[RFC PATCH] docs/about/deprecated: Deprecate 32-bit host systems

[Thomas Huth]

On 04/04/2023 17.42, BALATON Zoltan wrote:
> On Tue, 4 Apr 2023, Cédric Le Goater wrote:
>> [ adding Zoltan ]
>>
>> On 4/4/23 16:00, Thomas Huth wrote:
>>> On 05/02/2023 23.12, Mark Cave-Ayland wrote:
>>>> On 30/01/2023 20:45, Alex Bennée wrote:
>>>>
>>>>> Daniel P. Berrangé <berrange at redhat.com> writes:
>>>>>
>>>>>> On Mon, Jan 30, 2023 at 11:47:02AM +0000, Peter Maydell wrote:
>>>>>>> On Mon, 30 Jan 2023 at 11:44, Thomas Huth <thuth at redhat.com> wrote:
>>>>>>>>
>>>>>>>> Testing 32-bit host OS support takes a lot of precious time during 
>>>>>>>> the QEMU
>>>>>>>> contiguous integration tests, and considering that many OS vendors 
>>>>>>>> stopped
>>>>>>>> shipping 32-bit variants of their OS distributions and most hardware 
>>>>>>>> from
>>>>>>>> the past >10 years is capable of 64-bit
>>>>>>>
>>>>>>> True for x86, not necessarily true for other architectures.
>>>>>>> Are you proposing to deprecate x86 32-bit, or all 32-bit?
>>>>>>> I'm not entirely sure about whether we're yet at a point where
>>>>>>> I'd want to deprecate-and-drop 32-bit arm host support.
>>>>>>
>>>>>> Do we have a feeling on which aspects of 32-bit cause us the support
>>>>>> burden ? The boring stuff like compiler errors from mismatched integer
>>>>>> sizes is mostly quick & easy to detect simply through a cross compile.
>>>>>>
>>>>>> I vaguely recall someone mentioned problems with atomic ops in the past,
>>>>>> or was it 128-bit ints, caused implications for the codebase ?
>>>>>
>>>>> Atomic operations on > TARGET_BIT_SIZE and cputlb when
>>>>> TCG_OVERSIZED_GUEST is set. Also the core TCG code and a bunch of the
>>>>> backends have TARGET_LONG_BITS > TCG_TARGET_REG_BITS ifdefs peppered
>>>>> throughout.
>>>>
>>>> I am one of an admittedly small group of people still interested in 
>>>> using KVM-PR on ppc32 to boot MacOS, although there is some interest on 
>>>> using 64-bit KVM-PR to run super-fast MacOS on modern Talos hardware.
>>>>
>>>>  From my perspective losing the ability to run 64-bit guests on 32-bit 
>>>> hardware with TCG wouldn't be an issue, as long as it were still 
>>>> possible to use qemu-system-ppc on 32-bit hardware using both TCG and 
>>>> KVM to help debug the remaining issues.
>>>
>>>   Hi Mark!
>>>
>>> Just out of curiosity (since we briefly talked about 32-bit KVM on ppc in 
>>> today's QEMU/KVM call - in the context of whether qemu-system-ppc64 is a 
>>> proper superset of qemu-system-ppc when it comes to building a unified 
>>> qemu-system binary): What host machine are you using for running KVM-PR? 
>>> And which QEMU machine are you using for running macOS? The mac99 or the 
>>> g3beige machine?
>>
>> Zoltan, what about the pegasos2 and sam460ex machines ? can they be run 
>> under KVM ?
> 
> I don't know as I don't have PPC hardware to test on but theoretically they 
> should work. Although BookE KVM was dropped from Linux I think so sam460ex 
> could only work with an old kernel on a BookE host which is now rare 
[...]

Thanks for your explanations, that indeed helps to understand the situation!

But are you sure about the BookE KVM removal in the Linux kernel? ... when I 
look at the arch/powerpc/kvm/ folder there, I can still see some files there 
with "booke" in the name?

  Thomas