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From: Marc Zyngier <maz@kernel.org>
To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: jailhouse-dev@googlegroups.com, Anders Berg <anders.berg@lsi.com>,
	Russell King <linux@arm.linux.org.uk>,
	Arnd Bergmann <arnd@arndb.de>, kvm list <kvm@vger.kernel.org>,
	jean-philippe.brucker@arm.com,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Will Deacon <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu
Subject: Re: [RFC PATCH 0/5] Removing support for 32bit KVM/arm host
Date: Thu, 20 Feb 2020 10:29:11 +0000
Message-ID: <535d8a4498d81b4901dfab232638d865@kernel.org> (raw)
In-Reply-To: <ea7bc1d0-0a11-8ed6-da70-d603d8107bf6@siemens.com>

On 2020-02-19 15:46, Jan Kiszka wrote:
> On 19.02.20 16:09, Arnd Bergmann 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.
>>> 
>>> The patches have been generated with the -D option to avoid spamming
>>> everyone with huge diffs, and there is a kvm-arm/goodbye branch in
>>> my kernel.org repository.
>> 
>> Just one more thought before it's gone: is there any shared code
>> (header files?) that is used by the jailhouse hypervisor?
>> 
>> If there is, are there any plans to merge that into the mainline 
>> kernel
>> for arm32 in the near future?
>> 
>> I'm guessing the answer to at least one of those questions is 'no', so
>> we don't need to worry about it, but it seems better to ask.
> 
> Good that you mention it: There is one thing we share on ARM (and
> ARM64), and that is the hypervisor enabling stub, to install our own
> vectors. If that was to be removed as well, we would have to patch it
> back downstream. So far, we only carry few EXPORT_SYMBOL patches for
> essential enabling.

I actually have a few extra patches on top of the series, one of them
actually removing the ability to register new vectors (mostly because
I don't like leaving unused stuff behind), see [1]. I'll post an update
so that we can discuss whether we want this particular to stay or not.

> That said, I was also starting to think about how long we will
> continue to support Jailhouse on 32-bit ARM. We currently have no
> supported SoC there that comes with an SMMU, and I doubt to see one
> still showing up. So, Jailhouse on ARM is really just a testing/demo
> case, maybe useful (but I didn't get concrete feedback) for cleaner
> collaborative AMP for real-time purposes, without security concerns. I
> assume 32-bit ARM will never be part of what would be proposed of
> Jailhouse for upstream.

I guess we all come to the same conclusion...

         M.

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/commit/?h=kvm-arm/goodbye&id=0943dd119105b65197adffda52c402cce28da56d
-- 
Jazz is not dead. It just smells funny...
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Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20200210141344eucas1p25a6da0b0251931ef3659397a6f34c0c3@eucas1p2.samsung.com>
2020-02-10 14:13 ` Marc Zyngier
2020-02-10 14:13   ` [RFC PATCH 1/5] arm: Unplug KVM from the build system Marc Zyngier
2020-02-10 14:13   ` [RFC PATCH 2/5] arm: Remove KVM from config files Marc Zyngier
2020-02-10 14:13   ` [RFC PATCH 3/5] arm: Remove 32bit KVM host support Marc Zyngier
2020-02-10 14:13   ` [RFC PATCH 4/5] arm: Remove HYP/Stage-2 page-table support Marc Zyngier
2020-02-10 14:13   ` [RFC PATCH 5/5] arm: Remove GICv3 vgic compatibility macros Marc Zyngier
2020-02-10 15:21   ` [RFC PATCH 0/5] Removing support for 32bit KVM/arm host Olof Johansson
2020-02-10 15:54     ` Arnd Bergmann
2020-02-10 15:46   ` Will Deacon
2020-02-10 16:25   ` Russell King - ARM Linux admin
2020-02-10 16:26     ` Russell King - ARM Linux admin
2020-02-11 15:12   ` Vladimir Murzin
2020-02-11 15:23   ` Catalin Marinas
2020-02-17  0:14   ` Linus Walleij
2020-02-19 13:53   ` Stefan Agner
2020-02-20 11:01     ` Marc Zyngier
2020-02-19 14:56   ` Christoffer Dall
2020-02-19 15:09   ` Arnd Bergmann
2020-02-19 15:46     ` Jan Kiszka
2020-02-20 10:29       ` Marc Zyngier [this message]
2020-02-20 12:44   ` Marek Szyprowski
2020-02-20 13:15     ` Marc Zyngier
2020-02-20 13:17       ` Paolo Bonzini
2020-02-20 13:32       ` Robin Murphy
2020-02-20 14:01         ` Marc Zyngier
2020-02-20 14:38           ` Robin Murphy
2020-02-22 14:21   ` Takashi Yoshi
2020-02-22 14:40   ` Takashi Yoshi
2020-02-22 21:31     ` Arnd Bergmann
2020-02-25 21:34       ` Takashi Yoshi

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