Re: [Xen-devel] [PATCH] xen/mcfg: Call PHYSDEVOP_pci_mmcfg_reserved before PCI enumeration

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.09.15 at 16:09, <konrad.wilk@xxxxxxxxxx> wrote:
> On Tue, Sep 22, 2015 at 07:57:29AM -0600, Jan Beulich wrote:
>> >>> On 22.09.15 at 15:36, <konrad.wilk@xxxxxxxxxx> wrote:
>> > The best I could come up with is to do two loops:
>> >  1) for 0:0:0 -> ff:ff:ff call PHYSDEVOP_pci_device_remove
>> >     (so blow away what Xen has for its PCI devices.. except for the AMD 
>> > IOMMU)
>> >  2) list_for_each_pci_device PHYSDEVOP_pci_device_add (or other variants
>> >     if VF).
>> > 
>> > But that is just a hack working around the Linux code.
>> 
>> The price of being non-intrusive on the Linux side. The above would
>> seem okay to me for the (rare?) reassign case. (Not sure why you
>> mean to exclude the AMD IOMMU there.)
> 
> I think we hide it altogether from the dom0 - so when it does the
> bus reassignment it does not see the AMD IOMMU.
> 
> My concern was that the bus number of the AMD IOMMU device may
> overlap with other bus numbers - which got moved as a result
> of the bridge expanding its subordinate bus numbers.
> 
> In other words, the AMD IOMMU may have been at bus 0xb, the
> bridge in question at 0x01, with an PCI device at 0x02;
> some devices between 0x03 down to 0x0a.
> 
> The bridge would now cover 0x01->0x04 (with the PCI device
> still at 0x02). But the devices at the old 0x03->0x0a have now
> been shifted to 0x04->0x0b. And the AMD IOMMU is at 0x0c.
> 
> But Xen has no clue about this and "loses" the AMD IOMMU and
> starts writting configuration data to whatever poor device used to
> be at bus 0x0b.

And how would that issue be solved by leaving that device alone?

Jan


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