From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: Xen 4.2 and PCI hotplug. Date: Fri, 21 Dec 2012 16:13:34 -0500 Message-ID: <20121221211334.GB32523@phenom.dumpdata.com> References: <20121218224606.GA6918@phenom.dumpdata.com> <50D18D4E02000078000B15B3@nat28.tlf.novell.com> <50D1D0E8.7050203@citrix.com> <50D1E67F02000078000B1791@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <50D1E67F02000078000B1791@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: Andrew Cooper , xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On Wed, Dec 19, 2012 at 03:08:31PM +0000, Jan Beulich wrote: > >>> On 19.12.12 at 15:36, Andrew Cooper wrote: > > On 19/12/2012 09:14, Zhang, Xiantao wrote: > >>> -----Original Message----- > >>> From: Jan Beulich [mailto:JBeulich@suse.com] > >>> Sent: Wednesday, December 19, 2012 4:48 PM > >>> To: Zhang, Xiantao > >>> Cc: Konrad Rzeszutek Wilk; xen-devel > >>> Subject: Re: [Xen-devel] Xen 4.2 and PCI hotplug. > >>> > >>>>>> On 19.12.12 at 09:13, "Zhang, Xiantao" > >>> wrote: > >>>> Are you playing with Xen ? so far, Xen doesn't support PCIe device > >>>> hot-plug feature yet. > >>> When saying Xen, I assume you mean the pv-ops kernel instead? So far I was > >>> under the impression that this worked even with the very old 2.6.18 tree (as > >>> much or as little as hotplug there worked in the native case). And given > > that > >>> there are no special requirements on the hypervisor to make this work, it's > >>> not even obvious to me what would be missing in the pv-ops kernel to make > >>> it work. > >> Oh, my fault! Perhaps we don't need to do anything for pv-ops kernel to > > support device hot-plug if native system has it supported. Actually, we > > didn't do such testings before, since it is a native feature, not a > > Xen-specific one. > >> Xiantao > > > > My current understanding is that on boot, Xen scans the PCI bus, then > > dom0 rescans it later. If a hotplug event gets serviced by dom0, does > > there not need to be some hypercall informing Xen that a new device has > > appeared? I expect PCIPassthrough would not work correctly on a > > hotplugged device which Xen is unaware of. > > Sure - such a hypercall exists and is - from all I can tell - being made > not only during the boot time bus scan, but also during hotplug > processing. See drivers/xen/pci.c. Right. What I am not sure about - and this is why I am asking Intel - whether that notifier gets called _after_ dom0 has interogated the new PCI device. And if so, would Xen (which gets trapped on the 0xcf8) would not let dom0 actually interogate the new BDF b/c it hasn't been told about this BDF existence. This is all speculation - and I might be very well completly wrong about all of this - hence this email-thread. Testing would of course tell for sure, but I am not sure if I even have such hardware. > > Jan > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel >