On Tue, Nov 03, 2015 at 10:08:13AM +1100, Benjamin Herrenschmidt wrote: > On Mon, 2015-11-02 at 22:45 +0100, Arnd Bergmann wrote: > > > Then I would argue for naming this differently. Make it an optional > > > hint "DMA_ATTR_HIGH_PERF" or something like that. Whether this is > > > achieved via using a bypass or other means in the backend not the > > > business of the driver. > > > > > > > With a name like that, who wouldn't pass that flag? ;-) > > xHCI for example, vs. something like 10G ethernet... but yes I agree it > sucks. I don't like that sort of policy anywhere in drivers. On the > other hand the platform doesn't have much information to make that sort > of decision either. Mabye because it should simply use what's optimal? E.g. passthrough whenever possible, where arguments against possible are: dma_mask, vfio requirements, kernel command line option. This is what a lot of architectures already do, I remember the SGI Origin / Altix code has the same behavior as well. Those IOMMUs already had the 64 bit passthrough and 32-bit sliding window in addition to the real IOMMU 10 years ago. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
