In the Linux kernel, the following vulnerability has been resolved: mm/util: don't read __page_2...

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

mm/util: don't read __page_2 for order-1 folios in snapshot_page()

snapshot_page() currently reads __page_2 after checking nr_pages > 1, but it should only do so when nr_pages > 2.

If an order-1 folio is allocated at the end of a vmemmap section, __page_2 will not exist and reading it will cause a fault.

During DLPAR memory remove on a 22 TB ppc64le LPAR, snapshot_page() oopsed on the page isolation path while reading an order-1 folio's __page_2 from an adjacent absent section (unmapped vmemmap).

Fix this to avoid reading memmap that doesn't exist (e.g., a vmemmap hole).