Re: [Xen-devel] [PATCH V2] amd iommu: re-enable iommu msi if dom0 disabled it

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.06.12 at 14:02, Wei Wang <wei.wang2@xxxxxxx> wrote:
> I had attached a revised patch, please check it.

While the patch technically looks better now, you didn't eliminate
my objections to the approach you take, nor did you comment on
the proposed alternative.

A fundamental problem is that your IOMMUs show up as a "normal"
PCI devices, breaking the separation between what is being
managed by the hypervisor vs by the Dom0 kernel. (This even
allows something as odd as passing through an IOMMU to a
DomU, which would clearly upset the hypervisor.)

> I found that the following Linux commit triggers this issue. It has been 
> included into 3.4 pv_ops.
> 
> " commit a776c491ca5e38c26d9f66923ff574d041e747f4
>    Author: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
>    Date:   Mon Oct 17 11:46:06 2011 -0700
> 
>    PCI: msi: Disable msi interrupts when we initialize a pci device "

Thanks for locating this. As it stands, it is incomplete though
anyway: If the kexec-ed kernel is one built without CONFIG_PCI_MSI,
it won't have a means to suppress the "screaming" interrupts.

Jan


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