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
