From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sheng Yang Subject: Re: Question about guest MSR loading/saving (Intel) Date: Tue, 2 Feb 2010 10:53:23 +0800 Message-ID: <201002021053.23730.sheng@linux.intel.com> References: <0910BB5A-E4FA-4085-978E-D6374A1376B7@gmail.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Cc: Kurt Kiefer To: kvm@vger.kernel.org Return-path: Received: from mga09.intel.com ([134.134.136.24]:63216 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753327Ab0BBC4o (ORCPT ); Mon, 1 Feb 2010 21:56:44 -0500 In-Reply-To: <0910BB5A-E4FA-4085-978E-D6374A1376B7@gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: On Tuesday 02 February 2010 09:57:08 Kurt Kiefer wrote: > Hi all, > > This is a vague/general question. For some background: I have a reason > (control of IA32_PERF_GLOBAL_CTRL) for loading/saving MSRs on VM-entry/ > exit. To get this to work correctly, I made changes to use the > conventional VMX MSR load areas of the VMCS for this particular MSR. > Works great. > > Is there a particular reason why MSRs are currently loaded/saved > through KVM's unconventional facilities (vmx.c:save_msrs(), > vmx.c:load_msrs()), rather than through VM entry/exit MSR load regions > in the VMCS? I see that only long mode guests on x86_64 are effected > by this. > > Any insight could be useful. Do you think MSR loading via VMCS would > be faster? Are there downsides to doing it one way or the other? > Because not all MSRs are supported for automatically save/load when VMX transition happened. You used IA32_PERF_GLOBAL_CTRL is supported. But not the ones saved in save_msrs(). -- regards Yang, Sheng