On Tue, Aug 07, 2018 at 12:46:34AM +0300, Michael S. Tsirkin wrote:

Well we have the RFC for that - the switch to using DMA ops unconditionally isn't
problematic itself IMHO, for now that RFC is blocked
by its perfromance overhead for now but Christoph says
he's trying to remove that for direct mappings,
so we should hopefully be able to get there in X weeks.

The direct calls to dma_direct_ops aren't going to help you with legacy
virtio, given that virtio is specified to deal with physical addresses,
while dma-direct is not in many cases.

It would however help with the case where qemu always sets the platform
dma flag, as we'd avoid the indirect calls for that.