[src/trunk]: src/sys/arch/xen/x86 Remove a few #if 0s, and explain what we ar...

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

details:   https://anonhg.NetBSD.org/src/rev/e52a5a85e7cb
branches:  trunk
changeset: 820290:e52a5a85e7cb
user:      maxv <maxv%NetBSD.org@localhost>
date:      Fri Jan 06 08:32:26 2017 +0000

description:
Remove a few #if 0s, and explain what we are doing on PAE: the last two PAs
are entered in reversed order.

diffstat:

 sys/arch/xen/x86/x86_xpmap.c |  52 ++++++++++++++++---------------------------
 1 files changed, 20 insertions(+), 32 deletions(-)

diffs (119 lines):

diff -r 59b5b6d2524b -r e52a5a85e7cb sys/arch/xen/x86/x86_xpmap.c
--- a/sys/arch/xen/x86/x86_xpmap.c      Fri Jan 06 08:05:26 2017 +0000
+++ b/sys/arch/xen/x86/x86_xpmap.c      Fri Jan 06 08:32:26 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: x86_xpmap.c,v 1.68 2016/12/16 19:52:22 maxv Exp $      */
+/*     $NetBSD: x86_xpmap.c,v 1.69 2017/01/06 08:32:26 maxv Exp $      */
 
 /*
  * Copyright (c) 2006 Mathieu Ropert <mro%adviseo.fr@localhost>
@@ -66,7 +66,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: x86_xpmap.c,v 1.68 2016/12/16 19:52:22 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: x86_xpmap.c,v 1.69 2017/01/06 08:32:26 maxv Exp $");
 
 #include "opt_xen.h"
 #include "opt_ddb.h"
@@ -664,7 +664,7 @@
                count++;
        }
 
-#ifndef __x86_64__
+#ifdef i386
        /*
         * One more L2 page: we'll allocate several pages after kva_start
         * in pmap_bootstrap() before pmap_growkernel(), which have not been
@@ -832,21 +832,24 @@
        pdtpe[pl3_pi(KERNTEXTOFF)] =
            xpmap_ptom_masked(addr) | PG_k | PG_V | PG_RW;
 #elif defined(PAE)
-       /* Our PAE-style level 2: 5 contigous pages (4 L2 + 1 shadow) */
+       /*
+        * Our PAE-style level 2, 5 contiguous pages (4 L2 + 1 shadow).
+        *                  +-----------------+----------------+---------+
+        * Physical layout: | 3 * USERLAND L2 | L2 KERN SHADOW | L2 KERN |
+        *                  +-----------------+----------------+---------+
+        * However, we enter pdtpte[3] into L2 KERN, and not L2 KERN SHADOW.
+        * This way, pde[L2_SLOT_KERN] always points to the shadow.
+        */
        pde = (pd_entry_t *)avail;
        memset(pde, 0, PAGE_SIZE * 5);
        avail += PAGE_SIZE * 5;
-       addr = ((u_long)pde) - KERNBASE;
 
        /*
-        * Enter L2 pages in L3. The real L2 kernel PD will be the last one
-        * (so that pde[L2_SLOT_KERN] always points to the shadow).
+        * Link L2 pages in L3, with a special case for L2 KERN. Xen doesn't
+        * want RW permissions in L3 entries, it'll add them itself.
         */
+       addr = ((u_long)pde) - KERNBASE;
        for (i = 0; i < 3; i++, addr += PAGE_SIZE) {
-               /*
-                * Xen doesn't want RW mappings in L3 entries, it'll add it
-                * itself.
-                */
                pdtpe[i] = xpmap_ptom_masked(addr) | PG_k | PG_V;
        }
        addr += PAGE_SIZE;
@@ -944,15 +947,11 @@
 
        /* Install recursive page tables mapping */
 #ifdef PAE
-       /*
-        * We need a shadow page for the kernel's L2 page.
-        * The real L2 kernel PD will be the last one (so that
-        * pde[L2_SLOT_KERN] always points to the shadow).
-        */
+       /* Copy L2 KERN into L2 KERN SHADOW, and reference the latter in cpu0. */
        memcpy(&pde[L2_SLOT_KERN + NPDPG], &pde[L2_SLOT_KERN], PAGE_SIZE);
        cpu_info_primary.ci_kpm_pdir = &pde[L2_SLOT_KERN + NPDPG];
        cpu_info_primary.ci_kpm_pdirpa =
-           (vaddr_t) cpu_info_primary.ci_kpm_pdir - KERNBASE;
+           (vaddr_t)cpu_info_primary.ci_kpm_pdir - KERNBASE;
 
        /*
         * We don't enter a recursive entry from the L3 PD. Instead, we enter
@@ -965,28 +964,16 @@
                pde[PDIR_SLOT_PTE + i] = xpmap_ptom_masked(addr) | PG_k | PG_V |
                    pg_nx;
        }
-#if 0
-       addr += PAGE_SIZE; /* point to shadow L2 */
-       pde[PDIR_SLOT_PTE + 3] = xpmap_ptom_masked(addr) | PG_k | PG_V;
-#endif
-       /* Mark tables RO, and pin the kernel's shadow as L2 */
+
+       /* Mark tables RO, and pin L2 KERN SHADOW. */
        addr = (u_long)pde - KERNBASE;
        for (i = 0; i < 5; i++, addr += PAGE_SIZE) {
                xen_bt_set_readonly(((vaddr_t)pde) + PAGE_SIZE * i);
-#if 0
-               if (i == 2 || i == 3)
-                       continue;
-               xpq_queue_pin_l2_table(xpmap_ptom_masked(addr));
-#endif
        }
        if (final) {
                addr = (u_long)pde - KERNBASE + 3 * PAGE_SIZE;
                xpq_queue_pin_l2_table(xpmap_ptom_masked(addr));
        }
-#if 0
-       addr = (u_long)pde - KERNBASE + 2 * PAGE_SIZE;
-       xpq_queue_pin_l2_table(xpmap_ptom_masked(addr));
-#endif
 #else /* PAE */
 
        /* Recursive entry in pmap_kernel(). */
@@ -1000,7 +987,8 @@
 
        /* Mark tables RO */
        xen_bt_set_readonly((vaddr_t)pde);
-#endif
+#endif /* PAE */
+
 #if PTP_LEVELS > 2 || defined(PAE)
        xen_bt_set_readonly((vaddr_t)pdtpe);
 #endif