From mboxrd@z Thu Jan 1 00:00:00 1970 From: Glauber Costa Subject: Re: [patch 09/18] KVM: x86: introduce facility to support vsyscall pvclock, via MSR Date: Mon, 29 Oct 2012 18:45:43 +0400 Message-ID: <508E9697.2000003@parallels.com> References: <20121024131340.742340256@redhat.com> <20121024131621.707068244@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Cc: , , , , , , To: Marcelo Tosatti Return-path: Received: from mx2.parallels.com ([64.131.90.16]:33196 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750942Ab2J2Opv (ORCPT ); Mon, 29 Oct 2012 10:45:51 -0400 In-Reply-To: <20121024131621.707068244@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 10/24/2012 05:13 PM, Marcelo Tosatti wrote: > Allow a guest to register a second location for the VCPU time info > > structure for each vcpu (as described by MSR_KVM_SYSTEM_TIME_NEW). > This is intended to allow the guest kernel to map this information > into a usermode accessible page, so that usermode can efficiently > calculate system time from the TSC without having to make a syscall. > > Signed-off-by: Marcelo Tosatti Can you please be a bit more specific about why we need this? Why does the host need to provide us with two pages with the exact same data? Why can't just do it with mapping tricks in the guest?