From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: 2.6.27, kvm-kmod, and PCI device assignment Date: Mon, 12 Sep 2011 20:05:19 +0200 Message-ID: <4E6E49DF.3000303@siemens.com> References: <4E6E47DE.6080602@genband.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, Avi Kivity , mtosatti@redhat.com, David Ahern To: Chris Friesen Return-path: Received: from thoth.sbs.de ([192.35.17.2]:33330 "EHLO thoth.sbs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751819Ab1ILSFe (ORCPT ); Mon, 12 Sep 2011 14:05:34 -0400 In-Reply-To: <4E6E47DE.6080602@genband.com> Sender: kvm-owner@vger.kernel.org List-ID: On 2011-09-12 19:56, Chris Friesen wrote: > > Hi, > > I've been away a bit but I'm now coming back to this issue. > > Is it expected that the kvm-kmod modules will allow PCI device > assignment (aka VT-d) with older kernels? If so, then is there an > expectation for how far back it will be supported? I haven't seen a > clear statement of this anywhere, and I think David was interested in > this as well. In general, it is supposed to work, but there are likely more quirks and limitation than with a recent kernel. Example: pci_reset_function is not available for < 2.6.28, thus the assigned device may not work properly if the guest depends on a reset or after the VM ran through a reset or . You may also run into bugs/limitations of required kernel subsystems like the IOMMU layer that were fixed in newer kernels. kvm-kmod only addresses the kvm modules here. > > Looking at the instructions at > "http://www.linux-kvm.org/page/How_to_assign_devices_with_VT-d_in_KVM", > step 4 is to unbind the device from the host using the "pci_stub" > functionality. That code was only added to mainline for 2.6.29-rc1, so > it seems like extra work will be needed for 2.6.28 and earlier. pci_stub is not strictly required if you manage your system in a way that all other "interested" drivers are kept away from the assigned device. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux