From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752264AbdKHLzQ (ORCPT ); Wed, 8 Nov 2017 06:55:16 -0500 Received: from mx2.suse.de ([195.135.220.15]:47550 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751969AbdKHLzO (ORCPT ); Wed, 8 Nov 2017 06:55:14 -0500 Subject: Re: [Xen-devel] [PATCH 3/3] x86/xen: use guest_late_init to detect Xen PVH guest To: Jan Beulich Cc: len.brown@intel.com, x86@kernel.org, tglx@linutronix.de, xen-devel@lists.xenproject.org, boris.ostrovsky@oracle.com, mingo@redhat.com, pbonzini@redhat.com, rkrcmar@redhat.com, rjw@rjwysocki.net, pavel@ucw.cz, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, hpa@zytor.com References: <20171108090739.26491-1-jgross@suse.com> <20171108090739.26491-4-jgross@suse.com> <5A02F633020000780018D26A@suse.com> From: Juergen Gross Message-ID: Date: Wed, 8 Nov 2017 12:55:11 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <5A02F633020000780018D26A@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/11/17 12:18, Jan Beulich wrote: >>>> On 08.11.17 at 10:07, wrote: >> In case we are booted via the default boot entry by a generic loader >> like grub or OVMF it is necessary to distinguish between a HVM guest >> with a device model supporting legacy devices and a PVH guest without >> device model. >> >> PVH guests will always have x86_platform.legacy.no_vga set and >> x86_platform.legacy.rtc cleared, while both won't be true for HVM >> guests. >> >> Test for both conditions in the guest_late_init hook and set xen_pvh >> to true if they are met. > > This sounds pretty fragile to me: I can't see a reason why a proper > HVM guest couldn't come without VGA and RTC. That's not possible > today, agreed, but certainly an option down the road if virtualization > follows bare metal's road towards being legacy free. >>From guest's perspective: what is the difference between a legacy free HVM domain and PVH? In the end the need for differentiating is to avoid access to legacy features in PVH as those would require a device model. Juergen