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=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 DE527C433E1 for ; Fri, 21 Aug 2020 07:47:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A8C4120738 for ; Fri, 21 Aug 2020 07:47:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="juC3rw6m" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728135AbgHUHrp (ORCPT ); Fri, 21 Aug 2020 03:47:45 -0400 Received: from mail.skyhub.de ([5.9.137.197]:55462 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725908AbgHUHro (ORCPT ); Fri, 21 Aug 2020 03:47:44 -0400 Received: from zn.tnic (p200300ec2f0eda00b4e1d8975031aaf0.dip0.t-ipconnect.de [IPv6:2003:ec:2f0e:da00:b4e1:d897:5031:aaf0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 522451EC013E; Fri, 21 Aug 2020 09:47:43 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1597996063; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=x0qqa/IvqrLY60Nv10kXxs4ZIliJBY04I896OOhUGRs=; b=juC3rw6mRkclVIO9LDa0WrzWnTCqKSyhGOm2CZ5oQY1OW1o37YT2e/7Q/fzIblYhrqVhXM cAzBNBKLHa+HLide6l50783CgJZIn/YZbkq+OmkwWjwMTgzUOMiDlUaNEiKoBboXSnGqd/ aXtqVIr/+gWx0Una9QOIpG/Md4MpqeI= Date: Fri, 21 Aug 2020 09:47:43 +0200 From: Borislav Petkov To: Sean Christopherson Cc: Andy Lutomirski , Thomas Gleixner , Ingo Molnar , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org, Dave Hansen , Chang Seok Bae , Peter Zijlstra , Sasha Levin , Paolo Bonzini , kvm@vger.kernel.org, Tom Lendacky Subject: Re: [PATCH] x86/entry/64: Disallow RDPID in paranoid entry if KVM is enabled Message-ID: <20200821074743.GB12181@zn.tnic> References: <20200821025050.32573-1-sean.j.christopherson@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200821025050.32573-1-sean.j.christopherson@intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 20, 2020 at 07:50:50PM -0700, Sean Christopherson wrote: > + * Disallow RDPID if KVM is enabled as it may consume a guest's TSC_AUX > + * if an NMI arrives in KVM's run loop. KVM loads guest's TSC_AUX on > + * VM-Enter and may not restore the host's value until the CPU returns > + * to userspace, i.e. KVM depends on the kernel not using TSC_AUX. > */ And frankly, this is really unfair. The kernel should be able to use any MSR. IOW, KVM needs to be fixed here. I'm sure it context-switches other MSRs so one more MSR is not a big deal. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette