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

From: Arnd Bergmann <arnd@arndb.de>
To: Olof Johansson <olof@lixom.net>
Cc: Anders Berg <anders.berg@lsi.com>,
	Russell King <linux@arm.linux.org.uk>,
	kvm list <kvm@vger.kernel.org>, Marc Zyngier <maz@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Will Deacon <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu,
	Linux ARM Mailing List <linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC PATCH 0/5] Removing support for 32bit KVM/arm host
Date: Mon, 10 Feb 2020 16:54:52 +0100	[thread overview]
Message-ID: <CAK8P3a1pi3yBVMdXQyZsm_NFLn=UrVRgQ2O5b3-RmF9JTi5z7A@mail.gmail.com> (raw)
In-Reply-To: <CAOesGMhHkez-5vxwWuzXc2Rm=dYYWjMX9C8AewVy9GDWuZcwMw@mail.gmail.com>

On Mon, Feb 10, 2020 at 4:32 PM Olof Johansson <olof@lixom.net> wrote:
> On Mon, Feb 10, 2020 at 3:13 PM Marc Zyngier <maz@kernel.org> 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
> >
> > So here it is: unless someone screams and shows that they rely on
> > KVM/arm to be maintained upsteam, I'll remove 32bit host support
> > form the tree. One of the reasons that makes me confident nobody is
> > using it is that I never receive *any* bug report. Yes, it is perfect.
> > But if you depend on KVM/arm being available in mainline, please shout.
> >
> > To reiterate: 32bit guest support for arm64 stays, of course. Only
> > 32bit host goes. Once this is merged, I plan to move virt/kvm/arm to
> > arm64, and cleanup all the now unnecessary abstractions.

I think this makes a lot of sense: we are seeing fewer new 32-bit
systems that have enough RAM to be a usable virtualization host,
as most new boards with more than 1GB of RAM typically pick 64-bit
SoCs, and on less than 1GB it gets awfully tight to do anything useful.

> Since I'm generally happy to drop legacy code that has no users, with
> the "if there are any significant users that speak up, I'll revoke my
> support" caveat:
>
> Acked-by: Olof Johansson <olof@lixom.net>

Same here

Acked-by: Arnd Bergmann <arnd@arndb.de>
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