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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 15/06/13 02:13, Suravee Suthikulanit wrote:
> 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
> > > impersonating
> > > 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
> > > fix.
> > >
> > > In an effort to get AMD systems back to a non-regressed state, 
> > > introduce a
> > > new
> > > 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
> > > correctly.
> > >
> > > Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > Suravee, Jacob,
> >
> > no opinion on this at all? I've been talked into considering this
> > acceptable
> 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
At the very least it can't say BUG -- that needs to be reserved for 
things that actually cause the host to crash (a la BUG_ON()).
 -George


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