linux-kernel - Re: [RFC 0/5] KVM: drop 32-bit host support on all architectures

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <79b9abfe-cfb8-4ef0-8a4b-7b87787e6549@redhat.com>
Date: Fri, 13 Dec 2024 09:20:05 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Arnd Bergmann <arnd@...db.de>, "A. Wilcox" <AWilcox@...cox-tech.com>,
 Arnd Bergmann <arnd@...nel.org>
Cc: kvm@...r.kernel.org, Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
 Huacai Chen <chenhuacai@...nel.org>, Jiaxun Yang <jiaxun.yang@...goat.com>,
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Naveen N Rao <naveen@...nel.org>, Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Alexander Graf <graf@...zon.com>, Crystal Wood <crwood@...hat.com>,
 Anup Patel <anup@...infault.org>, Atish Patra <atishp@...shpatra.org>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
 <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Sean Christopherson <seanjc@...gle.com>, Thomas Gleixner
 <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
 Vitaly Kuznetsov <vkuznets@...hat.com>, David Woodhouse
 <dwmw2@...radead.org>, Paul Durrant <paul@....org>,
 Marc Zyngier <maz@...nel.org>, linux-kernel@...r.kernel.org,
 linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org
Subject: Re: [RFC 0/5] KVM: drop 32-bit host support on all architectures

On 12/13/24 09:03, Arnd Bergmann wrote:
> On Fri, Dec 13, 2024, at 04:51, A. Wilcox wrote:
>> On Dec 12, 2024, at 6:55 AM, Arnd Bergmann <arnd@...nel.org> wrote:
>>> From: Arnd Bergmann <arnd@...db.de>
>>>
>>> I submitted a patch to remove KVM support for x86-32 hosts earlier
>>> this month, but there were still concerns that this might be useful for
>>> testing 32-bit host in general, as that remains supported on three other
>>> architectures. I have gone through those three now and prepared similar
>>> patches, as all of them seem to be equally obsolete.
>>>
>>> Support for 32-bit KVM host on Arm hardware was dropped back in 2020
>>> because of lack of users, despite Cortex-A7/A15/A17 based SoCs being
>>> much more widely deployed than the other virtualization capable 32-bit
>>> CPUs (Intel Core Duo/Silverthorne, PowerPC e300/e500/e600, MIPS P5600)
>>> combined.
>>
>>
>> I do use 32-bit KVM on a Core Duo “Yonah” and a Power Mac G4 (MDD), for
>> purposes of bisecting kernel issues without having to reboot the host
>> machine (when it can be duplicated in a KVM environment).
>>
>> I suppose it would still be possible to run the hosts on 6.12 LTS for
>> some time with newer guests, but it would be unfortunate.
> 
> Would it be an option for you to just test those kernels on 64-bit
> machines? I assume you prefer to do native builds on 32-bit hardware
> because that fits your workflow, but once you get into debugging
> in a virtual machine, the results should generally be the same when
> building and running on a 64-bit host for both x86-32 and ppc32-classic,
> right?

Certainly for x86-32; ppc32 should be able to use PR-state (aka trap and 
emulate) KVM on a 64-bit host but it's a bit more picky.  Another 
possibility for ppc32 is just emulation with QEMU.

Paolo