CVE-2025-40218

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

mm/damon/vaddr: do not repeat pteoffsetmap_lock() until success

DAMON's virtual address space operation set implementation (vaddr) calls pteoffsetmaplock() inside the page table walk callback function. This is for reading and writing page table accessed bits. If pteoffsetmaplock() fails, it retries by returning the page table walk callback function with ACTION_AGAIN.

pteoffsetmap_lock() can continuously fail if the target is a pmd migration entry, though. Hence it could cause an infinite page table walk if the migration cannot be done until the page table walk is finished. This indeed caused a soft lockup when CPU hotplugging and DAMON were running in parallel.

Avoid the infinite loop by simply not retrying the page table walk. DAMON is promising only a best-effort accuracy, so missing access to such pages is no problem.