[PATCH 1/2] x86: eliminate TS_XSAVE

Avi Kivity
2010-05-02T14:54:37Z

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.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
arch/x86/include/asm/i387.h | 20 ++++++++++++++++----
arch/x86/include/asm/thread_info.h | 1 -
arch/x86/kernel/cpu/common.c | 5 +----
arch/x86/kernel/i387.c | 5 +----
arch/x86/kernel/xsave.c | 6 +++---
5 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index da29309..52f95c0 100644
--- a/arch/x86/include/asm/i387.h
+++ b/arch/x86/include/asm/i387.h
@@ -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)
+{
+ bool has_xsave;
+
+ alternative_io("xor %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);
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index d017ed5..d4092fa 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -242,7 +242,6 @@ 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)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 4868e4a..c1c00d0 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -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();

diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index 54c31c2..14ca1dc 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -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 */
diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index 782c3a3..c1b0a11 100644
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -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 *)
--
1.7.0.4