[+cc Alex] On Tue, May 22, 2018 at 02:09:59PM -0700, Doug Meyer wrote: > Logan answered the questions quite thoroughly. (Thanks, Logan!) When you repost it, please rework the commit log so it answers the questions directly. Otherwise the next reader may have the same questions again. E.g., say something about how the proxy IDs are not programmable and are fixed in the hardware so all we have to do is read them. I don't think the question of when the aliases need to be added is quite closed. Logan said "it seems pci_add_dma_alias() must be called before the driver is initialized and therefore in a quirk", but that doesn't make clear *why* the alias needs to be added before the driver is initialized. The alias shouldn't be needed until the device does a DMA, and it shouldn't do that until after the driver initializes. I suspect the reason the existing quirks are in drivers/pci/quirks.c is because the IOMMU driver is in the host OS, but the host may not have a driver for the device if the device is passed through to a guest OS. In that case, the only way to add the alias is by using a quirk that is always built into the host OS. We could argue that the driver in the guest should be able to tell the host's IOMMU driver about these aliases, but I doubt there's an interface for that. Bjorn
