linux-kernel - Re: [PATCH 09/16] vdpa/mlx5: Allow creation/deletion of any given mr struct

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Date:   Tue, 26 Sep 2023 12:44:43 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Dragos Tatulea <dtatulea@...dia.com>
Cc:     Eugenio Pérez <eperezma@...hat.com>,
        Si-Wei Liu <si-wei.liu@...cle.com>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, Parav Pandit <parav@...dia.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, kvm@...r.kernel.org
Subject: Re: [PATCH 09/16] vdpa/mlx5: Allow creation/deletion of any given mr struct

On Tue, Sep 12, 2023 at 9:02 PM Dragos Tatulea <dtatulea@...dia.com> wrote:
>
> This patch adapts the mr creation/deletion code to be able to work with
> any given mr struct pointer. All the APIs are adapted to take an extra
> parameter for the mr.
>
> mlx5_vdpa_create/delete_mr doesn't need a ASID parameter anymore. The
> check is done in the caller instead (mlx5_set_map).
>
> This change is needed for a followup patch which will introduce an
> additional mr for the vq descriptor data.
>
> Signed-off-by: Dragos Tatulea <dtatulea@...dia.com>
> ---

Thinking of this decoupling I think I have a question.

We advertise 2 address spaces and 2 groups. So we actually don't know
for example which address spaces will be used by dvq.

And actually we allow the user space to do something like

set_group_asid(dvq_group, 0)
set_map(0)
set_group_asid(dvq_group, 1)
set_map(1)

I wonder if the decoupling like this patch can work and why.

It looks to me the most easy way is to let each AS be backed by an MR.
Then we don't even need to care about the dvq, cvq.

Thanks