In order to satisfy ACPI's need for an identity mapping, modify the

temporary mapping created by locore so that the lowest two to four
megabytes can become a permanent identity mapping.  This implementation
avoids any use of a large page mapping.

2 files changed, 40 insertions, 32 deletions

diff --git a/sys/i386/i386/locore.s b/sys/i386/i386/locore.s
index b789504..d922e11 100644
--- a/sys/i386/i386/locore.s
+++ b/sys/i386/i386/locore.s
@@ -777,21 +777,6 @@ no_kernend:
 	movl	%esi, R(SMPpt)		/* relocated to KVM space */
 #endif	/* SMP */
 
-/* Map page zero read-write so bios32 calls can use it */
-	xorl	%eax, %eax
-	movl	$PG_RW,%edx
-	movl	$1,%ecx
-	fillkptphys(%edx)
-
-/* Map read-only from page 1 to the beginning of the kernel text section */
-	movl	$PAGE_SIZE, %eax
-	xorl	%edx,%edx
-	movl	$R(btext),%ecx
-	addl	$PAGE_MASK,%ecx
-	subl	%eax,%ecx
-	shrl	$PAGE_SHIFT,%ecx
-	fillkptphys(%edx)
-
 /*
  * Enable PSE and PGE.
  */
@@ -815,22 +800,21 @@ no_kernend:
 #endif
 
 /*
- * Write page tables for the kernel starting at btext and
- * until the end.  Make sure to map read+write.  We do this even
+ * Initialize page table pages mapping physical address zero through the
+ * end of the kernel.  All of the page table entries allow read and write
+ * access.  Write access to the first physical page is required by bios32
+ * calls, and write access to the first 1 MB of physical memory is required
+ * by ACPI for implementing suspend and resume.  We do this even
  * if we've enabled PSE above, we'll just switch the corresponding kernel
  * PDEs before we turn on paging.
  *
  * XXX: We waste some pages here in the PSE case!  DON'T BLINDLY REMOVE
  * THIS!  SMP needs the page table to be there to map the kernel P==V.
  */
-	movl	$R(btext),%eax
-	addl	$PAGE_MASK, %eax
-	andl	$~PAGE_MASK, %eax
-	movl	$PG_RW,%edx
+	xorl	%eax, %eax
 	movl	R(KERNend),%ecx
-	subl	%eax,%ecx
 	shrl	$PAGE_SHIFT,%ecx
-	fillkptphys(%edx)
+	fillkptphys($PG_RW)
 
 /* Map page directory. */
 #ifdef PAE
@@ -901,11 +885,37 @@ no_kernend:
 	fillkpt(R(SMPptpa), $PG_RW)
 #endif	/* SMP */
 
-/* install a pde for temporary double map of bottom of VA */
+/*
+ * Create an identity mapping for low physical memory, including the kernel.
+ * The part of this mapping that covers the first 1 MB of physical memory
+ * becomes a permanent part of the kernel's address space.  The rest of this
+ * mapping is destroyed in pmap_bootstrap().  Ordinarily, the same page table
+ * pages are shared by the identity mapping and the kernel's native mapping.
+ * However, the permanent identity mapping cannot contain PG_G mappings.
+ * Thus, if the kernel is loaded within the permanent identity mapping, that
+ * page table page must be duplicated and not shared.
+ *
+ * N.B. Due to errata concerning large pages and physical address zero,
+ * a PG_PS mapping is not used.
+ */
 	movl	R(KPTphys), %eax
 	xorl	%ebx, %ebx
 	movl	$NKPT, %ecx
 	fillkpt(R(IdlePTD), $PG_RW)
+#if KERNLOAD < (1 << PDRSHIFT)
+	testl	$PG_G, R(pgeflag)
+	jz	1f
+	ALLOCPAGES(1)
+	movl	%esi, %edi
+	movl	R(IdlePTD), %eax
+	movl	(%eax), %esi
+	movl	%edi, (%eax)
+	movl	$PAGE_SIZE, %ecx
+	cld
+	rep
+	movsb
+1:	
+#endif
 
 /*
  * For the non-PSE case, install PDEs for PTs covering the KVA.
diff --git a/sys/i386/i386/pmap.c b/sys/i386/i386/pmap.c
index 19a18e9..a05d680 100644
--- a/sys/i386/i386/pmap.c
+++ b/sys/i386/i386/pmap.c
@@ -408,13 +408,18 @@ pmap_bootstrap(vm_paddr_t firstaddr)
 
 	*CMAP1 = 0;
 
+	/*
+	 * Leave in place an identity mapping (virt == phys) for the low 1 MB
+	 * physical memory region that is used by the ACPI wakeup code.  This
+	 * mapping must not have PG_G set. 
+	 */
 #ifdef XBOX
 	/* FIXME: This is gross, but needed for the XBOX. Since we are in such
 	 * an early stadium, we cannot yet neatly map video memory ... :-(
 	 * Better fixes are very welcome! */
 	if (!arch_i386_is_xbox)
 #endif
-	for (i = 0; i < NKPT; i++)
+	for (i = 1; i < NKPT; i++)
 		PTD[i] = 0;
 
 	/* Initialize the PAT MSR if present. */
@@ -422,13 +427,6 @@ pmap_bootstrap(vm_paddr_t firstaddr)
 
 	/* Turn on PG_G on kernel page(s) */
 	pmap_set_pg();
-
-	/*
-	 * Create an identity mapping (virt == phys) for the low 1 MB
-	 * physical memory region that is used by the ACPI wakeup code.
-	 * This mapping must not have PG_G set. 
-	 */
-	kernel_pmap->pm_pdir[0] = PG_PS | PG_RW | PG_V;
 }
 
 /*