Function pmap_clear_modify

freebsd/arm64/arm64/pmap.c:5787–5869

* Clear the modify bits on the specified physical page. */

 *	Clear the modify bits on the specified physical page.
 */
void
pmap_clear_modify(vm_page_t m)
{
	struct md_page *pvh;
	struct rwlock *lock;
	pmap_t pmap;
	pv_entry_t next_pv, pv;
	pd_entry_t *l2, oldl2;
	pt_entry_t *l3, oldl3;
	vm_offset_t va;
	int md_gen, pvh_gen;

	KASSERT((m->oflags & VPO_UNMANAGED) == 0,
	    ("pmap_clear_modify: page %p is not managed", m));
	vm_page_assert_busied(m);

	if (!pmap_page_is_write_mapped(m))
		return;
	pvh = (m->flags & PG_FICTITIOUS) != 0 ? &pv_dummy : page_to_pvh(m);
	lock = VM_PAGE_TO_PV_LIST_LOCK(m);
	rw_wlock(lock);
restart:
	TAILQ_FOREACH_SAFE(pv, &pvh->pv_list, pv_next, next_pv) {
		pmap = PV_PMAP(pv);
		PMAP_ASSERT_STAGE1(pmap);
		if (!PMAP_TRYLOCK(pmap)) {
			pvh_gen = pvh->pv_gen;
			rw_wunlock(lock);
			PMAP_LOCK(pmap);
			rw_wlock(lock);
			if (pvh_gen != pvh->pv_gen) {
				PMAP_UNLOCK(pmap);
				goto restart;
			}
		}
		va = pv->pv_va;
		l2 = pmap_l2(pmap, va);
		oldl2 = pmap_load(l2);
		/* If oldl2 has ATTR_SW_DBM set, then it is also dirty. */
		if ((oldl2 & ATTR_SW_DBM) != 0 &&
		    pmap_demote_l2_locked(pmap, l2, va, &lock) &&
		    (oldl2 & ATTR_SW_WIRED) == 0) {
			/*
			 * Write protect the mapping to a single page so that
			 * a subsequent write access may repromote.
			 */
			va += VM_PAGE_TO_PHYS(m) - (oldl2 & ~ATTR_MASK);
			l3 = pmap_l2_to_l3(l2, va);
			oldl3 = pmap_load(l3);
			while (!atomic_fcmpset_long(l3, &oldl3,
			    (oldl3 & ~ATTR_SW_DBM) | ATTR_S1_AP(ATTR_S1_AP_RO)))
				cpu_spinwait();
			vm_page_dirty(m);
			pmap_invalidate_page(pmap, va);
		}
		PMAP_UNLOCK(pmap);
	}
	TAILQ_FOREACH(pv, &m->md.pv_list, pv_next) {