Re: [Xen-devel] [PATCH] amd iommu: re-enable iommu msi if dom0 disabled it

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.06.12 at 15:41, Wei Wang <wei.wang2@xxxxxxx> wrote:
> On 06/08/2012 03:31 PM, Andrew Cooper wrote:
>> On 08/06/12 14:28, Wei Wang wrote:
>>> I found that recent dom0 (e.g 3.4 pv_ops) disables iommu msi capability
>>> for some reasons and iommu cannot generate any interrupts in this case.
>>> Attached patch re-enables it in device assignment.
>>
>> Under which circumstances should dom0 able to play with the IOMMUs ?
>> Surely the fact that dom0 can play with the IOMMUs is a bug in itself.
> 
> It looks like some generic msi/pci codes disable it, not the Linux iommu 
> driver itself, which is only loaded on bare metal. AMD IOMMU expose 
> interrupt capability as a normal msi block. So the general pci/msi layer 
> of dom0 might touch it...

In that case it wouldn't be on pv-ops alone (which your patch
says).

Also, your patch using IOMMU_CONTROL_ENABLED instead of
PCI_MSI_FLAGS_ENABLE is quite misleading (as it hides the fact
the what you play with is not IOMMU-specific).

Jan


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