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This is necessary so that > > > preserved devices can DMA through the IOMMU during a Live Update > > > (changing bus numbers would break IOMMU translation). > > > > I think changing bus numbers would break DMA regardless of whether an > > IOMMU is involved. Completions carrying the data for DMA reads are > > routed back to the Requester ID of the read. > > Ahh, makes sense. I'll clarify the commit message in the next > version. More broadly you can't shouldn't the fabric topology while Memory Enable is active. Renumbering or readdressing the fabric requires disabling and flushing any memory transactions. >From that reasoning it is clearer that you can't do that if the device is expected to hitlesslly continue performing memory operations. That may be a clearer long term basis for describing the requirements here. Jason