On Wed, 2014-09-24 at 14:59 -0700, Andy Lutomirski wrote: > Scratch that idea, then. > > The best that I can currently come up with is to say that pre-1.0 > devices on PPC bypass the IOMMU and that 1.0 devices on PPC and all > devices on all other architectures do not bypass the IOMMU. Well, the thing is, we *want* them to bypass the IOMMU for performance reasons in the long run. Today we have no ways to tell our guests that a PCI bus doesn't have an IOMMU, they always do ! Also qemu can mix and match devices on a given PCI bus so making this a bus property wouldn't work either. > I agree that this is far from ideal. Any ideas? Is there any other > channel that QEMU can use to signal to a PPC guest that a specific PCI > virtio device isn't really behind an IOMMU? Any reason why this can't be a virtio capability ? > From my POV, the main > consideration is that existing QEMU versions hosting Xen hypervisors > should work, which is not the case in current kernels, but which is > the case with my patches without any known regressions. > > Is there some evil trick that a PPC guest could use to detect whether > the IOMMU is honored? As an example that I don't like at all, the > guest could program the IOMMU so that the ring's physical address maps > to a second copy of the ring and then see which one works. Cheers, Ben. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
