From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35216) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fb3Xs-0002ue-5L for qemu-devel@nongnu.org; Thu, 05 Jul 2018 08:39:37 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fb3Xo-0006FZ-Ul for qemu-devel@nongnu.org; Thu, 05 Jul 2018 08:39:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37280) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fb3Xo-0006AT-O5 for qemu-devel@nongnu.org; Thu, 05 Jul 2018 08:39:32 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 3738D75192 for ; Thu, 5 Jul 2018 12:39:31 +0000 (UTC) Date: Thu, 5 Jul 2018 13:39:29 +0100 From: "Richard W.M. Jones" Message-ID: <20180705123929.GB16293@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Subject: [Qemu-devel] Byte ordering of VM Generation ID in Windows VMs List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org, lersek@redhat.com, mst@redhat.com, berrange@redhat.com, jferlan@redhat.com I was doing a bit of investigation around how different hypervisors handle the VM Generation ID feature. QEMU's behaviour seems quite strange, I wonder if this is a bug or expected? (1) I booted a Windows 2016 VM with: qemu-system-x86_64 -M pc,accel=kvm -m 2G -hda w2k16-mincore.img \ -device vmgenid,guid=01020304-0506-0708-090a-0b0c0d0e0f00,id=vmgenid0 (2) Inside the guest I used the VMGENID.EXE program from: https://bugzilla.redhat.com/show_bug.cgi?id=1598350#c3 https://docs.microsoft.com/en-gb/windows/desktop/HyperV_v2/virtual-machine-generation-identifier Note this is self-compiled using mingw64-g++ (not using Visual Studio which I don't have available), but I don't believe that could have caused the problem. (3) The program prints: VmCounterValue: 708050601020304:f0e0d0c0b0a09 To make it easier to see, this is the same number but zero-extended: VmCounterValue: 07 08 05 06 01 02 03 04 : 00 0f 0e 0d 0c 0b 0a 09 \________ LOW ________/ \_______ HIGH _______/ WORD WORD As you can see it looks like there is no clear relationship between the order of the bytes in the guid= parameter and the order that they are seen by Windows. BTW if you want to try to reproduce this you will need to use Windows 2012 R2 or above. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/