linux-kernel - [PATCH RFC 0/4] vdpa: decouple reset of iotlb mapping from device reset

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Date:   Mon, 14 Aug 2023 18:43:23 -0700
From:   Si-Wei Liu <si-wei.liu@...cle.com>
To:     jasowang@...hat.com
Cc:     eperezma@...hat.com, gal@...dia.com, linux-kernel@...r.kernel.org,
        mst@...hat.com, si-wei.liu@...cle.com,
        virtualization@...ts.linux-foundation.org,
        xuanzhuo@...ux.alibaba.com
Subject: [PATCH RFC 0/4] vdpa: decouple reset of iotlb mapping from device reset

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@nongnu.org/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