jun 2020 00:08:48 +0200 (CEST) From: Thomas Gleixner To: Sean Christopherson Cc: "David P. Reed" , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Allison Randal , Enrico Weigelt , Greg Kroah-Hartman , Kate Stewart , "Peter Zijlstra \(Intel\)" , Randy Dunlap , Martin Molnar , Andy Lutomirski , Alexandre Chartre , Jann Horn , Dave Hansen , linux-kernel@vger.kernel.org Subject: Re: [PATCH] Fix undefined operation VMXOFF during reboot and crash In-Reply-To: <20200610214231.GH18790@linux.intel.com> References: <20200610181254.2142-1-dpreed@deepplum.com> <878sgufvvm.fsf@nanos.tec.linutronix.de> <20200610214231.GH18790@linux.intel.com> Date: Thu, 11 Jun 2020 00:08:48 +0200 Message-ID: <87wo4evaj3.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sean Christopherson writes: > Gah, I typed too slow :-) Haha. I had the same thought. > On Wed, Jun 10, 2020 at 11:34:21PM +0200, Thomas Gleixner wrote: >> We have exception fixups to avoid exactly that kind of horrible >> workarounds all over the place. >> >> static inline int cpu_vmxoff_safe(void) >> { >> int err; >> >> asm volatile("2: vmxoff; xor %[err],%[err]\n" >> "1:\n\t" >> ".section .fixup,\"ax\"\n\t" >> "3: mov %[fault],%[err] ; jmp 1b\n\t" >> ".previous\n\t" >> _ASM_EXTABLE(2b, 3b) >> : [err] "=a" (err) >> : [fault] "i" (-EFAULT) >> : "memory"); >> return err; >> } >> >> static inline void __cpu_emergency_vmxoff(void) >> { >> if (!cpu_vmx_enabled()) >> return; >> if (!cpu_vmxoff_safe()) >> cr4_clear_bits(X86_CR4_VMXE); > > This bit is wrong, CR4.VMXE should be cleared even if VMXOFF faults, e.g. > if this is called in NMI context and the NMI arrived in KVM code between > VMXOFF and clearing CR4.VMXE. Oh, right. > All other VMXOFF faults are mode related, i.e. any fault is guaranteed to > be due to the !post-VMXON check unless we're magically in RM, VM86, compat > mode, or at CPL>0. Your patch is simpler indeed. Thanks, tglx