[src/trunk]: src/sys/uvm uvmspace_exec(): set VM_MAP_DYING for the duration, ...

[ad <ad%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/ec5c34dff35a
branches:  trunk
changeset: 970999:ec5c34dff35a
user:      ad <ad%NetBSD.org@localhost>
date:      Fri Apr 10 17:26:46 2020 +0000

description:
uvmspace_exec(): set VM_MAP_DYING for the duration, so pmap_update() is not
called until the pmap has been totally cleared out after pmap_remove_all(),
or it can confuse some pmap implementations.

diffstat:

 sys/uvm/uvm_map.c |  23 +++++++++++++++++++----
 1 files changed, 19 insertions(+), 4 deletions(-)

diffs (55 lines):

diff -r adf2937afd52 -r ec5c34dff35a sys/uvm/uvm_map.c
--- a/sys/uvm/uvm_map.c Fri Apr 10 17:18:04 2020 +0000
+++ b/sys/uvm/uvm_map.c Fri Apr 10 17:26:46 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: uvm_map.c,v 1.377 2020/04/04 21:17:02 ad Exp $ */
+/*     $NetBSD: uvm_map.c,v 1.378 2020/04/10 17:26:46 ad Exp $ */
 
 /*
  * Copyright (c) 1997 Charles D. Cranor and Washington University.
@@ -66,7 +66,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: uvm_map.c,v 1.377 2020/04/04 21:17:02 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: uvm_map.c,v 1.378 2020/04/10 17:26:46 ad Exp $");
 
 #include "opt_ddb.h"
 #include "opt_pax.h"
@@ -2266,7 +2266,10 @@
 
                        /*
                         * note: if map is dying, leave pmap_update() for
-                        * pmap_destroy(), which will be called later.
+                        * later.  if the map is to be reused (exec) then
+                        * pmap_update() will be called.  if the map is
+                        * being disposed of (exit) then pmap_destroy()
+                        * will be called.
                         */
 
                        if ((map->flags & VM_MAP_DYING) == 0) {
@@ -4167,11 +4170,23 @@
                map->flags &= ~VM_MAP_WIREFUTURE;
 
                /*
-                * now unmap the old program
+                * now unmap the old program.
+                * 
+                * XXX set VM_MAP_DYING for the duration, so pmap_update()
+                * is not called until the pmap has been totally cleared out
+                * after pmap_remove_all(), or it can confuse some pmap
+                * implementations.  it would be nice to handle this by
+                * deferring the pmap_update() while it is known the address
+                * space is not visible to any user LWP other than curlwp,
+                * but there isn't an elegant way of inferring that right
+                * now.
                 */
 
                flags = pmap_remove_all(map->pmap) ? UVM_FLAG_VAONLY : 0;
+               map->flags |= VM_MAP_DYING;
                uvm_unmap1(map, vm_map_min(map), vm_map_max(map), flags);
+               map->flags &= ~VM_MAP_DYING;
+               pmap_update(map->pmap);
                KASSERT(map->header.prev == &map->header);
                KASSERT(map->nentries == 0);