linux-kernel - Re: [PATCH v2] drivers/virt: vmgenid: add vm generation id driver

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Date:   Fri, 20 Nov 2020 23:29:25 +0100
From:   Jann Horn <jannh@...gle.com>
To:     "Catangiu, Adrian Costin" <acatan@...zon.com>
Cc:     "Graf (AWS), Alexander" <graf@...zon.de>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>, Willy Tarreau <w@....eu>,
        "MacCarthaigh, Colm" <colmmacc@...zon.com>,
        Andy Lutomirski <luto@...nel.org>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Eric Biggers <ebiggers@...nel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        "bonzini@....org" <bonzini@....org>,
        "Singh, Balbir" <sblbir@...zon.com>,
        "Weiss, Radu" <raduweis@...zon.com>,
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Subject: Re: [PATCH v2] drivers/virt: vmgenid: add vm generation id driver

On Mon, Nov 16, 2020 at 4:35 PM Catangiu, Adrian Costin
<acatan@...zon.com> wrote:
> This patch is a driver that exposes a monotonic incremental Virtual
> Machine Generation u32 counter via a char-dev FS interface that
> provides sync and async VmGen counter updates notifications. It also
> provides VmGen counter retrieval and confirmation mechanisms.
>
> The hw provided UUID is not exposed to userspace, it is internally
> used by the driver to keep accounting for the exposed VmGen counter.
> The counter starts from zero when the driver is initialized and
> monotonically increments every time the hw UUID changes (the VM
> generation changes).
>
> On each hw UUID change, the new hypervisor-provided UUID is also fed
> to the kernel RNG.

As for v1:

Is there a reasonable usecase for the "confirmation" mechanism? It
doesn't seem very useful to me.

How do you envision integrating this with libraries that have to work
in restrictive seccomp sandboxes? If this was in the vDSO, that would
be much easier.