netdev - Re: [PATCH net-next 00/13] Add mlx5 subfunction support

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Message-ID: <20201119193526.014b968b@kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net>
Date:   Thu, 19 Nov 2020 19:35:26 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Saeed Mahameed <saeed@...nel.org>, Parav Pandit <parav@...dia.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Jiri Pirko <jiri@...dia.com>,
        "dledford@...hat.com" <dledford@...hat.com>,
        Leon Romanovsky <leonro@...dia.com>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [PATCH net-next 00/13] Add mlx5 subfunction support

On Thu, 19 Nov 2020 10:00:17 -0400 Jason Gunthorpe wrote:
> Finally, in the mlx5 model VDPA is just an "application". It asks the
> device to create a 'RDMA' raw ethernet packet QP that is uses rings
> formed in the virtio-net specification. We can create it in the kernel
> using mlx5_vdpa, and we can create it in userspace through the RDMA
> subsystem. Like any "RDMA" application it is contained by the security
> boundary of the PF/VF/SF the mlx5_core is running on.

Thanks for the write up!

The SF part is pretty clear to me, it is what it is. DPDK camp has been
pretty excited about ADI/PASID for a while now.

The part that's blurry to me is VDPA.

I was under the impression that for VDPA the device is supposed to
support native virtio 2.0 (or whatever the "HW friendly" spec was).

I believe that's what the early patches from Intel did.

You're saying it's a client application like any other - do I understand
it right that the hypervisor driver will be translating descriptors
between virtio and device-native then?

The vdpa parent is in the hypervisor correct?

Can a VDPA device have multiple children of the same type?

Why do we have a representor for a SF, if the interface is actually VDPA?
Block and net traffic can't reasonably be treated the same by the switch.

Also I'm confused how block device can bind to mlx5_core - in that case
I'm assuming the QP is bound 1:1 with a QP on the SmartNIC side, and
that QP is plugged into an appropriate backend?