x86, boot: straighten out ranges to copy/zero in compressed/head*.S

Both on 32 and 64 bits, we copy all the way up to the end of bss,
except that on 64 bits there is a hack to avoid copying on top of the
page tables.  There is no point in copying bss at all, especially
since we are just about to zero it all anyway.

To clean up and unify the handling, we now do:

  - copy from startup_32 to _bss.
  - zero from _bss to _ebss.
  - the _ebss symbol is aligned to an 8-byte boundary.
  - the page tables are moved to a separate section.

Use _bss as the copy endpoint since _edata may be misaligned.

[ Impact: cleanup, trivial performance improvement ]

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

3 files changed, 29 insertions, 16 deletions

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 7bd7766ffabf..59425e157df3 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -93,9 +93,9 @@ ENTRY(startup_32)
  * where decompression in place becomes safe.
  */
         pushl   %esi
-        leal    _ebss(%ebp), %esi
-        leal    _ebss(%ebx), %edi
-        movl    $(_ebss - startup_32), %ecx
+        leal    _bss(%ebp), %esi
+        leal    _bss(%ebx), %edi
+        movl    $(_bss - startup_32), %ecx
         std
         rep     movsb
         cld
@@ -125,7 +125,7 @@ relocated:
  * Clear BSS
  */
         xorl    %eax, %eax
-        leal    _edata(%ebx), %edi
+        leal    _bss(%ebx), %edi
         leal    _ebss(%ebx), %ecx
         subl    %edi, %ecx
         cld
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 26c3def43ace..5bc9052615b6 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -253,9 +253,9 @@ ENTRY(startup_64)
  * Copy the compressed kernel to the end of our buffer
  * where decompression in place becomes safe.
  */
-        leaq    _end_before_pgt(%rip), %r8
-        leaq    _end_before_pgt(%rbx), %r9
-        movq    $_end_before_pgt /* - $startup_32 */, %rcx
+        leaq    _bss(%rip), %r8
+        leaq    _bss(%rbx), %r9
+        movq    $_bss /* - $startup_32 */, %rcx
 1:      subq    $8, %r8
         subq    $8, %r9
         movq    0(%r8), %rax
@@ -276,8 +276,8 @@ relocated:
  * Clear BSS
  */
         xorq    %rax, %rax
-        leaq    _edata(%rbx), %rdi
-        leaq    _end_before_pgt(%rbx), %rcx
+        leaq    _bss(%rbx), %rdi
+        leaq    _ebss(%rbx), %rcx
         subq    %rdi, %rcx
         cld
         rep     stosb
@@ -329,3 +329,11 @@ boot_heap:
 boot_stack:
         .fill BOOT_STACK_SIZE, 1, 0
 boot_stack_end:
+
+/*
+ * Space for page tables (not in .bss so not zeroed)
+ */
+        .section ".pgtable","a",@nobits
+        .balign 4096
+pgtable:
+        .fill 6*4096, 1, 0
diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index dbe515e13fef..cc353e1b3ffd 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -2,6 +2,8 @@ OUTPUT_FORMAT(CONFIG_OUTPUT_FORMAT, CONFIG_OUTPUT_FORMAT, CONFIG_OUTPUT_FORMAT)
 
 #undef i386
 
+#include <asm/page_types.h>
+
 #ifdef CONFIG_X86_64
 OUTPUT_ARCH(i386:x86-64)
 ENTRY(startup_64)
@@ -48,13 +50,16 @@ SECTIONS
                 *(.bss)
                 *(.bss.*)
                 *(COMMON)
-#ifdef CONFIG_X86_64
-                . = ALIGN(8);
-                _end_before_pgt = . ;
-                . = ALIGN(4096);
-                pgtable = . ;
-                . = . + 4096 * 6;
-#endif
+                . = ALIGN(8);   /* For convenience during zeroing */
                 _ebss = .;
         }
+#ifdef CONFIG_X86_64
+       . = ALIGN(PAGE_SIZE);
+       .pgtable : {
+                _pgtable = . ;
+                *(.pgtable)
+                _epgtable = . ;
+        }
+#endif
+        _end = .;
 }