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

[Jason Wang]

On 2019/1/10 äå9:44, Joerg Roedel wrote:
> 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.


Just wonder if my understanding is correct IOMMU_PLATFORM must be set 
for all virtio devices under AMD-SEV guests?

Thanks


> 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(-)