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

[Paolo Bonzini <pbonzini@redhat.com>]

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@kernel.org> wrote:
>>> From: Arnd Bergmann <arnd@arndb.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