Pull VT-d hardware workarounds from David Woodhouse:
"This contains a workaround for hardware issues which I *thought* were
never going to be seen on production hardware. I'm glad I checked
that before the 4.1 release...
Firstly, PASID support is so broken on existing chips that we're just
going to declare the old capability bit 28 as 'reserved' and change
the VT-d spec to move PASID support to another bit. So any existing
hardware doesn't support SVM; it only sets that (now) meaningless bit
28.
That patch *wasn't* imperative for 4.1 because we don't have PASID
support yet. But *even* the extended context tables are broken — if
you just enable the wider tables and use none of the new bits in them,
which is precisely what 4.1 does, you find that translations don't
work. It's this problem which I thought was caught in time to be
fixed before production, but wasn't.
To avoid triggering this issue, we now *only* enable the extended
context tables on hardware which also advertises "we have PASID
support and we actually tested it this time" with the new PASID
feature bit.
In addition, I've added an 'intel_iommu=ecs_off' command line
parameter to allow us to disable it manually if we need to"
* git://git.infradead.org/intel-iommu:
iommu/vt-d: Only enable extended context tables if PASID is supported
iommu/vt-d: Change PASID support to bit 40 of Extended Capability Register
