linux-kernel - Re: [PATCH v2 13/15] uapi: hyperv: Add mshv driver headers hvhdk.h, hvhdk_mini.h, hvgdk.h, hvgdk

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Message-ID: <c4482a6a-aed0-4750-aa1b-421f0e541cfa@linux.microsoft.com>
Date:   Fri, 25 Aug 2023 11:24:58 -0700
From:   Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To:     Greg KH <gregkh@...uxfoundation.org>, Wei Liu <wei.liu@...nel.org>
Cc:     linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arch@...r.kernel.org, patches@...ts.linux.dev,
        mikelley@...rosoft.com, kys@...rosoft.com, haiyangz@...rosoft.com,
        decui@...rosoft.com, apais@...ux.microsoft.com,
        Tianyu.Lan@...rosoft.com, ssengar@...ux.microsoft.com,
        mukeshrathor@...rosoft.com, stanislav.kinsburskiy@...il.com,
        jinankjain@...ux.microsoft.com, vkuznets@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, will@...nel.org,
        catalin.marinas@....com
Subject: Re: [PATCH v2 13/15] uapi: hyperv: Add mshv driver headers hvhdk.h,
 hvhdk_mini.h, hvgdk.h, hvgdk_mini.h

On 8/19/2023 3:26 AM, Greg KH wrote:
> 
> My "strong" opinion is the one kernel development rule that we have,
> "you can not break userspace".  So, if you change these
> values/structures/whatever in the future, and userspace tools break,
> that's not ok and the changes have to be reverted.
> 
> If you can control both sides of the API here (with open tools that you
> can guarantee everyone will always update to), then yes, you can change
> the api in the future.
> 

This is true for us - we contribute and maintain support for this driver
in Cloud Hypervisor[1], an open source VMM.

We also do a check of the hypervisor version when the driver loads, and
refuse to proceed if it is running on an incompatible hypervisor.

Thanks,
Nuno Das Neves


[1] https://github.com/cloud-hypervisor/cloud-hypervisor