[Kata-hypervisor] Link to the Hypervisor Prototype

Jessie Frazelle (TUPPERWARE) jessfraz at microsoft.com
Thu Jun 7 02:04:57 UTC 2018


I'm not convinced by 9p

Also I don't think a cloud native VMM or anything like that is the answer... But I'm a huge fan of being able to run things on bare metal or my desktop :P

In my ideal scenario it would be the bare minimum needed and also not have anything that required backwards compat to old kernels.. because why..

Anyways if you all are interested and/or have time or resources... I'd love to collect ideas :) you all have a great deal of experience in this area and I think it's a cool opportunity to build something minimal, secure and fast.


________________________________________
From: Anthony Liguori <aliguori at amazon.com>
Sent: Wednesday, June 6, 2018 8:50:43 PM
To: Jon Olson
Cc: Jessie Frazelle (TUPPERWARE); Ernst, Eric; Sasha Levin; Manohar Castelino; kata-hypervisor at lists.katacontainers.io
Subject: Re: [Kata-hypervisor] Link to the Hypervisor Prototype

Jon Olson <jonolson at google.com> writes:

> (note: currently at an off-site: responses may be delayed or worse)
>
> The interest that I had (and at the risk of speaking for him and being
> corrected, I think Ben as well) was in a VM *shape* focussed on something
> suitable for containers. In particular something based on a modern set of
> hardware features and minimizing the need for emulation of anything (PITs,
> PICs, PCI controllers, etc.)

I get what you're after but I've grown to believe it's not the right
thing.

You really want to present an APIC because then you get APIC-V and
Posted Interrupts.  This is the path Xen went with PV and it's boxed
them into a corner where not only are event channels far worse than
APIC-based delivery (they are inherently unfair) but now you don't get
the performance boost that comes from Posted Interrupts due to that
feature.

PCI is really not that bad at all to emulate and you have to do
discovery in some way.  Again, lots of bad examples here (Xenstore for
instance) but I don't mean to pick on Xen here.

The complexity of emulation is not so bad.  Part of what explodes QEMU
in terms of complexity is the backend implementations.  Once you need to
support VMDK and QCOW2, you've got a massive code base.

I know why folks want v9fs too but man that's a complex protocol and
mapping it to POSIX is very complex.  The legacy device emulation is the
least of your concerns IMHO.

> I would agree that for what qemu does that it's hard to do better, but
> we're actively uninterested in many of the things qemu does being supported
> by our offering. They don't help workloads we care about and they present
> "challenging" surface areas from a security perspective.
>
> Note that Google does actually have such a VM, aimed at containers and open
> source, implemented in Rust for Chrome OS. We are not using it in Cloud
> currently (and to be honest I haven't dived into it beyond being highly
> amused at the horrifying kernel command line that explicitly MMIO maps app
> of their virtio devices). This was on a production Pixel book, so nothing
> fancy or proprietary going on there.

I like crosvm and have looked at the code pretty deeply.  It actually
has a bit of legacy emulation but it's naive in approach to it.  I'm not
sure splitting the device model into a separate process is the right
approach but I like the fact that it's at least doing something different.

I think if you are going to do legacy emulation, you need to do it right
and completely.  You can get stuff booting with a UART that turns a THR
write into a putchar() call but ultimately, you need to implement FIFO
and flow control properly.

Almost every device model in QEMU started out as a bare bones minimum
function model but grew over time because of need into what it is today.

Regards,

Anthony Liguori

>
> Jon
>
> On Wed, Jun 6, 2018, 4:14 PM Anthony Liguori <aliguori at amazon.com> wrote:
>
>> "Jessie Frazelle (TUPPERWARE)" <jessfraz at microsoft.com> writes:
>>
>> > Sorry outlook cut off the first line... windows...
>> >
>> > so rust :D
>>
>> I was able to join the prep call at least and I raised this during that
>> discussion.  I'm not sure what problem this group is trying to tackle.
>>
>> What was brought up on the call is a "cloud VMM" as an alternative to
>> QEMU but I don't really agree with that premise.  For the problem space
>> that QEMU tackles, it's hard to do better than it does and it tackles a
>> huge space.
>>
>> Cloud is an extremely ambiguous term too.  In another part of this
>> thread, qcow2 was mentioned as a target which I don't think at all is
>> something that is interesting if you are an infrastructure provider.
>>
>> There's lot of stuff that I am interested in (particularly around super
>> fast start up time and super low overhead to get high density) but
>> that's only possible to achieve if you constrain the problem space
>> tremendously.
>>
>> Regards,
>>
>> Anthony Liguori
>>
>> >
>> > ________________________________________
>> > From: Jessie Frazelle (TUPPERWARE) <jessfraz at microsoft.com>
>> > Sent: Wednesday, June 6, 2018 6:37 PM
>> > To: Anthony Liguori; Ernst, Eric; Sasha Levin; Manohar Castelino
>> > Cc: kata-hypervisor at lists.katacontainers.io
>> > Subject: Re: [Kata-hypervisor] Link to the Hypervisor Prototype
>> >
>> > Rust?
>> >
>> > What would you do?
>> >
>> > ________________________________________
>> > From: Anthony Liguori <aliguori at amazon.com>
>> > Sent: Wednesday, June 6, 2018 6:36 PM
>> > To: Jessie Frazelle (TUPPERWARE); Ernst, Eric; Sasha Levin; Manohar
>> Castelino
>> > Cc: kata-hypervisor at lists.katacontainers.io
>> > Subject: Re: [Kata-hypervisor] Link to the Hypervisor Prototype
>> >
>> > "Jessie Frazelle (TUPPERWARE)" <jessfraz at microsoft.com> writes:
>> >
>> >> Anthony,
>> >>
>> >> Would you be willing to dedicate resources to a _hypothetical_ rewrite
>> >> of that layer that we could replace qemu with in the form of a go
>> >> library?
>> >>
>> >> 0:)
>> >
>> > Go is so 2015.  Rust is where it's at now :-)
>> >
>> > In all seriousness, I've always felt strongly that a device model needs
>> > to avoid garbage collection.  While it's not strictly a real time
>> > system, OSes have an expectation that PIO or MMIO operations have an
>> > upper bound of latency.
>> >
>> > The other challenge with Go is unpredictable memory usage due to
>> > automatic heap growth.  If you want to do planning around density, being
>> > able to rationalize about the memory overhead from the VMM layer is
>> > pretty important.
>> >
>> > Regards,
>> >
>> > Anthony Liguori
>> >
>> >>
>> >>
>> >>
>> >> ________________________________________
>> >> From: Anthony Liguori <aliguori at amazon.com>
>> >> Sent: Wednesday, June 6, 2018 5:00 PM
>> >> To: Ernst, Eric; Sasha Levin; Manohar Castelino
>> >> Cc: kata-hypervisor at lists.katacontainers.io
>> >> Subject: Re: [Kata-hypervisor] Link to the Hypervisor Prototype
>> >>
>> >> "Ernst, Eric" <eric.ernst at intel.com> writes:
>> >>
>> >>> Hey Sasha, Anthony –
>> >>>
>> >>> I want to set a bit of context here.  At the face to face discussion
>> >>> in Vancouver, we had agreed to share the prototyping we have put in
>> >>> place to better understand how far we could go to remove legacy, and
>> >>> minimize the number of device models, while still booting key
>> >>> workloads.  Manohar’s response is to address the action that everyone
>> >>> in the meeting requested.
>> >>
>> >> Yup, appreciate the sharing and am disappointed I wasn't able to attend
>> >> in person.  I'm sure Paolo gave you lots of great feedback but let me
>> >> expand a bit on why I think this is the wrong approach.  Ultimately, you
>> >> are certainly free to continue down this path though but just thought
>> >> you may find this useful.
>> >>
>> >> The pieces of QEMU that are easy to remove are largely already
>> >> configurable at build time.  From a practical perspective, if you build
>> >> your "prototype" and measure the resulting executable size compared to a
>> >> minimalistic configuration, you will find very little actual reduction
>> >> in code.
>> >>
>> >> The stuff that's hard to remove is deeply ingrained (like QMP and QOM)
>> >> or parts that are just hairy (like vl.c).  Years of effort have gone
>> >> into decoupling these bits.
>> >>
>> >> So you get very little actual benefit (in code size reduction) by
>> >> forking but get to bare the burden of independent maintenance.
>> >>
>> >> Regards,
>> >>
>> >> Anthony Liguori
>> >>
>> >>
>> >>>
>> >>> Cheers,
>> >>> Eric
>> >>>
>> >>> On 6/6/18, 1:46 PM, "Sasha Levin" <Alexander.Levin at microsoft.com>
>> wrote:
>> >>>
>> >>>     On Wed, Jun 06, 2018 at 08:08:46PM +0000, Castelino, Manohar R
>> wrote:
>> >>>     >Folks,
>> >>>     >
>> >>>     >Please find below the link to the initial prototype code that
>> tries to reduce the number of emulated devices in QEMU that can still boot
>> most cloud workloads.
>> >>>     [snip]
>> >>>
>> >>>     Out of curiousity, have you looked at kvmtool
>> >>>     (
>> https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.kernel.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Fwill%2Fkvmtool.git%2F&data=02%7C01%7Cjessfraz%40microsoft.com%7C604dbe2ada034e62d2f908d5cbf07f6b%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636639156156262890&sdata=xEWVp9B0rIFl5Ez1cGTMz9ClFs5Ril%2FTJN2SgVta824%3D&reserved=0
>> )?
>> >>>
>> >>>     Forking qemu rather than building on top of it (or using something
>> else)
>> >>>     isn't going to end well IMO.
>> >>>     _______________________________________________
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>> >>>
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