[PATCH 1/2] docs/about: Deprecate 32-bit x86 hosts and qemu-system-i386

[Thomas Huth]

On 27/02/2023 21.25, Richard Henderson wrote:
> On 2/27/23 01:50, Daniel P. Berrangé wrote:
>> On Mon, Feb 27, 2023 at 12:10:49PM +0100, Thomas Huth wrote:
>>> Hardly anybody still uses 32-bit x86 hosts today, so we should
>>> start deprecating them to finally have less test efforts.
>>> With regards to 32-bit KVM support in the x86 Linux kernel,
>>> the developers confirmed that they do not need a recent
>>> qemu-system-i386 binary here:
>>>
>>>   https://lore.kernel.org/kvm/Y%2ffkTs5ajFy0hP1U@google.com/
>>>
>>> Signed-off-by: Thomas Huth <thuth at redhat.com>
>>> ---
>>>   docs/about/deprecated.rst | 13 +++++++++++++
>>>   1 file changed, 13 insertions(+)
>>>
>>> diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
>>> index 15084f7bea..98517f5187 100644
>>> --- a/docs/about/deprecated.rst
>>> +++ b/docs/about/deprecated.rst
>>> @@ -196,6 +196,19 @@ CI coverage support may bitrot away before the 
>>> deprecation process
>>>   completes. The little endian variants of MIPS (both 32 and 64 bit) are
>>>   still a supported host architecture.
>>> +32-bit x86 hosts and ``qemu-system-i386`` (since 8.0)
>>> +'''''''''''''''''''''''''''''''''''''''''''''''''''''
>>> +
>>> +Testing 32-bit x86 host OS support takes a lot of precious time during the
>>> +QEMU contiguous integration tests, and considering that most OS vendors
>>> +stopped shipping 32-bit variants of their x86 OS distributions and most
>>> +x86 hardware from the past >10 years is capable of 64-bit, keeping the
>>> +32-bit support alive is an inadequate burden for the QEMU project. Thus
>>> +QEMU will soon drop the support for 32-bit x86 host systems and the
>>> +``qemu-system-i386`` binary. Use ``qemu-system-x86_64`` (which is a proper
>>> +superset of ``qemu-system-i386``) on a 64-bit host machine instead.
>>
>> I feel like we should have separate deprecation entries for the
>> i686 host support, and for qemu-system-i386 emulator binary, as
>> although they're related they are independant features with
>> differing impact.
> 
> Agreed.

OK, fair, I'll rework my patch according to your suggestion, Daniel.

>> 32-bit x86 hosts
>> ''''''''''''''''
>>
>> Support for 32-bit x86 host deployments is increasingly uncommon in
>> mainstream Linux distributions given the widespread availability of
>> 64-bit x86 hardware. The QEMU project no longer considers 32-bit
>> x86 support to be an effective use of its limited resources, and
>> thus intends to discontinue it.
>>
>> Current users of QEMU on 32-bit x86 hosts should either continue
>> using existing releases of QEMU, with the caveat that they will
>> no longer get security fixes, or migrate to a 64-bit platform
>> which remains capable of running 32-bit guests if needed.
> Ack.
> 
>>
>> ``qemu-system-i386`` binary removal
>> '''''''''''''''''''''''''''''''''''
>>
>> The ``qemu-system-x86_64`` binary can be used to run 32-bit guests
>> by selecting a 32-bit CPU model, including KVM support on x86_64
>> hosts. Once support for the 32-bit x86 host platform is discontinued,
>> the ``qemu-system-i386`` binary will be redundant.
> 
> Missing "kvm" in this last sentence?  It is otherwise untrue for tcg.

I assume that Daniel only thought of 32-bit x86 hosts here, but indeed, it's 
untrue for non-x86 32-bit hosts. So this really should refer to KVM on 
32-bit x86 hosts instead. I'll rephrase it in v2.

  Thomas