On Fri, 2014-09-05 at 12:01 +0930, Rusty Russell wrote: > If the answers are both "yes", then x86 is going to be able to use > virtio+IOMMU, so PPC looks like the odd one out. Well, yes and no ... ppc will be able to do that too, it's just pointless and will suck performances. Additionally, it will be incompatible with existing guests since today, the guest assumes physical (doesn't use the dma mapping routines), so even if x86 grows the ability to have virtio behind an iommu in qemu, that will break existing guests. > Otherwise it looks > like we're really going to want to stick with the "ignore IOMMU" rule > until (handwave future), and we make an exception for Xen. Either that or we have a capability that can be negociated. There are other reasons for wanting to allow the use of the DMA ops, such as people using virtio as a transport between two physically connected machines (such as a CPU running a PCIe endpoint to a CPU running a PCIe host, or two hosts connected to a non-transparent switch, essentially using PCIe as a fast network fabric). Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
