linux-kernel - Re: [RFC] hypercall-vsock: add a new vsock transport

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Date:   Thu, 11 Nov 2021 09:24:00 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Wang, Wei W" <wei.w.wang@...el.com>,
        Stefano Garzarella <sgarzare@...hat.com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "mst@...hat.com" <mst@...hat.com>,
        "kys@...rosoft.com" <kys@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "Nakajima, Jun" <jun.nakajima@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>,
        Andra Paraschiv <andraprs@...zon.com>,
        Sergio Lopez Pascual <slp@...hat.com>
Subject: Re: [RFC] hypercall-vsock: add a new vsock transport

On 11/11/21 09:14, Wang, Wei W wrote:
>> Adding Andra and Sergio, because IIRC Firecracker and libkrun 
>> emulates virtio-vsock with virtio-mmio so the implementation
>> should be simple and also not directly tied to a specific VMM.
>> 
> OK. This would be OK for KVM based guests. For Hyperv and VMWare 
> based guests, they don't have virtio-mmio support. If the MigTD (a 
> special guest) we provide is based on virtio-mmio, it would not be 
> usable to them.

Hyper-V and VMware (and KVM) would have to add support for
hypercall-vsock anyway.  Why can't they just implement a subset of
virtio-mmio?  It's not hard and there's even plenty of permissively-
licensed code in the various VMMs for the *BSDs.

In fact, instead of defining your own transport for vsock, my first idea
would have been the opposite: reuse virtio-mmio for the registers and
the virtqueue format, and define your own virtio device for the MigTD!

Thanks,

Paolo