From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: Cross vendor migration ideas Date: Wed, 12 Nov 2008 09:45:58 -0600 Message-ID: <491AFA36.4040909@codemonkey.ws> References: <45680888-AF1B-42B6-B0A7-EE635F44E2A2@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "kvm@vger.kernel.org list" , Amit Shah , Avi Kivity , Elsie Wahlig , "Serebrin, Benjamin (Calendar)" , "Nakajima, Jun" To: Alexander Graf Return-path: Received: from yx-out-2324.google.com ([74.125.44.28]:65238 "EHLO yx-out-2324.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752696AbYKLPqD (ORCPT ); Wed, 12 Nov 2008 10:46:03 -0500 Received: by yx-out-2324.google.com with SMTP id 8so207220yxm.1 for ; Wed, 12 Nov 2008 07:46:02 -0800 (PST) In-Reply-To: <45680888-AF1B-42B6-B0A7-EE635F44E2A2@suse.de> Sender: kvm-owner@vger.kernel.org List-ID: Alexander Graf wrote: > Hi, > > I was thinking a bit about cross vendor migration recently and since > we're doing open source development, I figured it might be a good idea > to talk to everyone about this. > > So why are we having a problem? > > In normal operation we don't. If we're running a 32-bit kernel, we can > use SYSENTER to jump from kernel<->userspace. If we're on a 64-bit > kernel with 64-bit userspace, every CPU supports SYSCALL. At least > Linux is being smart on this and does use exactly these two > capabilities in these two cases. > But if we're running in compat mode (64-bit kernel with 32-bit > userspace), things differ. Intel supports only SYSENTER here, while > AMD only supports SYSCALL. Both can still use int80. Obviously we can trap-and-emulate but that would be slow in a relatively fast past. I wonder if patching is an option? Regards, Anthony Liguori