Juergen Gross [off-list ref] writes:
The long term plan has been to replace Xen PV guests by PVH. The first
victim of that plan are now 32-bit PV guests, as those are used only
rather seldom these days. Xen on x86 requires 64-bit support and with
Grub2 now supporting PVH officially since version 2.04 there is no
need to keep 32-bit PV guest support alive in the Linux kernel.
Additionally Meltdown mitigation is not available in the kernel running
as 32-bit PV guest, so dropping this mode makes sense from security
point of view, too.
Normally we have a deprecation period for feature removals like this.
You would make the kernel print a warning for some releases, and when
no user complains you can then remove. If a user complains you can't.
-Andi