[PATCH 0/3] Fix virtio-blk issue with SWIOTLB

[Joerg Roedel <joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>]

Hi,

there is a problem with virtio-blk driven devices when
virtio-ring uses SWIOTLB through the DMA-API. This happens
for example in AMD-SEV enabled guests, where the guest RAM
is mostly encrypted and all emulated DMA has to happen
to/from the SWIOTLB aperture.

The problem is a limitation of the SWIOTLB implementation,
which does not support allocations larger than 256kb. When
the virtio-blk driver tries to read/write a block larger
than that, the allocation of the dma-handle fails and an IO
error is reported.

This patch-set adds a check to the virtio-code whether it
might be using SWIOTLB bounce buffering and limits the
maximum segment size in the virtio-blk driver in this case,
so that it doesn't try to do larger reads/writes.

Please review.

Thanks,

	Joerg

Joerg Roedel (3):
  swiotlb: Export maximum allocation size
  virtio: Introduce virtio_max_dma_size()
  virtio-blk: Consider virtio_max_dma_size() for maximum segment size

 drivers/block/virtio_blk.c   | 10 ++++++----
 drivers/virtio/virtio_ring.c | 11 +++++++++++
 include/linux/swiotlb.h      | 12 ++++++++++++
 include/linux/virtio.h       |  2 ++
 4 files changed, 31 insertions(+), 4 deletions(-)

-- 
2.17.1