RE: [Xen-devel] Handling VT-d translation faults

["Han, Weidong" <weidong.han@xxxxxxxxx>]

Espen Skoglund wrote:
> I've been looking through the VT-d code trying to get a better grip on
> what's going on internally, and I've got some questions regarding VT-d
> translation faults.
> 
>  o Currently all VT-d faults are handled in the iommu_page_fault()
>    handler.  This is kind of a misnomer since the fault handler must
>    also be able to handle interrupt remapping faults and faults
>    related to lookups for the context entry.  I assume that this
>    naming is just temporary?
> 

I agree iommu_page_fault() is kind of a misnomer. 

>  o The fault handler doesn't actually do much right now.  It just
>    clears out the fault queue and prints out warnings.  I can only
>    suspect that some more code to handle faults more gracefully are
>    somewhere in the pipeline.
> 
> The question is what the plans for dealing with DMA translation faults
> are (i.e., due to accessing unmapped memory or writing to read-only
> mappings).  At the very least the associated driver should have the
> possibility to somehow be notified about failed transactions due to
> translation faults.  Is something like this being planned for?
> 

Pls refer to 3.5 setion of VT-d spec. DMA requests that result in
remapping faults must be blocked by hardware. The exact method of DMA
blocking is implementation-specific. Faulting DMA write / read requests
may be handled in much the same way as hardware handles write
requests to non-existent memory. So I think our fault handler that
clears fault queue and prints out warnings is enough.

Randy (Weidong)



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