[src/trunk]: src/sys/arch/amd64/stand/prekern Fix a mistake I made in the ver...

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

details:   https://anonhg.NetBSD.org/src/rev/5281da6ace71
branches:  trunk
changeset: 827448:5281da6ace71
user:      maxv <maxv%NetBSD.org@localhost>
date:      Sat Oct 28 19:28:11 2017 +0000

description:
Fix a mistake I made in the very first revision. The calculation of the
number of slots was incorrect in some cases, and it could cause the
prekern to fault right away at boot time, or the kernel to fault when
loading kernel modules near the end of the module map.

The variables are divided by PAGE_SIZE to prevent integer overflows.

diffstat:

 sys/arch/amd64/stand/prekern/mm.c |  22 +++++++++++++++-------
 1 files changed, 15 insertions(+), 7 deletions(-)

diffs (60 lines):

diff -r 33f118f648b7 -r 5281da6ace71 sys/arch/amd64/stand/prekern/mm.c
--- a/sys/arch/amd64/stand/prekern/mm.c Sat Oct 28 19:25:31 2017 +0000
+++ b/sys/arch/amd64/stand/prekern/mm.c Sat Oct 28 19:28:11 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: mm.c,v 1.4 2017/10/23 06:00:59 maxv Exp $      */
+/*     $NetBSD: mm.c,v 1.5 2017/10/28 19:28:11 maxv Exp $      */
 
 /*
  * Copyright (c) 2017 The NetBSD Foundation, Inc. All rights reserved.
@@ -112,20 +112,28 @@
        }
 }
 
+static size_t
+mm_nentries_range(vaddr_t startva, vaddr_t endva, size_t pgsz)
+{
+       size_t npages;
+
+       npages = roundup((endva / PAGE_SIZE), (pgsz / PAGE_SIZE)) -
+           rounddown((startva / PAGE_SIZE), (pgsz / PAGE_SIZE));
+       return (npages / (pgsz / PAGE_SIZE));
+}
+
 static void
 mm_map_tree(vaddr_t startva, vaddr_t endva)
 {
-       size_t i, size, nL4e, nL3e, nL2e;
+       size_t i, nL4e, nL3e, nL2e;
        size_t L4e_idx, L3e_idx, L2e_idx;
        paddr_t pa;
 
-       size = endva - startva;
-
        /*
         * Build L4.
         */
        L4e_idx = pl4_i(startva);
-       nL4e = roundup(size, NBPD_L4) / NBPD_L4;
+       nL4e = mm_nentries_range(startva, endva, NBPD_L4);
        ASSERT(L4e_idx == 511);
        ASSERT(nL4e == 1);
        if (!mm_pte_is_valid(L4_BASE[L4e_idx])) {
@@ -137,7 +145,7 @@
         * Build L3.
         */
        L3e_idx = pl3_i(startva);
-       nL3e = roundup(size, NBPD_L3) / NBPD_L3;
+       nL3e = mm_nentries_range(startva, endva, NBPD_L3);
        for (i = 0; i < nL3e; i++) {
                if (mm_pte_is_valid(L3_BASE[L3e_idx+i])) {
                        continue;
@@ -150,7 +158,7 @@
         * Build L2.
         */
        L2e_idx = pl2_i(startva);
-       nL2e = roundup(size, NBPD_L2) / NBPD_L2;
+       nL2e = mm_nentries_range(startva, endva, NBPD_L2);
        for (i = 0; i < nL2e; i++) {
                if (mm_pte_is_valid(L2_BASE[L2e_idx+i])) {
                        continue;