Re: [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@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@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