x86/i386: Put aligned stack-canary in percpu shared_aligned section

Pack aligned things together into a special section to minimize
padding holes.

Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Tejun Heo <tj@kernel.org>
LKML-Reference: <4AA035C0.9070202@goop.org>
[ queued up in tip:x86/asm because it depends on this commit:
  x86/i386: Make sure stack-protector segment base is cache aligned ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/processor.h

@@ -413,7 +413,7 @@ struct stack_canary {
 	char __pad[20];		/* canary at %gs:20 */
 	unsigned long canary;
 };
-DECLARE_PER_CPU(struct stack_canary, stack_canary) ____cacheline_aligned;
+DECLARE_PER_CPU_ALIGNED(struct stack_canary, stack_canary);
 #endif
 #endif	/* X86_64 */
 

arch/x86/kernel/cpu/common.c

@@ -1043,7 +1043,7 @@ DEFINE_PER_CPU(struct orig_ist, orig_ist);
 #else	/* CONFIG_X86_64 */
 
 #ifdef CONFIG_CC_STACKPROTECTOR
-DEFINE_PER_CPU(struct stack_canary, stack_canary) ____cacheline_aligned;
+DEFINE_PER_CPU_ALIGNED(struct stack_canary, stack_canary);
 #endif
 
 /* Make sure %fs and %gs are initialized properly in idle threads */

include/asm-generic/percpu.h

@@ -81,14 +81,17 @@ extern void setup_per_cpu_areas(void);
 
 #ifdef MODULE
 #define PER_CPU_SHARED_ALIGNED_SECTION ""
+#define PER_CPU_ALIGNED_SECTION ""
 #else
 #define PER_CPU_SHARED_ALIGNED_SECTION ".shared_aligned"
+#define PER_CPU_ALIGNED_SECTION ".shared_aligned"
 #endif
 #define PER_CPU_FIRST_SECTION ".first"
 
 #else
 
 #define PER_CPU_SHARED_ALIGNED_SECTION ""
+#define PER_CPU_ALIGNED_SECTION ".shared_aligned"
 #define PER_CPU_FIRST_SECTION ""
 
 #endif

include/linux/percpu-defs.h

@@ -66,6 +66,14 @@
 	DEFINE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 	____cacheline_aligned_in_smp
 
+#define DECLARE_PER_CPU_ALIGNED(type, name)				\
+	DECLARE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)	\
+	____cacheline_aligned
+
+#define DEFINE_PER_CPU_ALIGNED(type, name)				\
+	DEFINE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)	\
+	____cacheline_aligned
+
 /*
  * Declaration/definition used for per-CPU variables that must be page aligned.
  */