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

[Wei Wang <wei.wang2@xxxxxxx>]

On 06/08/2012 04:08 PM, Jan Beulich wrote:
> > > > 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).
Yes, probably upstream Linux also has this issue. I will check that. But 
I did not see this issue on 3.2 pv_ops & 2.6 pv_ops.
> 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).
Thanks, I will use PCI_MSI_FLAGS_ENABLE in next post.

Wei

> Jan


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