Re: [PATCH v6 2/9] x86/resctrl: Require 64-bit x86 for resctrl support

[Dave Hansen]

On 8/25/26 06:12, Chen Yu wrote:
> "32-bit x86 is maintained for legacy reasons. New CPU features are generally
> not enabled for 32-bit system, its test coverage keeps shrinking, and modern
> 32-bit distributions have become rare."

What would folks think about plopping something like the following text
in to Documentation/arch/x86/32bit-kernels.rst ?

Would that clear things up?

---

=========================================
Supporting new features on 32-bit kernels
=========================================

While it is possible to compile and run a 32-bit kernel on 64-bit
capable hardware, it is impractical and discouraged. Processors
capable of running 64-bit kernels are expected to do so.

The last 32-bit processor to come out of Intel or AMD was a Quark CPU
in 2013. Before that the most recent were some Atom CPUs in 2008.

Distros supporting 32-bit kernels and userspace are disappearing.  For
example, in 2026 Ubuntu and Fedora no longer have support, with Debian
being the most notable holdout still maintaining 32-bit options.

New Processor Features
======================

When adding support for a new processor feature in 2026 and beyond it
should, by default, be:

        config NEW_SNAZZY_CPU_FEATURE
                depends X86_64

This ensures that the folks developing this feature do not waste
resources making it work on 32-bit kernels running on 64-bit hardware.

It is also acceptable to add this restriction to existing processor
features if 32-bit kernel support is adding maintenance burden,
especially if the feature was only ever available on 64-bit processors.

New Software Features
=====================

Let's say you are enhancing ftrace or adding a debugging feature that
has no strict dependency on processor features. It does not need to
be restricted to 64-bit only. But you might want to consider doing so
if it simplifies your implementation.

For instance, sometimes it adds complexity to support HIGHMEM. You may
add a dependency on X86_64 in cases where it is impractical or simply
challenging to support 32-bit kernels.