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

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Message-ID: <CAJaqyWfnDXUPZz8Gb=Bkw2CB=w11KCsyT6YWp92GumNwz5_gQw@mail.gmail.com>
Date:   Wed, 11 Oct 2023 13:30:10 +0200
From:   Eugenio Perez Martin <eperezma@...hat.com>
To:     Si-Wei Liu <si-wei.liu@...cle.com>
Cc:     jasowang@...hat.com, mst@...hat.com, xuanzhuo@...ux.alibaba.com,
        dtatulea@...dia.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [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@...cle.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@...hat.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
>