CVE-2024-42126 is a vulnerability in the Linux kernel affecting powerpc architectures. It involves the use of nmi_enter() and nmi_exit() functions during real mode interrupt handling, which can lead to kernel crashes when per-CPU variables are allocated from the vmalloc area. This issue arises particularly when the kernel is configured with CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK and the kernel command line forces percpu allocation from the vmalloc area. The vulnerability has been fixed by avoiding nmi_enter()/nmi_exit() calls in real mode if the percpu first chunk is not embedded.