Received: by 10.223.185.116 with SMTP id b49csp393418wrg; Tue, 20 Feb 2018 00:53:58 -0800 (PST) X-Google-Smtp-Source: AH8x225C+eUASan/KGuj2RDpOtE+erInkSj6mKN5CrYnIyC7SdSYwtuQYXoDx6R6Jz7J5hDFyRPL X-Received: by 2002:a17:902:5269:: with SMTP id z96-v6mr4987326plh.385.1519116838156; Tue, 20 Feb 2018 00:53:58 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1519116838; cv=none; d=google.com; s=arc-20160816; b=utcC4pbiqIY+WLPSh2KqABBCQqaZ2EhXBEpOjdQfvCcHQSuR8gzxeqV9xCBa2aerQW SczmdeMsruQKQhoq9LqI6p9lR7bQRrmK9/6EtDP3YogVGTBUNFdmE4Y5HpaQCG+5nVBN CTJnGTHYhG2pDXhFcOSe6mR0eanwVySKk7qJwBOjbZbZhNUJWpaLAAN9NiTWh7vx3AYw pMJhY4wU0M9n1/F+6IpUulEXP9AtX6cCN5x/tO9mcElCp3QU2oVyjWFRUSZsoJiiffEj cPY1nXA86Ln0wEAoTc+61YPJkmdDUXnQ1x4NIK4vq4JHME4n1hB4+Ug6WmW0KniSSf4M 8d6A== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:mime-version:user-agent:references :message-id:in-reply-to:subject:cc:to:from:date :arc-authentication-results; bh=4rGm6WsCNTLqRXbIdQbLkqKDZdLv18LBe8WRV7YALmY=; b=FAexbDX4PQLO6m1LaU85hwOCpUc1oK23jigpITDM0BfjR9wg3rpd1eWUGCF5ov070E GAe0w9WLCpXGkKDu9OQpoNuZS8aa3v6Se6VDSCFihV+dm/8HX+5lTa3lVpLvu/oa8Uqq 6Pa6KyhLD+X5q1Pjj9T0x+Cn/ugCsbbX8orgb5wyY5xvJBB3kcuAqLIBNmM0PzOL/hqT o5HcBmyt/aQ6WT8ghVnzIJgGxHhcNWoH1USHC9G/DGMkK+eT/nF5W3Ws8RGD/7R7b+cH 0YrDVPvxEkLu4x35jRqrciCcxd+QYDCfS6JrjnTfa8/SnrMLokTMz/NwVacTe02FqvAR DUeg== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id q11si6165067pfd.242.2018.02.20.00.53.44; Tue, 20 Feb 2018 00:53:58 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751399AbeBTIwz (ORCPT + 99 others); Tue, 20 Feb 2018 03:52:55 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:60841 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750781AbeBTIwy (ORCPT ); Tue, 20 Feb 2018 03:52:54 -0500 Received: from [37.80.9.43] by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1eo3bw-0002Ic-Br; Tue, 20 Feb 2018 09:49:16 +0100 Date: Tue, 20 Feb 2018 09:52:50 +0100 (CET) From: Thomas Gleixner To: Linus Torvalds cc: Alan Cox , "Van De Ven, Arjan" , "valdis.kletnieks@vt.edu" , Jon Masters , David Woodhouse , Paolo Bonzini , "x86@kernel.org" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Hansen, Dave" , Ingo Molnar Subject: Re: [PATCH 2/2] x86/speculation: Support "Enhanced IBRS" on future CPUs In-Reply-To: Message-ID: References: <1518449255-2182-1-git-send-email-dwmw@amazon.co.uk> <1518449255-2182-2-git-send-email-dwmw@amazon.co.uk> <7e2e5ad1-49b6-1fdb-4a62-8ad6aefc30a0@redhat.com> <1518509708.12890.33.camel@infradead.org> <27c85759-e662-d281-f8a0-0a80ca8ee18f@redhat.com> <1518517262.12890.43.camel@infradead.org> <1518518198.12890.48.camel@infradead.org> <02bd3fdd-1b73-6cab-fb09-38ba933396bd@redhat.com> <1518775136.7876.13.camel@infradead.org> <75287047-77a0-e0ff-c2e8-61c81641251e@redhat.com> <1518776517.7876.21.camel@infradead.org> <1518783021.7876.34.camel@infradead.org> <4882860e-23c5-75b3-ac02-c700f615156e@jonmasters.org> <0575AF4FD06DD142AD198903C74E1CC87A61923C@ORSMSX103.amr.corp.intel.com> <10373.1519084385@turing-police.cc.vt.edu> <0575AF4FD06DD142AD198903C74E1CC87A619255@ORSMSX103.amr.corp.intel.com> <20180220001301.70101e1d@alans-desktop> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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 On Mon, 19 Feb 2018, Linus Torvalds wrote: > On Mon, Feb 19, 2018 at 4:13 PM, Alan Cox wrote: > > > > In theory there's nothing stopping a guest getting a 'you are about to > > gain/lose IBRS' message or having a new 'CPU' hotplugged and the old one > > removed. > > I'm not convinced we handle the case of hotplug CPU's with different > CPU models correctly. > > In fact, I'd be very surprised it it worked in the general case. We pretend to work with different CPU models mostly by having per cpu feature bits, but in practice this would fall apart in bits and pieces all over the place. Thanks, tglx