On 10/01/2015 12:42 PM, Michael S. Tsirkin wrote: > On Thu, Oct 01, 2015 at 12:22:46PM +0300, Avi Kivity wrote: >> even when they are some users >> prefer to avoid the performance penalty. > I don't think there's a measureable penalty from passing through the > IOMMU, as long as mappings are mostly static (i.e. iommu=pt). I sure > never saw any numbers that show such. >
Maybe not. But again, virtualized setups will not have a guest iommu and therefore can't use it; and those happen to be exactly the setups you're blocking. Non-virtualized setups have an iommu available, but they can also use pci_uio_generic without patching if they like. The virtualized setups have no other option; you're leaving them out in the cold.