x86, 64-bit: Set data segments to null after switching to 64-bit mode

This prevents kernel threads from inheriting non-null segment
selectors, and causing optimizations in __switch_to() to be
ineffective.

Signed-off-by: Brian Gerst <[email protected]>
Cc: Tim Blechmann <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Jeremy Fitzhardinge <[email protected]>
Cc: Jan Beulich <[email protected]>
LKML-Reference: <1259165856[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 26406601031c9a3a3b6ee54cbf112f2599a42633..17ba9ecf27c5072aeece45e3f34ba3e0c7cc1afc 100644 (file)
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -212,8 +212,8 @@ ENTRY(secondary_startup_64)
         */
        lgdt    early_gdt_descr(%rip)
 
-       /* set up data segments. actually 0 would do too */
-       movl $__KERNEL_DS,%eax
+       /* set up data segments */
+       xorl %eax,%eax
        movl %eax,%ds
        movl %eax,%ss
        movl %eax,%es