CVE-2024-50222

In the Linux kernel, the following vulnerability has been resolved:

iov_iter: fix copy_page_from_iter_atomic() if KMAP_LOCAL_FORCE_MAP

generic/077 on x86_32 CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP=y with highmem,
on huge=always tmpfs, issues a warning and then hangs (interruptibly):

WARNING: CPU: 5 PID: 3517 at mm/highmem.c:622 kunmap_local_indexed+0x62/0xc9
CPU: 5 UID: 0 PID: 3517 Comm: cp Not tainted 6.12.0-rc4 #2
...
copy_page_from_iter_atomic+0xa6/0x5ec
generic_perform_write+0xf6/0x1b4
shmem_file_write_iter+0x54/0x67

Fix copy_page_from_iter_atomic() by limiting it in that case
(include/linux/skbuff.h skb_frag_must_loop() does similar).

But going forward, perhaps CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP is too
surprising, has outlived its usefulness, and should just be removed?