From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alex Williamson <alex.williamson@redhat.com>
Subject: Re: VFIO no-iommu
Date: Fri, 11 Dec 2015 16:02:33 -0700
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To: Vincent JARDIN <vincent.jardin@6wind.com>, dev@dpdk.org
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On Fri, 2015-12-11 at 23:12 +0100, Vincent JARDIN wrote:
> Thanks Thomas for putting back this topic.
>=20
> Alex,
>=20
> 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=3D033291eccbdb1b70ffc02641edae19ac825dc75d
> =C2=A0=C2=A0=C2=A0Use of this mode, specifically binding a device witho=
ut a native
> =C2=A0=C2=A0=C2=A0IOMMU group to a VFIO bus driver will taint the kerne=
l and should
> =C2=A0=C2=A0=C2=A0therefore not be considered supported.
>=20
> It means that we get ride of uio; so it is a nice code cleanup: but
> why=20
> would VFIO/NO IOMMU be better if the bottomline is "unsupported"?

How supportable do you think the uio method is? =C2=A0Fundamentally we ha=
ve
a userspace driver doing unrestricted DMA; it can access and modify any
memory in the system. =C2=A0This is the reason uio won't provide a mechan=
ism
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.
=C2=A0Unless we can sandbox a user owned device within an IOMMU protected
container, it's not supportable. =C2=A0The 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. =C2=A0Thanks,

Alex