x86, xsave: context switch support using xsave/xrstor

Uses xsave/xrstor (instead of traditional fxsave/fxrstor) in context switch
when available.

Introduces TS_XSAVE flag, which determine the need to use xsave/xrstor
instructions during context switch instead of the legacy fxsave/fxrstor
instructions. Thread-synchronous status word is already in L1 cache during
this code patch and thus minimizes the performance penality compared to
(cpu_has_xsave) checks.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 9 insertions, 3 deletions

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index fabbcb7020fb..6c2b9e756db2 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -709,7 +709,10 @@ void __cpuinit cpu_init(void)
         /*
          * Force FPU initialization:
          */
-        current_thread_info()->status = 0;
+        if (cpu_has_xsave)
+                current_thread_info()->status = TS_XSAVE;
+        else
+                current_thread_info()->status = 0;
         clear_used_math();
         mxcsr_feature_mask_init();
 
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index e22a9a9dce8a..b778e17e4b01 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -97,7 +97,10 @@ void __cpuinit fpu_init(void)
 
         mxcsr_feature_mask_init();
         /* clean state in init */
-        current_thread_info()->status = 0;
+        if (cpu_has_xsave)
+                current_thread_info()->status = TS_XSAVE;
+        else
+                current_thread_info()->status = 0;
         clear_used_math();
 }
 #endif  /* CONFIG_X86_64 */
diff --git a/arch/x86/kernel/traps_64.c b/arch/x86/kernel/traps_64.c
index 3580a7938a2e..38eb76156a47 100644
--- a/arch/x86/kernel/traps_64.c
+++ b/arch/x86/kernel/traps_64.c
@@ -1134,7 +1134,7 @@ asmlinkage void math_state_restore(void)
         /*
          * Paranoid restore. send a SIGSEGV if we fail to restore the state.
          */
-        if (unlikely(restore_fpu_checking(&me->thread.xstate->fxsave))) {
+        if (unlikely(restore_fpu_checking(me))) {
                 stts();
                 force_sig(SIGSEGV, me);
                 return;