SEG_DESC_PRESENT
if (SEG_DESC_UNUSABLE(access) || !SEG_DESC_PRESENT(access))
assert(SEG_DESC_PRESENT(desc->access));
if (!SEG_DESC_PRESENT(nt.access)) {
assert(!SEG_DESC_UNUSABLE(access) && SEG_DESC_PRESENT(access));
KASSERT(SEG_DESC_PRESENT(desc->access),