From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: (v2) Design proposal for RMRR fix Date: Wed, 14 Jan 2015 12:14:15 +0000 Message-ID: <1421237655.19103.242.camel@citrix.com> References: <54B3A2D602000078000538A2@mail.emea.novell.com> <54B3A71002000078000538E1@mail.emea.novell.com> <54B3AB380200007800053917@mail.emea.novell.com> <54B3AE8802000078000539B7@mail.emea.novell.com> <54B54C09020000780005472D@mail.emea.novell.com> <54B5411F.8060208@eu.citrix.com> <54B5509402000078000547A5@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: "Tian, Kevin" Cc: "wei.liu2@citrix.com" , "stefano.stabellini@eu.citrix.com" , George Dunlap , "tim@xen.org" , "ian.jackson@eu.citrix.com" , "xen-devel@lists.xen.org" , Jan Beulich , "Zhang, Yang Z" , "Chen, Tiejun" List-Id: xen-devel@lists.xenproject.org On Wed, 2015-01-14 at 06:52 +0000, Tian, Kevin wrote: > > From: Jan Beulich [mailto:JBeulich@suse.com] > > Sent: Wednesday, January 14, 2015 12:06 AM > > > > >>> On 13.01.15 at 17:00, wrote: > > > Another option I was thinking about: Before assigning a device to a > > > guest, you have to unplug the device and assign it to pci-back (e.g., > > > with xl pci-assignable-add). In addition to something like rmmr=host, > > > we could add rmrr=assignable, which would add all of the RMRRs of all > > > devices currently listed as "assignable". The idea would then be that > > > you first make all your devices assignable, then just start your guests, > > > and everything you've made assignable will be able to be assigned. > > > > Nice idea indeed, but I'm not sure about its practicability: It may > > not be desirable to make all devices eventually to be handed to a > > guest prior to starting any of the guests it may get handed to. In > > particular there may be reasons why the host needs the device > > while (or until after) creating the guests. > > > > and I'm not sure whether there's enough knowledge to judge whether > a device is assignable since potential conflicts may be detected only > when the guest is launched. I don't think George was intending to imply otherwise, assignable here just means "bound to xen-pciback", there may be other reasons why the device cannot be assigned in practice when you come to actually use it, i.e. RMRR conflicts which may only be discovered when a guest is started would be one such practical reason. George's suggestion sounds to me like a nice shortcut configuration which will benefit many users, even if not all of them. So long as more fine grained control is an option itseems like a Nice To Have type thing. Ian.