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 could implement a separate .reset_map() operation callback to restore 1:1 DMA mapping without having to resort to the .reset() callback, the latter of which is mainly used to reset virtio device state. This new .reset_map() callback will be invoked only before 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 start with 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 creation, and they would implicitly destroy the 1:1 mapping when the first .set_map or .dma_map callback is invoked. This patchset is based off of the descriptor group v3 series from Dragos. [2] [1] Reducing vdpa migration downtime because of memory pin / maps https://www.mail-archive.com/qemu-devel@xxxxxxxxxx/msg953755.html [2] [PATCH vhost v3 00/16] vdpa: Add support for vq descriptor mappings https://lore.kernel.org/lkml/20231009112401.1060447-1-dtatulea@xxxxxxxxxx/ --- v2: - improved commit message to clarify the intended csope of .reset_map API - improved commit messages to clarify no breakage on older userspace v1: - rewrote commit messages to include more detailed description and background - reword to vendor specific IOMMU implementation from on-chip IOMMU - include parent device backend feautres to persistent iotlb precondition - reimplement mlx5_vdpa patch on top of descriptor group series RFC v3: - fix missing return due to merge error in patch #4 RFC v2: - rebased on top of the "[PATCH RFC v2 0/3] vdpa: dedicated descriptor table group" series: https://lore.kernel.org/virtualization/1694248959-13369-1-git-send-email-si-wei.liu@xxxxxxxxxx/ --- Si-Wei Liu (4): vdpa: introduce .reset_map operation callback vhost-vdpa: reset vendor specific mapping to initial state in .release vhost-vdpa: introduce IOTLB_PERSIST backend feature bit vdpa/mlx5: implement .reset_map driver op drivers/vdpa/mlx5/core/mlx5_vdpa.h | 1 + drivers/vdpa/mlx5/core/mr.c | 17 ++++++++++++++++ drivers/vdpa/mlx5/net/mlx5_vnet.c | 18 ++++++++++++----- drivers/vhost/vdpa.c | 31 ++++++++++++++++++++++++++++++ include/linux/vdpa.h | 10 ++++++++++ include/uapi/linux/vhost_types.h | 2 ++ 6 files changed, 74 insertions(+), 5 deletions(-) -- 2.39.3 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
