Re: [RFC PATCH 0/5] Removing support for 32bit KVM/arm host

[Marc Zyngier <maz@xxxxxxxxxx>]

On 2020-02-20 13:32, Robin Murphy wrote:
> On 20/02/2020 1:15 pm, Marc Zyngier wrote:
> > Hi Marek,
> >
> > On 2020-02-20 12:44, Marek Szyprowski wrote:
> > > Hi Marc,
> > >
> > > On 10.02.2020 15:13, Marc Zyngier wrote:
> > > > KVM/arm was merged just over 7 years ago, and has lived a very quiet
> > > > life so far. It mostly works if you're prepared to deal with its
> > > > limitations, it has been a good prototype for the arm64 version,
> > > > but it suffers a few problems:
> > > >
> > > > - It is incomplete (no debug support, no PMU)
> > > > - It hasn't followed any of the architectural evolutions
> > > > - It has zero users (I don't count myself here)
> > > > - It is more and more getting in the way of new arm64 developments
> > >
> > > That is a bit sad information. Mainline Exynos finally got everything
> > > that was needed to run it on the quite popular Samsung 
> > > Exynos5422-based
> > > Odroid XU4/HC1/MC1 boards. According to the Odroid related forums it 
> > > is
> > > being used. We also use it internally at Samsung.
> >
> > Something like "too little, too late" springs to mind, but let's be
> > constructive. Is anyone using it in a production environment, where
> > they rely on the latest mainline kernel having KVM support?
> >
> > The current proposal is to still have KVM support in 5.6, as well as
> > ongoing support for stable kernels. If that's not enough, can you 
> > please
> > explain your precise use case?
>
> Presumably there's no *technical* reason why the stable subset of v7
> support couldn't be stripped down and brought back private to arch/arm
> if somebody really wants and is willing to step up and look after it?

There is no technical reason at all, just a maintenance effort.

The main killer is the whole MMU code, which I'm butchering with NV,
and that I suspect Will will also turn upside down with his stuff.
Not to mention the hypercall interface that will need a complete 
overhaul.

If we wanted to decouple the two, we'd need to make the MMU code, the
hypercalls, arm.c and a number of other bits private to 32bit.

        M.
--
Jazz is not dead. It just smells funny...
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