In the Linux kernel, the following vulnerability has been resolved: mm: migrate_device: fix pte_pfn/pte_dirty called on non-present PTE pt

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

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

pte_pfn() and pte_dirty() have undefined behaviour when called on a
non-present PTE. In migrate_vma_collect_pmd(), these functions may be
invoked on non-present entries (e.g., device-private entries), leading
to potential crashes from pte_pfn() or incorrect dirty folio accounting
from pte_dirty(). Fix both by guarding with pte_present() checks.