From 1ea0d14e480c245683927eecc03a70faf06e80c8 Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Thu, 3 Sep 2009 12:27:15 -0700 Subject: x86/i386: Make sure stack-protector segment base is cache aligned The Intel Optimization Reference Guide says: In Intel Atom microarchitecture, the address generation unit assumes that the segment base will be 0 by default. Non-zero segment base will cause load and store operations to experience a delay. - If the segment base isn't aligned to a cache line boundary, the max throughput of memory operations is reduced to one [e]very 9 cycles. [...] Assembly/Compiler Coding Rule 15. (H impact, ML generality) For Intel Atom processors, use segments with base set to 0 whenever possible; avoid non-zero segment base address that is not aligned to cache line boundary at all cost. We can't avoid having a non-zero base for the stack-protector segment, but we can make it cache-aligned. Signed-off-by: Jeremy Fitzhardinge Cc: LKML-Reference: <4AA01893.6000507@goop.org> Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/common.c | 2 +- arch/x86/kernel/head_32.S | 1 - 2 files changed, 1 insertion(+), 2 deletions(-) (limited to 'arch/x86/kernel') diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index ced07ba..7d84bc4 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/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(unsigned long, stack_canary); +DEFINE_PER_CPU(struct stack_canary, stack_canary) ____cacheline_aligned; #endif /* Make sure %fs and %gs are initialized properly in idle threads */ diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S index cc827ac..7ffec6b 100644 --- a/arch/x86/kernel/head_32.S +++ b/arch/x86/kernel/head_32.S @@ -439,7 +439,6 @@ is386: movl $2,%ecx # set MP jne 1f movl $per_cpu__gdt_page,%eax movl $per_cpu__stack_canary,%ecx - subl $20, %ecx movw %cx, 8 * GDT_ENTRY_STACK_CANARY + 2(%eax) shrl $16, %ecx movb %cl, 8 * GDT_ENTRY_STACK_CANARY + 4(%eax) -- cgit v1.1