From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753759AbaLVWt0 (ORCPT ); Mon, 22 Dec 2014 17:49:26 -0500 Received: from mail-wg0-f49.google.com ([74.125.82.49]:46974 "EHLO mail-wg0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752664AbaLVWtZ (ORCPT ); Mon, 22 Dec 2014 17:49:25 -0500 Message-ID: <54989FF0.3090300@redhat.com> Date: Mon, 22 Dec 2014 23:49:20 +0100 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Andy Lutomirski , Marcelo Tosatti CC: Gleb Natapov , kvm list , "linux-kernel@vger.kernel.org" Subject: Re: Cleaning up the KVM clock References: <20141222133430.GA23631@amt.cnet> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22/12/2014 17:03, Andy Lutomirski wrote: > This is wrong. The guest *kernel* might not see the intermediate > state because the kernel (presumably it disabled migration while > reading pvti), but the guest vdso can't do that and could very easily > observe pvti while it's being written. No. kvm_guest_time_update is called by vcpu_enter_guest, while the vCPU is not running, so it's entirely atomic from the point of view of the guest. > I'll send patches for the whole mess, complete with lots of comments, > after I test them a bit today. Ok, some comments can certainly help the discussion. Paolo