Re: [Xen-devel] Xen 4.2.1 boot failure with IOMMU enabled

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.02.13 at 02:33, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote:
> I am wondering whether such cases (undeclared devices in IVRS) should cause 
> a panic or disabling of IOMMU. This may be a more generic case of Jan's 
> earlier 
> patch for dealing with missing IOAPIC. Not sure whether it would be possible 
> to "unwind" IOMMU at this point though.

I doubt it - this would likely cause further problems down the road.

Instead, with us doing a bus scan anyway (as of 4.1), we could
detect the problem much earlier (and only bug on devices that we
don't find but Dom0 does - in particular, I'm wondering how SR-IOV
VFs would get dealt with here).

Furthermore I wonder whether in the single IOMMU case we
couldn't deal with this on the same basis as is being done (sort of
unintendedly) for the IO-APIC case: The single IOMMU in the
system _must_ be the one responsible for any device not reported
by the firmware. That would deal with povder's case, and
experience tells us that more complex (read: expensive) systems
tend to have less ACPI table flaws (i.e. wouldn't suffer from not
being covered by such a workaround).

Jan


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