[src/trunk]: src/sys/uvm fix amap_extend() to handle amaps where we previousl...

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

details:   https://anonhg.NetBSD.org/src/rev/5293e5eef18c
branches:  trunk
changeset: 937424:5293e5eef18c
user:      chs <chs%NetBSD.org@localhost>
date:      Tue Aug 18 10:40:20 2020 +0000

description:
fix amap_extend() to handle amaps where we previously failed to allocate
the ppref memory.

diffstat:

 sys/uvm/uvm_amap.c |  36 +++++++++++++++++++++++++++++++++---
 1 files changed, 33 insertions(+), 3 deletions(-)

diffs (64 lines):

diff -r 6a8e949c3b5a -r 5293e5eef18c sys/uvm/uvm_amap.c
--- a/sys/uvm/uvm_amap.c        Tue Aug 18 10:35:51 2020 +0000
+++ b/sys/uvm/uvm_amap.c        Tue Aug 18 10:40:20 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: uvm_amap.c,v 1.122 2020/07/09 05:57:15 skrll Exp $     */
+/*     $NetBSD: uvm_amap.c,v 1.123 2020/08/18 10:40:20 chs Exp $       */
 
 /*
  * Copyright (c) 1997 Charles D. Cranor and Washington University.
@@ -35,7 +35,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: uvm_amap.c,v 1.122 2020/07/09 05:57:15 skrll Exp $");
+__KERNEL_RCSID(0, "$NetBSD: uvm_amap.c,v 1.123 2020/08/18 10:40:20 chs Exp $");
 
 #include "opt_uvmhist.h"
 
@@ -353,7 +353,7 @@
        struct vm_amap *amap = entry->aref.ar_amap;
        int slotoff = entry->aref.ar_pageoff;
        int slotmapped, slotadd, slotneed, slotadded, slotalloc;
-       int slotadj, slotarea;
+       int slotadj, slotarea, slotendoff;
        int oldnslots;
 #ifdef UVM_AMAP_PPREF
        int *newppref, *oldppref;
@@ -388,6 +388,36 @@
        }
 
        /*
+        * Because this amap only has 1 ref, we know that there is
+        * only one vm_map_entry pointing to it, and the one entry is
+        * using slots between slotoff and slotoff + slotmapped.  If
+        * we have been using ppref then we know that only slots in
+        * the one map entry's range can have anons, since ppref
+        * allowed us to free any anons outside that range as other map
+        * entries which used this amap were removed. But without ppref,
+        * we couldn't know which slots were still needed by other map
+        * entries, so we couldn't free any anons as we removed map
+        * entries, and so any slot from 0 to am_nslot can have an
+        * anon.  But now that we know there is only one map entry
+        * left and we know its range, we can free up any anons
+        * outside that range.  This is necessary because the rest of
+        * this function assumes that there are no anons in the amap
+        * outside of the one map entry's range.
+        */
+
+       slotendoff = slotoff + slotmapped;
+       if (amap->am_ppref == PPREF_NONE) {
+               amap_wiperange(amap, 0, slotoff);
+               amap_wiperange(amap, slotendoff, amap->am_nslot - slotendoff);
+       }
+       for (i = 0; i < slotoff; i++) {
+               KASSERT(amap->am_anon[i] == NULL);
+       }
+       for (i = slotendoff; i < amap->am_nslot - slotendoff; i++) {
+               KASSERT(amap->am_anon[i] == NULL);
+       }
+
+       /*
         * case 1: we already have enough slots in the map and thus
         * only need to bump the reference counts on the slots we are
         * adding.