[RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted

[Thiago Jung Bauermann]

Hello,

With Christoph's rework of the DMA API that recently landed, the patch
below is the only change needed in virtio to make it work in a POWER
secure guest under the ultravisor.

The other change we need (making sure the device's dma_map_ops is NULL
so that the dma-direct/swiotlb code is used) can be made in
powerpc-specific code.

Of course, I also have patches (soon to be posted as RFC) which hook up
<linux/mem_encrypt.h> to the powerpc secure guest support code.

What do you think?