[tip:x86/fpu] x86/fpu: Speed up lazy FPU restores slightly

[tip-bot for Andy Lutomirski]

Commit-ID:  c6ab109f7e0eae3bae3bb10f8ddb0df67735c150
Gitweb:     http://git.kernel.org/tip/c6ab109f7e0eae3bae3bb10f8ddb0df67735c150
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Sun, 24 Jan 2016 14:38:09 -0800
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 9 Feb 2016 15:42:56 +0100

x86/fpu: Speed up lazy FPU restores slightly

If we have an FPU, there's no need to check CR0 for FPU emulation.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Quentin Casasnovas <quentin.casasnovas@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: yu-cheng yu <yu-cheng.yu@xxxxxxxxx>
Link: http://lkml.kernel.org/r/980004297e233c27066d54e71382c44cdd36ef7c.1453675014.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/kernel/traps.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 87f80fe..36a9c01 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -752,7 +752,7 @@ do_device_not_available(struct pt_regs *regs, long error_code)
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 
 #ifdef CONFIG_MATH_EMULATION
-	if (read_cr0() & X86_CR0_EM) {
+	if (!boot_cpu_has(X86_FEATURE_FPU) && (read_cr0() & X86_CR0_EM)) {
 		struct math_emu_info info = { };
 
 		conditional_sti(regs);