Function pmap_remove_write

freebsd/amd64/amd64/pmap.c:8326–8410

* Clear the write and modified bits in each of the given page's mappings. */

 * Clear the write and modified bits in each of the given page's mappings.
 */
void
pmap_remove_write(vm_page_t m)
{
	struct md_page *pvh;
	pmap_t pmap;
	struct rwlock *lock;
	pv_entry_t next_pv, pv;
	pd_entry_t *pde;
	pt_entry_t oldpte, *pte, PG_M, PG_RW;
	vm_offset_t va;
	int pvh_gen, md_gen;

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

	vm_page_assert_busied(m);
	if (!pmap_page_is_write_mapped(m))
		return;

	lock = VM_PAGE_TO_PV_LIST_LOCK(m);
	pvh = (m->flags & PG_FICTITIOUS) != 0 ? &pv_dummy :
	    pa_to_pvh(VM_PAGE_TO_PHYS(m));
retry_pv_loop:
	rw_wlock(lock);
	TAILQ_FOREACH_SAFE(pv, &pvh->pv_list, pv_next, next_pv) {
		pmap = PV_PMAP(pv);
		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);
				rw_wunlock(lock);
				goto retry_pv_loop;
			}
		}
		PG_RW = pmap_rw_bit(pmap);
		va = pv->pv_va;
		pde = pmap_pde(pmap, va);
		if ((*pde & PG_RW) != 0)
			(void)pmap_demote_pde_locked(pmap, pde, va, &lock);
		KASSERT(lock == VM_PAGE_TO_PV_LIST_LOCK(m),
		    ("inconsistent pv lock %p %p for page %p",
		    lock, VM_PAGE_TO_PV_LIST_LOCK(m), m));
		PMAP_UNLOCK(pmap);
	}
	TAILQ_FOREACH(pv, &m->md.pv_list, pv_next) {
		pmap = PV_PMAP(pv);
		if (!PMAP_TRYLOCK(pmap)) {
			pvh_gen = pvh->pv_gen;
			md_gen = m->md.pv_gen;
			rw_wunlock(lock);
			PMAP_LOCK(pmap);
			rw_wlock(lock);
			if (pvh_gen != pvh->pv_gen ||
			    md_gen != m->md.pv_gen) {
				PMAP_UNLOCK(pmap);