Re: [Xen-devel] Xen 4.2 and PCI hotplug.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.12.12 at 15:36, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> On 19/12/2012 09:14, Zhang, Xiantao wrote:
>>> -----Original Message-----
>>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>>> 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" <xiantao.zhang@xxxxxxxxx>
>>> 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.

Jan


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