On 09/11/2015 13:15, Michael S. Tsirkin wrote: > Well that's not exactly true. I think we would like to make > it possible to put virtio devices behind an IOMMU on x86, > but if this means existing guests break, then many people won't be able > to use this option: having to find out which kernel version your guest > is running is a significant burden. > > So on the host side, we need to detect guests that > don't program the IOMMU and make QEMU ignore it. > I think we need to figure out a way to do this > before we commit to the guest change. What is the usecase for putting virtio devices behind an IOMMU, apart from: 1) "because you can" 2) using VFIO within the guest ? Case 1 can be ignored, and in case 2 the guest will do the right thing. > Additionally, IOMMU overhead is very high when running within the VM. > So for uses such as VFIO, we'd like a way to make something like > iommu-pt the default. That's not something that the kernel cares about. It's just a configuration issue. Paolo -- 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
