On Thu, Feb 20, 2020 at 05:06:04PM +0100, Halil Pasic wrote: > For vhost-net the feature VIRTIO_F_IOMMU_PLATFORM has the following side > effect The vhost code assumes it the addresses on the virtio descriptor > ring are not guest physical addresses but iova's, and insists on doing a > translation of these regardless of what transport is used (e.g. whether > we emulate a PCI or a CCW device). (For details see commit 6b1e6cc7855b > "vhost: new device IOTLB API".) On s390 this results in severe > performance degradation (c.a. factor 10). BTW with ccw I/O there is > (architecturally) no IOMMU, so the whole address translation makes no > sense in the context of virtio-ccw. So it sounds like a host issue: the emulation of s390 unnecessarily complicated. Working around it by the guest looks wrong ... > Halil Pasic (2): > mm: move force_dma_unencrypted() to mem_encrypt.h > virtio: let virtio use DMA API when guest RAM is protected > > drivers/virtio/virtio_ring.c | 3 +++ > include/linux/dma-direct.h | 9 --------- > include/linux/mem_encrypt.h | 10 ++++++++++ > 3 files changed, 13 insertions(+), 9 deletions(-) > > > base-commit: ca7e1fd1026c5af6a533b4b5447e1d2f153e28f2 > -- > 2.17.1
