to the kdump kernel with as little
    code as we can, so shutting down drivers properly is not an option.

    The workaround is to add 'machvec=dig' to the kdump kernel boot parameters.
    This makes the kdump kernel avoid using the sba iommu altogether, leaving
    the IOTLB intact.  Any ongoing DMA falls harmlessly outside the kdump
    kernel.  After the kdump kernel reboots, all devices will have been
    shutdown properly and DMA stopped.

This patch pushes that functionality into the sba iommu initialization
code, so that users won't have to find the obscure documentation telling
them about 'machvec=dig'.

This means that also for hpzx1 it's not possible to boot when all
memory is above the 4 GB limit. So the only machine vectors that can handle
this case are "sn2" and "uv".

Signed-off-by: Bernhard Walle <bwalle@suse.de>
Signed-off-by: Tony Luck <tony.luck@intel.com>
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