linux-kernel - Re: [PATCH v5 0/7] vdpa: decouple reset of iotlb mapping from device reset

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Date:   Thu, 26 Oct 2023 03:27:43 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Si-Wei Liu <si-wei.liu@...cle.com>
Cc:     jasowang@...hat.com, eperezma@...hat.com, sgarzare@...hat.com,
        dtatulea@...dia.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/7] vdpa: decouple reset of iotlb mapping from device
 reset

On Thu, Oct 26, 2023 at 12:14:33AM -0700, Si-Wei Liu 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 rebased on top of the latest vhost tree.
> 
> [1] Reducing vdpa migration downtime because of memory pin / maps
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg953755.html


If this is just a squash of v4 with fixes then I already pushed it.
Ignoring this for now.

> ---
> v5:
> - Squashed two fixups to the clean map patch
> 
> v4:
> - Rework compatibility using new .compat_reset driver op
> 
> v3:
> - add .reset_map support to vdpa_sim
> - introduce module parameter to provide bug-for-bug compatibility with older
>   userspace 
> 
> 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 (7):
>   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: introduce .compat_reset operation callback
>   vhost-vdpa: clean iotlb map during reset for older userspace
>   vdpa/mlx5: implement .reset_map driver op
>   vdpa_sim: implement .reset_map support
> 
>  drivers/vdpa/mlx5/core/mlx5_vdpa.h |  1 +
>  drivers/vdpa/mlx5/core/mr.c        | 17 ++++++++++
>  drivers/vdpa/mlx5/net/mlx5_vnet.c  | 27 ++++++++++++++--
>  drivers/vdpa/vdpa_sim/vdpa_sim.c   | 52 ++++++++++++++++++++++++------
>  drivers/vhost/vdpa.c               | 52 +++++++++++++++++++++++++++---
>  drivers/virtio/virtio_vdpa.c       |  2 +-
>  include/linux/vdpa.h               | 30 +++++++++++++++--
>  include/uapi/linux/vhost_types.h   |  2 ++
>  8 files changed, 164 insertions(+), 19 deletions(-)
> 
> -- 
> 2.39.3