Re: [PATCH v2 00/14] meson: Deprecate 32-bit host support

[Jan Beulich <jbeulich@xxxxxxxx>]

On 04.02.2025 09:19, Juergen Gross wrote:
> On 03.02.25 23:43, Stefano Stabellini wrote:
>> +Xen maintainers
>>
>>
>> On Mon, 3 Feb 2025, Richard Henderson wrote:
>>> On 2/3/25 04:54, Paolo Bonzini wrote:
>>>> On 2/3/25 04:18, Richard Henderson wrote:
>>>>> v1: 20250128004254.33442-1-richard.henderson@xxxxxxxxxx
>>>>>
>>>>> For v2, immediately disable 64-on-32 TCG.
>>>>>
>>>>> I *suspect* that we should disable 64-on-32 for *all* accelerators.
>>>>> The idea that an i686 binary on an x86_64 host may be used to spawn
>>>>> an x86_64 guest via kvm is silly and a bit more than niche.
>>>>
>>>> At least Xen used to be commonly used with 32-bit dom0, because it saved
>>>> memory and dom0 would map in guest buffers as needed.  I'm not sure how
>>>> common that is these days, perhaps Stefano knows.
>>>
>>> As a data-point, debian does not ship libxen-dev for i686.
>>> We cannot build-test this configuration at all.
>>>
>>> I can build-test Xen for armhf, and I guess it would use i386-softmmu; it's
>>> unclear whether x86_64-softmmu and aarch64-softmmu are relevant or useful 
>>> for
>>> an armhf host, or as an armhf binary running on an aarch64 host.
>>
>>
>> On the Xen side, there are two different use cases: x86 32-bit and ARM
>> 32-bit.
>>
>> For x86 32-bit, while it was a very important use case in the past, I
>> believe it is far less so now. I will let the x86 maintainers comment on
>> how important it is today.
> 
> As dom0 on x86 is a PV guest per default and Linux doesn't support running as 
> a
> 32-bit PV guest since a few years now, I guess there is no need to support 
> qemu
> as 32-bit on x86 for Xen.

Yet then, just to mention it, you can run a 64-bit PV Dom0 kernel underneath
an otherwise 32-bit distro. I've been doing this successfully for very many
years (with a very small kernel adjustment, just to work around an apparent
shortcoming in system init scripts).

Jan