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

[Thomas Huth <thuth@xxxxxxxxxx>]

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@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.
> 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