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