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Subject[PATCH v2 0/4] vdpa: decouple reset of iotlb mapping from device reset
Date
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@nongnu.org/msg953755.html
[2] [PATCH vhost v3 00/16] vdpa: Add support for vq descriptor mappings
https://lore.kernel.org/lkml/20231009112401.1060447-1-dtatulea@nvidia.com/

---
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@oracle.com/

---

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

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