From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v2 16/17] kvm: x86: Rework identity map and TSS setup for larger BIOS sizes Date: Mon, 03 Jan 2011 18:59:49 +0200 Message-ID: <4D220085.3040200@redhat.com> References: <4D21F416.9090300@redhat.com> <4D21FECD.9000103@web.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , kvm@vger.kernel.org, qemu-devel@nongnu.org, Jan Kiszka To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:56979 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754488Ab1ACQ74 (ORCPT ); Mon, 3 Jan 2011 11:59:56 -0500 In-Reply-To: <4D21FECD.9000103@web.de> Sender: kvm-owner@vger.kernel.org List-ID: On 01/03/2011 06:52 PM, Jan Kiszka wrote: > Am 03.01.2011 17:06, Avi Kivity wrote: > > On 01/03/2011 10:33 AM, Jan Kiszka wrote: > >> From: Jan Kiszka > >> > >> First of all, we only need this EPT identity and TSS reservation on > >> Intel CPUs. > > > > kvm-amd will ignore it just fine. I'd like to keep arch differences > > away from userspace. > > And I would prefer to avoid needlessly cluttering the physical guest > address space where not needed. Long term, we could even give user space > a hint (unless it can test it directly) that this workaround is no > longer needed as the host Intel CPU supports true real mode. Having different physical address spaces based on the host cpu is bad, even disregarding live migration. If there's a real need, we can do it as an option. I don't see such a need though. We can definitely add a new KVM_CAP for "tss/ept identity supported but not needed". If emulate_invalid_guest_state is eventually fully implemented and becomes the default, it will even be true across the board. > > > >> Then, in order to support loading BIOSes> 256K, reorder the > >> code, adjusting the base if the kernel supports moving the identity map. > >> We can drop the check for KVM_CAP_SET_TSS_ADDR as we already depend on > >> much newer features. > > > > There is no ordering on kvm features. Each can come and go as it pleases. > > > > Well, at least this is not how kvm upstream works so far. Let's change it then. -- error compiling committee.c: too many arguments to function