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Re: [Xen-devel] [pvops-dom0] [patch] Hook Linux's PCI probe and remove c

To: "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>
Subject: Re: [Xen-devel] [pvops-dom0] [patch] Hook Linux's PCI probe and remove callbacks
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Mon, 20 Jul 2009 10:01:37 -0700
Cc: "Han, Weidong" <weidong.han@xxxxxxxxx>, "'xen-devel@xxxxxxxxxxxxxxxxxxx'" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Kay, Allen M" <allen.m.kay@xxxxxxxxx>, 'Keir Fraser' <Keir.Fraser@xxxxxxxxxxxxx>, Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>
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On 07/19/09 04:55, Jiang, Yunhong wrote:
>  One consideration to is to split them into two item:
> a) For all device that is not hot-pluged, we don't need this hypercall, 
> instead, Xen will do the scan and setup the mapping.
> b) For those hot-plug device and SR-IOV devices, maybe we can use the 
> BUS_NOTIFY_ADD_DEVICE notifier to achieve ths purpose. We can just add a 
> notifier to it. I assume this is simlar to IOMMU in kernel, which should 
> requires this notify also. So a Xen specific notifier should achieve our 
> purpose without change to the PCI bus layer. 
> I checked the kernel code, and noticed that arch/x86/kernel/amd_iommu.c 
> register the notifier for BUS_NOTIFY_ADD_DEVICE, but a bit strange why Intel 
> IOMMU has no such support, do you know if VT-d in kernel support device 
> hotplug already?
> Allen/Jeremy, any suggestion?

Yes, this is exactly the kind of answer I was looking for.

> Thanks
> Yunhong Jiang
>> -----Original Message-----
>> From: Kay, Allen M 
>> Sent: 2009年7月18日 7:43
>> To: Jeremy Fitzhardinge; Han, Weidong
>> Cc: 'xen-devel@xxxxxxxxxxxxxxxxxxx'; 'Keir Fraser'; Jiang, Yunhong
>> Subject: RE: [Xen-devel] [pvops-dom0] [patch] Hook Linux's PCI 
>> probe and remove callbacks
>> These hooks for two purposes:
>> 1) Enabling of a SR-IOV virtual function.  The hypercall will 
>> tell xen to setup VT-d context entries for the BDF 
>> corresponding to the new virtual function.  This is required 
>> for SR-IOV to work.
>> 2) PCI hot-plug support when devices are hot added/removed.  
>> Vt-d context entries and data structures in Xen needs to be 
>> modified accordingly.
>> These hooks needs to be enabled before either of these 
>> functions are performed - I assume after dom0 boots.
>> Can you suggest a better way to do this?
>> -----Original Message-----
>> From: Jeremy Fitzhardinge [mailto:jeremy@xxxxxxxx] 
>> Sent: Friday, July 17, 2009 4:14 PM
>> To: Han, Weidong
>> Cc: 'xen-devel@xxxxxxxxxxxxxxxxxxx'; 'Keir Fraser'; Kay, Allen 
>> M; Jiang, Yunhong
>> Subject: Re: [Xen-devel] [pvops-dom0] [patch] Hook Linux's PCI 
>> probe and remove callbacks
>> On 07/15/09 22:15, Han, Weidong wrote:
>>> Hijack the pci_bus_type probe and remove callbacks. This option only
>>> requires modification to the Xen specific part of Linux.
>>> This is useful to add and remove pci device to Xen hypervisor when
>>> load and remove its driver. For example, when VFs are created by PF,
>>> they will be added to Xen hypervisor, and then can be 
>> assigned to guest.
>>> This patch is based on xen-tip-master branch of jeremy's pv-ops tree.
>> Yunhong Jiang sent me a version of this patch as part of his MSI work. 
>> This kind of interception of pci_bus_type.probe is pretty ugly, and is
>> unlikely to be accepted upstream in this form (the patch may only touch
>> a Xen file, but it is changing a variable belonging to the PCI
>> subsystem).  We need to work with the Linux PCI maintainers to 
>> find some
>> other way of achieving what we need here.
>> Can you explain what the functional requirements are here.  Could we
>> defer registering the device with Xen until some other convenient hook,
>> or must it be done at this point in the code?
>> Thanks,
>>    J
> >

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