x86-32: use brk segment for allocating initial kernel pagetable

Impact: use new interface instead of previous ad hoc implementation

Rather than having special purpose init_pg_table_start/end variables
to delimit the kernel pagetable built by head_32.S, just use the brk
mechanism to extend the bss for the new pagetable.

This patch removes init_pg_table_start/end and pg0, defines __brk_base
(which is page-aligned and immediately follows _end), initializes
the brk region to start there, and uses it for the 32-bit pagetable.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

4 files changed, 7 insertions, 20 deletions

diff --git a/arch/x86/kernel/head32.c b/arch/x86/kernel/head32.c
index 29f1095b084..3f8579f8d42 100644
--- a/arch/x86/kernel/head32.c
+++ b/arch/x86/kernel/head32.c
@@ -29,9 +29,6 @@ void __init i386_start_kernel(void)
 		reserve_early(ramdisk_image, ramdisk_end, "RAMDISK");
 	}
 #endif
-	reserve_early(init_pg_tables_start, init_pg_tables_end,
-			"INIT_PG_TABLE");
-
 	reserve_ebda_region();
 
 	/*
diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index c32ca19d591..db6652710e9 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -167,7 +167,7 @@ num_subarch_entries = (. - subarch_entries) / 4
 /*
  * Initialize page tables.  This creates a PDE and a set of page
  * tables, which are located immediately beyond _end.  The variable
- * init_pg_tables_end is set up to point to the first "safe" location.
+ * _brk_end is set up to point to the first "safe" location.
  * Mappings are created both at virtual address 0 (identity mapping)
  * and PAGE_OFFSET for up to _end+sizeof(page tables)+INIT_MAP_BEYOND_END.
  *
@@ -190,8 +190,7 @@ default_entry:
 
 	xorl %ebx,%ebx				/* %ebx is kept at zero */
 
-	movl $pa(pg0), %edi
-	movl %edi, pa(init_pg_tables_start)
+	movl $pa(__brk_base), %edi
 	movl $pa(swapper_pg_pmd), %edx
 	movl $PTE_IDENT_ATTR, %eax
 10:
@@ -216,7 +215,8 @@ default_entry:
 	cmpl %ebp,%eax
 	jb 10b
 1:
-	movl %edi,pa(init_pg_tables_end)
+	addl $__PAGE_OFFSET, %edi
+	movl %edi, pa(_brk_end)
 	shrl $12, %eax
 	movl %eax, pa(max_pfn_mapped)
 
@@ -227,8 +227,7 @@ default_entry:
 
 page_pde_offset = (__PAGE_OFFSET >> 20);
 
-	movl $pa(pg0), %edi
-	movl %edi, pa(init_pg_tables_start)
+	movl $pa(__brk_base), %edi
 	movl $pa(swapper_pg_dir), %edx
 	movl $PTE_IDENT_ATTR, %eax
 10:
@@ -249,7 +248,8 @@ page_pde_offset = (__PAGE_OFFSET >> 20);
 	leal (INIT_MAP_BEYOND_END+PTE_IDENT_ATTR)(%edi),%ebp
 	cmpl %ebp,%eax
 	jb 10b
-	movl %edi,pa(init_pg_tables_end)
+	addl $__PAGE_OFFSET, %edi
+	movl %edi, pa(_brk_end)
 	shrl $12, %eax
 	movl %eax, pa(max_pfn_mapped)
 
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index b8329029c15..3ac2aa7b9ea 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -161,12 +161,6 @@ static struct resource bss_resource = {
 
 
 #ifdef CONFIG_X86_32
-/* This value is set up by the early boot code to point to the value
-   immediately after the boot time page tables.  It contains a *physical*
-   address, and must not be in the .bss segment! */
-unsigned long init_pg_tables_start __initdata = ~0UL;
-unsigned long init_pg_tables_end __initdata = ~0UL;
-
 static struct resource video_ram_resource = {
 	.name	= "Video RAM area",
 	.start	= 0xa0000,
diff --git a/arch/x86/kernel/vmlinux_32.lds.S b/arch/x86/kernel/vmlinux_32.lds.S
index 27e44aa2158..1063fbe93c7 100644
--- a/arch/x86/kernel/vmlinux_32.lds.S
+++ b/arch/x86/kernel/vmlinux_32.lds.S
@@ -196,10 +196,6 @@ SECTIONS
 	__brk_limit = . ;
 
   	_end = . ;
-
-	/* This is where the kernel creates the early boot page tables */
-	. = ALIGN(PAGE_SIZE);
-	pg0 = . ;
   }
 
   /* Sections to be discarded */