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>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/asm-x86/thread_info.h b/include/asm-x86/thread_info.h
index e64be8863b76..30586f2ee558 100644
--- a/include/asm-x86/thread_info.h
+++ b/include/asm-x86/thread_info.h
@@ -239,6 +239,7 @@ static inline struct thread_info *stack_thread_info(void)
 #define TS_POLLING              0x0004  /* true if in idle loop
                                            and not sleeping */
 #define TS_RESTORE_SIGMASK      0x0008  /* restore signal mask in do_signal() */
+#define TS_XSAVE                0x0010  /* Use xsave/xrstor */
 
 #define tsk_is_polling(t) (task_thread_info(t)->status & TS_POLLING)