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

[Daniel P. Berrangé <berrange@xxxxxxxxxx>]

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@xxxxxxxxxx/
> 
> Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx>
> ---
>  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. eg removing qemu-system-i386 affects all
host architectures, not merely 32-bit x86 host, so I think we
can explain the impact more clearly if we separate them.

How about something like....


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.

``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. Current users are
recommended to reconfigure their systems to use the ``qemu-system-x86_64``
binary.



Same point for the next patch about 32-bit arm vs qemu-system-arm
binary.

With regards,
Daniel
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