linux-kernel - Re: [PATCH v3 00/17] Introducing Linux root partition support for Microsoft Hypervisor

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Message-ID: <20201215164245.yrorpipw2476w35e@liuwe-devbox-debian-v2>
Date:   Tue, 15 Dec 2020 16:42:45 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
Cc:     Wei Liu <wei.liu@...nel.org>,
        Linux on Hyper-V List <linux-hyperv@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        Linux Kernel List <linux-kernel@...r.kernel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Vineeth Pillai <viremana@...ux.microsoft.com>,
        Sunil Muthuswamy <sunilmut@...rosoft.com>,
        Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
        sameo@...ux.intel.com, robert.bradford@...el.com,
        sebastien.boeuf@...el.com
Subject: Re: [PATCH v3 00/17] Introducing Linux root partition support for
 Microsoft Hypervisor

On Tue, Dec 15, 2020 at 04:25:03PM +0100, Enrico Weigelt, metux IT consult wrote:
> On 03.12.20 00:22, Wei Liu wrote:
> 
> Hi,
> 
> > I don't follow. Do you mean reusing /dev/kvm but with a different set of
> > APIs underneath? I don't think that will work.
> 
> My idea was using the same uapi for both hypervisors, so that we can use
> the same userlands for both.
> 
> Are the semantis so different that we can't provide the same API ?

We can provide some similar APIs for ease of porting, but can't provide
1:1 mappings. By definition KVM and MSHV are two different things. There
is no goal to make one ABI / API compatible with the other.

> 
> > In any case, the first version of /dev/mshv was posted a few days ago
> > [0].  While we've chosen to follow closely KVM's model, Microsoft
> > Hypervisor has its own APIs.
> 
> I have to admit, I don't know much about hyperv - what are the main
> differences (from userland perspective) between hyperv and kvm ?
> 

They have different architecture and hence different ways to deal with
things. The difference will inevitably make its way to userland.

Without going into all the details, you can have a look how Xen and KVM
differ architecturally. That will give you a pretty good idea on the
differences.

Wei.

> 
> --mtx
> 
> -- 
> ---
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> Enrico Weigelt, metux IT consult
> Free software and Linux embedded engineering
> info@...ux.net -- +49-151-27565287