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 07:21:43 +0000
From:   Dragos Tatulea <dtatulea@...dia.com>
To:     "jasowang@...hat.com" <jasowang@...hat.com>
CC:     "xuanzhuo@...ux.alibaba.com" <xuanzhuo@...ux.alibaba.com>,
        Parav Pandit <parav@...dia.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "eperezma@...hat.com" <eperezma@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "si-wei.liu@...cle.com" <si-wei.liu@...cle.com>,
        "mst@...hat.com" <mst@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [PATCH 09/16] vdpa/mlx5: Allow creation/deletion of any given mr
 struct

On Tue, 2023-09-26 at 12:44 +0800, Jason Wang wrote:
> 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.
> 
This scenario could indeed work. Especially if you look at the 13'th patch [0]
where hw support is added. Are you wondering if this should work at all or if it
should be blocked?

> 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.
That's what this patch series dowes.

Thanks,
Dragos

[0]https://lore.kernel.org/virtualization/20230912130132.561193-14-dtatulea@nvidia.com/T/#u