Function pmap_protect

freebsd/amd64/amd64/pmap.c:6312–6470

* Set the physical protection on the * specified range of this map as requested. */

 *	specified range of this map as requested.
 */
void
pmap_protect(pmap_t pmap, vm_offset_t sva, vm_offset_t eva, vm_prot_t prot)
{
	vm_page_t m;
	vm_offset_t va_next;
	pml4_entry_t *pml4e;
	pdp_entry_t *pdpe;
	pd_entry_t ptpaddr, *pde;
	pt_entry_t *pte, PG_G, PG_M, PG_RW, PG_V;
	pt_entry_t obits, pbits;
	boolean_t anychanged;

	KASSERT((prot & ~VM_PROT_ALL) == 0, ("invalid prot %x", prot));
	if (prot == VM_PROT_NONE) {
		pmap_remove(pmap, sva, eva);
		return;
	}

	if ((prot & (VM_PROT_WRITE|VM_PROT_EXECUTE)) ==
	    (VM_PROT_WRITE|VM_PROT_EXECUTE))
		return;

	PG_G = pmap_global_bit(pmap);
	PG_M = pmap_modified_bit(pmap);
	PG_V = pmap_valid_bit(pmap);
	PG_RW = pmap_rw_bit(pmap);
	anychanged = FALSE;

	/*
	 * Although this function delays and batches the invalidation
	 * of stale TLB entries, it does not need to call
	 * pmap_delayed_invl_start() and
	 * pmap_delayed_invl_finish(), because it does not
	 * ordinarily destroy mappings.  Stale TLB entries from
	 * protection-only changes need only be invalidated before the
	 * pmap lock is released, because protection-only changes do
	 * not destroy PV entries.  Even operations that iterate over
	 * a physical page's PV list of mappings, like
	 * pmap_remove_write(), acquire the pmap lock for each
	 * mapping.  Consequently, for protection-only changes, the
	 * pmap lock suffices to synchronize both page table and TLB
	 * updates.
	 *
	 * This function only destroys a mapping if pmap_demote_pde()
	 * fails.  In that case, stale TLB entries are immediately
	 * invalidated.
	 */

	PMAP_LOCK(pmap);
	for (; sva < eva; sva = va_next) {
		pml4e = pmap_pml4e(pmap, sva);
		if (pml4e == NULL || (*pml4e & PG_V) == 0) {
			va_next = (sva + NBPML4) & ~PML4MASK;
			if (va_next < sva)
				va_next = eva;
			continue;
		}