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x86: Eliminate TS_XSAVE 

The fpu code currently uses current->thread_info->status & TS_XSAVE as
a way to distinguish between XSAVE capable processors and older processors.
The decision is not really task specific; instead we use the task status to
avoid a global memory reference - the value should be the same across all
threads.

Eliminate this tie-in into the task structure by using an alternative
instruction keyed off the XSAVE cpu feature; this results in shorter and
faster code, without introducing a global memory reference.

[ hpa: in the future, this probably should use an asm jmp ]

Signed-off-by: Avi Kivity <avi@redhat.com>
Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <1273135546-29690-2-git-send-email-avi@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Avi Kivity 2010-05-06 11:45:45 +03:00 committed by H. Peter Anvin
parent 250825008f
commit c9ad488289
5 changed files with 21 additions and 16 deletions
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20
arch/x86/include/asm/i387.h
View File

@ -56,6 +56,18 @@ extern int restore_i387_xstate_ia32(void __user *buf);
#define X87_FSW_ES (1 << 7) /* Exception Summary */
static inline bool use_xsave(void)
{
u8 has_xsave;
alternative_io("mov $0, %0",
"mov $1, %0",
X86_FEATURE_XSAVE,
"=g"(has_xsave));
return has_xsave;
}
#ifdef CONFIG_X86_64
/* Ignore delayed exceptions from user space */
@ -99,7 +111,7 @@ static inline void clear_fpu_state(struct task_struct *tsk)
/*
* xsave header may indicate the init state of the FP.
*/
if ((task_thread_info(tsk)->status & TS_XSAVE) &&
if (use_xsave() &&
!(xstate->xsave_hdr.xstate_bv & XSTATE_FP))
return;
@ -164,7 +176,7 @@ static inline void fxsave(struct task_struct *tsk)
static inline void __save_init_fpu(struct task_struct *tsk)
{
if (task_thread_info(tsk)->status & TS_XSAVE)
if (use_xsave())
xsave(tsk);
else
fxsave(tsk);
@ -218,7 +230,7 @@ static inline int fxrstor_checking(struct i387_fxsave_struct *fx)
*/
static inline void __save_init_fpu(struct task_struct *tsk)
{
if (task_thread_info(tsk)->status & TS_XSAVE) {
if (use_xsave()) {
struct xsave_struct *xstate = &tsk->thread.xstate->xsave;
struct i387_fxsave_struct *fx = &tsk->thread.xstate->fxsave;
@ -266,7 +278,7 @@ end:
static inline int restore_fpu_checking(struct task_struct *tsk)
{
if (task_thread_info(tsk)->status & TS_XSAVE)
if (use_xsave())
return xrstor_checking(&tsk->thread.xstate->xsave);
else
return fxrstor_checking(&tsk->thread.xstate->fxsave);

1
arch/x86/include/asm/thread_info.h
View File

@ -244,7 +244,6 @@ static inline struct thread_info *current_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)

5
arch/x86/kernel/cpu/common.c
View File

@ -1243,10 +1243,7 @@ void __cpuinit cpu_init(void)
/*
* Force FPU initialization:
*/
if (cpu_has_xsave)
current_thread_info()->status = TS_XSAVE;
else
current_thread_info()->status = 0;
current_thread_info()->status = 0;
clear_used_math();
mxcsr_feature_mask_init();

5
arch/x86/kernel/i387.c
View File

@ -102,10 +102,7 @@ void __cpuinit fpu_init(void)
mxcsr_feature_mask_init();
/* clean state in init */
if (cpu_has_xsave)
current_thread_info()->status = TS_XSAVE;
else
current_thread_info()->status = 0;
current_thread_info()->status = 0;
clear_used_math();
}
#endif /* CONFIG_X86_64 */

6
arch/x86/kernel/xsave.c
View File

@ -99,7 +99,7 @@ int save_i387_xstate(void __user *buf)
if (err)
return err;
if (task_thread_info(tsk)->status & TS_XSAVE)
if (use_xsave())
err = xsave_user(buf);
else
err = fxsave_user(buf);
@ -116,7 +116,7 @@ int save_i387_xstate(void __user *buf)
clear_used_math(); /* trigger finit */
if (task_thread_info(tsk)->status & TS_XSAVE) {
if (use_xsave()) {
struct _fpstate __user *fx = buf;
struct _xstate __user *x = buf;
u64 xstate_bv;
@ -225,7 +225,7 @@ int restore_i387_xstate(void __user *buf)
clts();
task_thread_info(current)->status |= TS_USEDFPU;
}
if (task_thread_info(tsk)->status & TS_XSAVE)
if (use_xsave())
err = restore_user_xstate(buf);
else
err = fxrstor_checking((__force struct i387_fxsave_struct *)