Function _pmap_alloc_l3

freebsd/arm64/arm64/pmap.c:1846–1969

* This routine is called if the desired page table page does not exist. * * If page table page allocation fails, this routine may sleep before * returning NULL. It sleeps only if a lock pointer was given. * * Note: If a page allocation fails at page table level two or three, * one or two pages may be held during the wait, only to be released * afterwards. This conservative approach is eas

 * race conditions.
 */
static vm_page_t
_pmap_alloc_l3(pmap_t pmap, vm_pindex_t ptepindex, struct rwlock **lockp)
{
	vm_page_t m, l1pg, l2pg;

	PMAP_LOCK_ASSERT(pmap, MA_OWNED);

	/*
	 * Allocate a page table page.
	 */
	if ((m = vm_page_alloc(NULL, ptepindex, VM_ALLOC_NOOBJ |
	    VM_ALLOC_WIRED | VM_ALLOC_ZERO)) == NULL) {
		if (lockp != NULL) {
			RELEASE_PV_LIST_LOCK(lockp);
			PMAP_UNLOCK(pmap);
			vm_wait(NULL);
			PMAP_LOCK(pmap);
		}

		/*
		 * Indicate the need to retry.  While waiting, the page table
		 * page may have been allocated.
		 */
		return (NULL);
	}
	if ((m->flags & PG_ZERO) == 0)
		pmap_zero_page(m);

	/*
	 * Because of AArch64's weak memory consistency model, we must have a
	 * barrier here to ensure that the stores for zeroing "m", whether by
	 * pmap_zero_page() or an earlier function, are visible before adding
	 * "m" to the page table.  Otherwise, a page table walk by another
	 * processor's MMU could see the mapping to "m" and a stale, non-zero
	 * PTE within "m".
	 */
	dmb(ishst);

	/*
	 * Map the pagetable page into the process address space, if
	 * it isn't already there.
	 */

	if (ptepindex >= (NUL2E + NUL1E)) {
		pd_entry_t *l0;
		vm_pindex_t l0index;

		l0index = ptepindex - (NUL2E + NUL1E);
		l0 = &pmap->pm_l0[l0index];
		pmap_store(l0, VM_PAGE_TO_PHYS(m) | L0_TABLE);
	} else if (ptepindex >= NUL2E) {
		vm_pindex_t l0index, l1index;
		pd_entry_t *l0, *l1;
		pd_entry_t tl0;

		l1index = ptepindex - NUL2E;
		l0index = l1index >> L0_ENTRIES_SHIFT;