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Re: [Xen-devel] [PATCH v3] AMD/intremap: Prevent use of per-device vector maps until irq logic is fixed

On 6/10/2013 7:25 AM, Jan Beulich wrote:
On 04.06.13 at 18:38, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
XSA-36 changed the default vector map mode from global to per-device.  This is
because a global vector map does not prevent one PCI device from
another and launching a DoS on the system.

However, the per-device vector map logic is broken for devices with multiple
MSI-X vectors, which can either result in a failed ASSERT() or misprogramming
of a guests interrupt remapping tables.  The core problem is not trivial to

In an effort to get AMD systems back to a non-regressed state, introduce a
type of vector map called per-device-global.  This uses per-device vector maps
in the IOMMU, but uses a single used_vector map for the core IRQ logic.

This patch is intended to be removed as soon as the per-device logic is fixed

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Suravee, Jacob,

no opinion on this at all? I've been talked into considering this

Sorry for late reply, and for having missed this conversation previously.

If we have to go with this solution temporary until we have the permanent fix.
I think that is okay with me.  Although, would you mind pointing out the affect
of having "per-device" vs. "global" irq vector map?  I am not quite familiar
with the differences.

(with a small coding style fixup, and with the question on
the usefulness of the final warning message - imo redundant with the
immediately preceding message that is being left untouched)

I also think the messages are quite confusing.  Actually, now that we can have
irq vector map and intremap map with different mode, we should be more explicit
in the message.

Also, the message "Not overriding irq_vector_map setting" is confusing to me.

Would you mind considering the attached patch?  Here is the sample output

(XEN) AMD-Vi: IOMMU 0 Enabled.
(XEN) AMD-Vi BUG: per-device vector map logic is broken.  Using 
per-device-global maps instead until a fix is found
(XEN) AMD-Vi: Enabling global irq vector map
(XEN) AMD-Vi: Enabling per-device interrupt remap table.

Thank you,


Attachment: AMD-intremap-Prevent-use-of-per-device-vector-maps-V4.patch
Description: AMD-intremap-Prevent-use-of-per-device-vector-maps-V4.patch

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