patch lower-case-segops
remove xhat
The xhat infrastructure was added to support hardware such as the zulu
graphics card - hardware which had on-board MMUs.  The VM used the xhat code
to keep the CPU's and Zulu's page tables in-sync.  Since the only xhat user
was zulu (which is gone), we can safely remove it simplifying the whole VM
subsystem.
Assorted notes:
- AS_BUSY flag was used solely by xhat

*** 180,194 ****
                  return (0);
  
          /*
           * as->a_wpage can only be changed while the process is totally stopped.
           * Don't grab p_lock here.  Holding p_lock while grabbing the address
!          * space lock leads to deadlocks with the clock thread.  Note that if an
!          * as_fault() is servicing a fault to a watched page on behalf of an
!          * XHAT provider, watchpoint will be temporarily cleared (and wp_prot
!          * will be set to wp_oprot).  Since this is done while holding as writer
!          * lock, we need to grab as lock (reader lock is good enough).
           *
           * p_maplock prevents simultaneous execution of this function.  Under
           * normal circumstances, holdwatch() will stop all other threads, so the
           * lock isn't really needed.  But there may be multiple threads within
           * stop() when SWATCHOK is set, so we need to handle multiple threads
--- 180,190 ----
                  return (0);
  
          /*
           * as->a_wpage can only be changed while the process is totally stopped.
           * Don't grab p_lock here.  Holding p_lock while grabbing the address
!          * space lock leads to deadlocks with the clock thread.
           *
           * p_maplock prevents simultaneous execution of this function.  Under
           * normal circumstances, holdwatch() will stop all other threads, so the
           * lock isn't really needed.  But there may be multiple threads within
           * stop() when SWATCHOK is set, so we need to handle multiple threads
*** 309,321 ****
                          AS_LOCK_EXIT(as, &as->a_lock);
                          AS_LOCK_ENTER(as, &as->a_lock, RW_WRITER);
                  retry:
                          seg = as_segat(as, addr);
                          ASSERT(seg != NULL);
!                         SEGOP_GETPROT(seg, addr, 0, &oprot);
                          if (prot != oprot) {
!                                 err = SEGOP_SETPROT(seg, addr, PAGESIZE, prot);
                                  if (err == IE_RETRY) {
                                          ASSERT(retrycnt == 0);
                                          retrycnt++;
                                          goto retry;
                                  }
--- 305,317 ----
                          AS_LOCK_EXIT(as, &as->a_lock);
                          AS_LOCK_ENTER(as, &as->a_lock, RW_WRITER);
                  retry:
                          seg = as_segat(as, addr);
                          ASSERT(seg != NULL);
!                         segop_getprot(seg, addr, 0, &oprot);
                          if (prot != oprot) {
!                                 err = segop_setprot(seg, addr, PAGESIZE, prot);
                                  if (err == IE_RETRY) {
                                          ASSERT(retrycnt == 0);
                                          retrycnt++;
                                          goto retry;
                                  }
*** 404,414 ****
          retry:
                  ASSERT(pwp->wp_flags & WP_SETPROT);
                  if ((seg = as_segat(as, vaddr)) != NULL &&
                      !(pwp->wp_flags & WP_NOWATCH)) {
                          prot = pwp->wp_prot;
!                         err = SEGOP_SETPROT(seg, vaddr, PAGESIZE, prot);
                          if (err == IE_RETRY) {
                                  ASSERT(retrycnt == 0);
                                  retrycnt++;
                                  goto retry;
                          }
--- 400,410 ----
          retry:
                  ASSERT(pwp->wp_flags & WP_SETPROT);
                  if ((seg = as_segat(as, vaddr)) != NULL &&
                      !(pwp->wp_flags & WP_NOWATCH)) {
                          prot = pwp->wp_prot;
!                         err = segop_setprot(seg, vaddr, PAGESIZE, prot);
                          if (err == IE_RETRY) {
                                  ASSERT(retrycnt == 0);
                                  retrycnt++;
                                  goto retry;
                          }
*** 502,512 ****
          int rv;
  
          if ((as == &kas) || avl_numnodes(&as->a_wpage) == 0)
                  return (0);
  
-         /* Grab the lock because of XHAT (see comment in pr_mappage()) */
          AS_LOCK_ENTER(as, &as->a_lock, RW_READER);
          rv = pr_is_watchpage_as(addr, rw, as);
          AS_LOCK_EXIT(as, &as->a_lock);
  
          return (rv);
--- 498,507 ----