[REGRESSION] x86_32 boot hang in 6.19-rc7 caused by b505f1944535 ("x86/kfence: avoid writing L1TF-vulnerable PTEs")

[Ryusuke Konishi]

Hi All,

I am reporting a boot regression in v6.19-rc7 on an x86_32
environment. The kernel hangs immediately after "Booting the kernel"
and does not produce any early console output.

A git bisect identified the following commit as the first bad commit:
b505f1944535 ("x86/kfence: avoid writing L1TF-vulnerable PTEs")

Environment and Config:
- Guest Arch: x86_32  (one of my test VMs)
- Memory Config: # CONFIG_X86_PAE is not set
- KFENCE Config: CONFIG_KFENCE=y
- Host/Hypervisor: x86_64 host running KVM

The system fails to boot at a very early stage. I have confirmed that
reverting commit b505f1944535 on top of v6.19-rc7 completely resolves
the issue, and the kernel boots normally.

Could you please verify if this change is compatible with x86_32
(non-PAE) configurations?
I am happy to provide my full .config or test any potential fixes.

Best regards,
Ryusuke Konishi