CVE-2026-89961 powerpc/mm: fix wrong addr_pfn tracking in compound vmemmap population

In the Linux kernel, the following vulnerability has been resolved: powerpc/mm: fix wrong addrpfn tracking in compound vmemmap population vmemmappopulatecompoundpages uses addrpfn to determine the PFN offset within a compound page and to decide whether the current vmemmap slot should be populated...