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    SubjectRe: [PATCH 0/4] vdpa: decouple reset of iotlb mapping from device reset
    On Tue, Oct 10, 2023 at 11:05 AM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
    >
    > 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/
    >

    Acked-by: Eugenio Pérez <eperezma@redhat.com>

    Thanks!

    > ---
    > 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(-)
    >
    > --
    > 1.8.3.1
    >

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