[vfio-users] IOMMU restrictions inside a VM

[Alex Williamson]

On Mon, 26 Feb 2018 02:12:39 -0500
"Taiidan at gmx.com" <Taiidan at gmx.com> wrote:

> How would I with libvirt/qemu and AMD-Vi v1.26 restrict device 
> communication inside a VM as it would be on the host?

https://libvirt.org/formatdomain.html#elementsIommu

(Yes, you can use Intel IOMMU emulation backed by an AMD IOMMU)

The assigned devices cannot share an IOMMU group with any other
assigned device as we cannot create separate address spaces for devices
which are grouped together.  This configuration will also impose
performance overhead in the DMA mapping path.  You'll need to determine
for your use case if device assignment is sill a performance advantage
vs other options.  The typical use case for emulated IOMMU is isolated
userspace drivers such as DPDK in the guest.  Much like a VM use case,
and unlike a kernel driver use case, these drivers generally use mostly
static mappings for DMA.  Thanks,

Alex