[PATCH 2/8] x86: Naturally align the debug IST stack

[Andi Kleen <andi@firstfloor.org>]

From: Andi Kleen <ak@linux.intel.com>

The followon patch for RD*BASE requires the IST stacks to be naturally
aligned because it uses and to access the bottom of the stack.
This was true for everyone except for the debug ist stack.
Make the debug ist stack naturally aligned too.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 arch/x86/include/asm/page_64_types.h | 4 ++--
 arch/x86/kernel/cpu/common.c         | 8 +++++++-
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
index 4edd53b..b631f04 100644
--- a/arch/x86/include/asm/page_64_types.h
+++ b/arch/x86/include/asm/page_64_types.h
@@ -22,8 +22,8 @@
 
 #define DOUBLEFAULT_STACK 1
 #define NMI_STACK 2
-#define DEBUG_STACK 3
-#define MCE_STACK 4
+#define MCE_STACK 3
+#define DEBUG_STACK 4 /* must be always last */
 #define N_EXCEPTION_STACKS 4  /* hw limit: 7 */
 
 #define PUD_PAGE_SIZE		(_AC(1, UL) << PUD_SHIFT)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 2346c95..33a0293 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1158,8 +1158,12 @@ static const unsigned int exception_stack_sizes[N_EXCEPTION_STACKS] = {
 	  [DEBUG_STACK - 1]			= DEBUG_STKSZ
 };
 
+/* The IST stacks must be naturally aligned */
+
 static DEFINE_PER_CPU_PAGE_ALIGNED(char, exception_stacks
-	[(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ + DEBUG_STKSZ]);
+	[(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ]);
+static DEFINE_PER_CPU_2PAGE_ALIGNED(char, debug_stack
+	[DEBUG_STKSZ]);
 
 /* May not be marked __init: used by software suspend */
 void syscall_init(void)
@@ -1349,6 +1353,8 @@ void cpu_init(void)
 		char *estacks = per_cpu(exception_stacks, cpu);
 
 		for (v = 0; v < N_EXCEPTION_STACKS; v++) {
+			if (v == DEBUG_STACK - 1)
+				estacks = per_cpu(debug_stack, cpu);
 			estacks += exception_stack_sizes[v];
 			oist->ist[v] = t->x86_tss.ist[v] =
 					(unsigned long)estacks;
-- 
1.9.3