From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH v3 18/24] xen/passthrough: iommu_deassign_device_dt: By default reassign device to nobody Date: Mon, 23 Feb 2015 15:34:55 +0000 Message-ID: <1424705695.27930.168.camel@citrix.com> References: <1421159133-31526-1-git-send-email-julien.grall@linaro.org> <1421159133-31526-19-git-send-email-julien.grall@linaro.org> <1424451889.30924.363.camel@citrix.com> <54EAFCA5.2050905@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta4.messagelabs.com ([85.158.143.247]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1YPv3x-0003lG-T3 for xen-devel@lists.xenproject.org; Mon, 23 Feb 2015 15:36:50 +0000 In-Reply-To: <54EAFCA5.2050905@linaro.org> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Julien Grall Cc: xen-devel@lists.xenproject.org, tim@xen.org, Jan Beulich , stefano.stabellini@citrix.com List-Id: xen-devel@lists.xenproject.org On Mon, 2015-02-23 at 10:10 +0000, Julien Grall wrote: > > On 20/02/2015 17:04, Ian Campbell wrote: > > On Tue, 2015-01-13 at 14:25 +0000, Julien Grall wrote: > >> Currently, when the device is deassigned from a domain, we directly reassign > >> to DOM0. > >> > >> As the device may not have been correctly reset, this may lead to corruption or > >> expose some part of DOM0 memory. Also, we may have no way to reset some > >> platform devices. > >> > >> If Xen reassigns the device to "nobody", it may receive some global/context > >> fault because the transaction has failed (indeed the context has been > >> marked invalid). Unfortunately there is no simple way to quiesce a buggy > >> hardware. I think we could live with that for a first version of platform > >> device passthrough. > >> > >> DOM0 will have to issue an hypercall to assign the device to itself if it > >> wants to use it. > > > > Does this behaviour differ from x86? I realise now that x86 is a red-herring, what I really meant was differ from other types of device (specifically PCI ones). > If so then it is worth calling that > > out explicitly (even if not, good to know I think!) > > What do you mean by "calling that out explicitly"? Stating in the commit log or a suitably placed comment (at least under xen/include/public hopefully) that deassignment of dt devices behaves differently to deassignment of other types of devices. Ian.