In order to reduce needlessly high setup and teardown cost of iotlb mapping during live migration, it's crucial to decouple the vhost-vdpa iotlb abstraction from the virtio device life cycle, i.e. iotlb mappings should be left intact across virtio device reset [1]. For it to work, the on-chip IOMMU parent device should implement a separate .reset_map() operation callback to restore 1:1 DMA mapping without having to resort to the .reset() callback, which is mainly used to reset virtio specific device state. This new .reset_map() callback will be invoked only when the vhost-vdpa driver is to be removed and detached from the vdpa bus, such that other vdpa bus drivers, e.g. virtio-vdpa, can get back on 1:1 DMA mapping when they are attached. For the context, those on-chip IOMMU parent devices, create the 1:1 DMA mapping at vdpa device add, and they would implicitly destroy the 1:1 mapping when the first .set_map or .dma_map callback is invoked. [1] Reducing vdpa migration downtime because of memory pin / maps https://www.mail-archive.com/qemu-devel@xxxxxxxxxx/msg953755.html --- Si-Wei Liu (4): vdpa: introduce .reset_map operation callback vdpa/mlx5: implement .reset_map driver op vhost-vdpa: should restore 1:1 dma mapping before detaching driver vhost-vdpa: introduce IOTLB_PERSIST backend feature bit drivers/vdpa/mlx5/core/mlx5_vdpa.h | 1 + drivers/vdpa/mlx5/core/mr.c | 72 +++++++++++++++++++++----------------- drivers/vdpa/mlx5/net/mlx5_vnet.c | 18 +++++++--- drivers/vhost/vdpa.c | 33 ++++++++++++++++- include/linux/vdpa.h | 7 ++++ include/uapi/linux/vhost_types.h | 2 ++ 6 files changed, 95 insertions(+), 38 deletions(-) -- 1.8.3.1 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
