Message-ID: <c759c222-34a5-7ee6-933a-457bb98bab81@redhat.com>
Date:   Thu, 11 Nov 2021 09:24:00 +0100
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Subject: Re: [RFC] hypercall-vsock: add a new vsock transport
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To:     "Wang, Wei W" <wei.w.wang@intel.com>,
        Stefano Garzarella <sgarzare@redhat.com>
Cc:     "davem@davemloft.net" <davem@davemloft.net>,
        "kuba@kernel.org" <kuba@kernel.org>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        "mst@redhat.com" <mst@redhat.com>,
        "kys@microsoft.com" <kys@microsoft.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "virtualization@lists.linux-foundation.org" 
        <virtualization@lists.linux-foundation.org>,
        "Yamahata, Isaku" <isaku.yamahata@intel.com>,
        "Nakajima, Jun" <jun.nakajima@intel.com>,
        "Kleen, Andi" <andi.kleen@intel.com>,
        Andra Paraschiv <andraprs@amazon.com>,
        Sergio Lopez Pascual <slp@redhat.com>
References: <71d7b0463629471e9d4887d7fcef1d8d@intel.com>
 <20211110111718.5cvt6vgory3fzqld@steredhat>
 <9901a74b149d4245b0e6c998b5cde7af@intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <9901a74b149d4245b0e6c998b5cde7af@intel.com>
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Precedence: bulk

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