CVE-2026-80686 mm: migrate_device: fix pte_pfn/pte_dirty called on non-present PTE

In the Linux kernel, the following vulnerability has been resolved: mm: migratedevice: fix ptepfn/ptedirty called on non-present PTE ptepfn and ptedirty have undefined behaviour when called on a non-present PTE. In migratevmacollectpmd, these functions may be invoked on non-present entries e.g.,...