[dpdk-dev] VFIO no-iommu

[Alex Williamson]

On Fri, 2015-12-11 at 23:12 +0100, Vincent JARDIN wrote:
> Thanks Thomas for putting back this topic.
> 
> Alex,
> 
> I'd like to hear more about the impacts of "unsupported":
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commi
> t/?id=033291eccbdb1b70ffc02641edae19ac825dc75d
>    Use of this mode, specifically binding a device without a native
>    IOMMU group to a VFIO bus driver will taint the kernel and should
>    therefore not be considered supported.
> 
> It means that we get ride of uio; so it is a nice code cleanup: but
> why 
> would VFIO/NO IOMMU be better if the bottomline is "unsupported"?

How supportable do you think the uio method is?  Fundamentally we have
a userspace driver doing unrestricted DMA; it can access and modify any
memory in the system.  This is the reason uio won't provide a mechanism
to enable MSI and if you ask the uio maintainer, they don't support DMA
at all, it's only intended as a programmed IO interface to the device.
 Unless we can sandbox a user owned device within an IOMMU protected
container, it's not supportable.  The VFIO no-iommu mode can simply
provide you that unsupported mode more easily since it leverages code
from the supported mode, which is IOMMU protected.  Thanks,

Alex