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

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: mm/damon/vaddr: do not repeat pte_offset_map_lock() until success DAMON's virtual address space operation set implementation (vaddr) calls pte_offset_map_lock() inside the page table walk callback function. This is for reading and writing page table accessed bits. If pte_offset_map_lock() fails, it retries by returning the page table walk callback function with ACTION_AGAIN. pte_offset_map_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.

References

• https://git.kernel.org/stable/c/677ebfe5d00f94adec0c0204f6e6e2a82d3f77bf
• https://git.kernel.org/stable/c/ac42320ec873bfe726141069cfdd90ee5bc4e885
• https://git.kernel.org/stable/c/0ccd91cf749536d41307a07e60ec14ab0dbf21f5
• https://git.kernel.org/stable/c/b93af2cc8e036754c0d9970d9ddc47f43cc94b9f