mm/memory: document restore_exclusive_pte()

}

#endif

/**

 * restore_exclusive_pte - Restore a device-exclusive entry

 * @vma: VMA covering @address

 * @folio: the mapped folio

 * @page: the mapped folio page

 * @address: the virtual address

 * @ptep: pte pointer into the locked page table mapping the folio page

 * @orig_pte: pte value at @ptep

 *

 * Restore a device-exclusive non-swap entry to an ordinary present pte.

 *

 * The folio and the page table must be locked, and MMU notifiers must have

 * been called to invalidate any (exclusive) device mappings.

 *

 * Locking the folio makes sure that anybody who just converted the pte to

 * a device-exclusive entry can map it into the device to make forward

 * progress without others converting it back until the folio was unlocked.

 *

 * If the folio lock ever becomes an issue, we can stop relying on the folio

 * lock; it might make some scenarios with heavy thrashing less likely to

 * make forward progress, but these scenarios might not be valid use cases.

 *

 * Note that the folio lock does not protect against all cases of concurrent

 * page table modifications (e.g., MADV_DONTNEED, mprotect), so device drivers

 * must use MMU notifiers to sync against any concurrent changes.

 */

static void restore_exclusive_pte(struct vm_area_struct *vma,

		struct folio *folio, struct page *page, unsigned long address,

		pte_t *ptep, pte_t orig_pte)