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Thorsten Leemhuis (acct. 1/4)

The "x86: 32-bit cleanups" patch series[1] from @arnd hit -next and thus is slated for inclusion in 6.15.

It removes some code like CONFIG_HIGHMEM64G that complicates things in some areas, but is mainly "about running 32-bit kernels on 64-bit hardware, which usually works but should probably be discouraged more clearly by only providing support for features that are used on real 32-bit hardware" – and unlikely to be used in the wild.

[1] lore.kernel.org/all/2025022621

Feb 28, 2025, 10:16 AM·Public
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Thorsten Leemhuis (acct. 1/4)

2/ Ohh, and FWIW, see also this message from @arnd about the rough plan to remove the sometimes painful code behind CONFIG_ HIGHMEM completely, which would make @torvalds "very very happy":

lore.kernel.org/all/0047f565-a

But as can be seen from that mail, it's quite a bit of work that needs to be done. But removing CONFIG_HIGHMEM64G and the other changes were hopefully a good step in that direction.

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Mathieu

@kernellogger @arnd Oh and it includes a plan to get rid of HIGHMEM, that's lovely.

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Thorsten Leemhuis (acct. 1/4)

@mathieu good point, added a separate toot to highlight it 👍

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Pavel Machek
@kernellogger @arnd @torvalds Highmem is needed to keep 32-bit machines useful. Without it, limit is 1GB RAM or something like that.You need 2GB RAM for useful web browser... Plus, Thinkpad X60, the second best notebook ever, is 32bit. I have one with 3GB, and it would be nice to keep it going.
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waldi

@pavel The X61 is almost the same device and comes with the first 64 bit CPU, but distributions are starting do drop support for those as well. But at some time after almost 20 years it should be okay to retire hardware.

32 bit is also not longer suitable for web browsing if you ever execute untrusted code there. It just lacks all the security hardening that came and are important.

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Pavel Machek
@waldi Yeah, that's why it is second-best notebook. Still, don't break it :-).
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Pavel Machek
@waldi (And we can talk about security next time spectre-like vulnerability appears in recent CPUs. Hardening is cool, but we know the modern CPUs are broken by design, and what we do in kernel are workarounds, not fixes. Unfortunately, X60 is new enough to have speculation bugs, but I'm pretty sure exploits will not work there :-) ).
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Arnd Bergmann

@pavel are you going to be at EmbeddedWorld? I have an old X61t that I'm no longer using, and I think you can swap out the motherboard to upgrade your X60 to a Core 2 Duo with 8GB.

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Martin Roukala (né Peres)

@arnd @pavel Ha ha, yeah! At this point, there is enough free hardware thrown in the garbage for everyone still using 32 bits x86 to upgrade to a faster and more power efficient hardware.

No sense in maintaining such old hardware in these conditions.

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Pavel Machek
@arnd Embedded world -- likely not. Probably ELCE later this year.

For the full disclosure, I have X220 and X230 I'm not using, so I'd basically add X61t to the collection. Would like to have tablet thinkpad :-).

Anyway, I see that x86-32 is ugly. OTOH it is well-known architecture and now patent-free... and FPGA toys such as MISTer https://www.retrorgb.com/mister.html are powerful enough to do 486sx. That can't run today's Linux, but feels close. One day, I'd like run Linux on free hardware, and x86-32 may be reasonable way to do that.
RetroRGBMiSTer FPGA HardwareThe MiSTer is an open-source project that emulates consoles, computers and arcade boards via FPGA - This is different from software emulation, as there's potential for performance exactly like the original.  While software emulation has the potential to be really accurate as well, you're much more l
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Arnd Bergmann

@pavel I can certainly bring it to ELCE in August, but you may have to remind me. The outside plastic on the X61 has turned into a sticky mess, so I wouldn't recommend it for anything other than a parts donor. I also haven't tried turning it on in probably a decade, but I'm fairly sure it was working back then (and already sticky). Restoring it should be possible but not fun.

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