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Thu, 20 Feb 2020 10:29:11 +0000 MIME-Version: 1.0 Date: Thu, 20 Feb 2020 10:29:11 +0000 From: Marc Zyngier To: Jan Kiszka Subject: Re: [RFC PATCH 0/5] Removing support for 32bit KVM/arm host In-Reply-To: References: <20200210141324.21090-1-maz@kernel.org> Message-ID: <535d8a4498d81b4901dfab232638d865@kernel.org> X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/1.3.10 X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: jan.kiszka@siemens.com, arnd@arndb.de, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, pbonzini@redhat.com, Christoffer.Dall@arm.com, will@kernel.org, qperret@google.com, linux@arm.linux.org.uk, vladimir.murzin@arm.com, anders.berg@lsi.com, jailhouse-dev@googlegroups.com, jean-philippe.brucker@arm.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Cc: jailhouse-dev@googlegroups.com, Anders Berg , Russell King , Arnd Bergmann , kvm list , jean-philippe.brucker@arm.com, Linux ARM , Paolo Bonzini , Will Deacon , kvmarm@lists.cs.columbia.edu X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu 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 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... _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm