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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>
This commit is contained in:
Suresh Siddha 2008-07-29 10:29:20 -07:00 committed by Ingo Molnar
parent dc1e35c6e9
commit b359e8a434
7 changed files with 103 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
arch/x86/kernel/cpu/common.c
View File

@ -709,6 +709,9 @@ void __cpuinit cpu_init(void)
/*
* Force FPU initialization:
*/
if (cpu_has_xsave)
current_thread_info()->status = TS_XSAVE;
else
current_thread_info()->status = 0;
clear_used_math();
mxcsr_feature_mask_init();

3
arch/x86/kernel/i387.c
View File

@ -97,6 +97,9 @@ 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;
clear_used_math();
}

2
arch/x86/kernel/traps_64.c
View File

@ -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;

64
include/asm-x86/i387.h
View File

@ -36,6 +36,8 @@ extern int save_i387_ia32(struct _fpstate_ia32 __user *buf);
extern int restore_i387_ia32(struct _fpstate_ia32 __user *buf);
#endif
#define X87_FSW_ES (1 << 7) /* Exception Summary */
#ifdef CONFIG_X86_64
/* Ignore delayed exceptions from user space */
@ -46,7 +48,7 @@ static inline void tolerant_fwait(void)
_ASM_EXTABLE(1b, 2b));
}
static inline int restore_fpu_checking(struct i387_fxsave_struct *fx)
static inline int fxrstor_checking(struct i387_fxsave_struct *fx)
{
int err;
@ -66,15 +68,31 @@ static inline int restore_fpu_checking(struct i387_fxsave_struct *fx)
return err;
}
#define X87_FSW_ES (1 << 7) /* Exception Summary */
static inline int restore_fpu_checking(struct task_struct *tsk)
{
if (task_thread_info(tsk)->status & TS_XSAVE)
return xrstor_checking(&tsk->thread.xstate->xsave);
else
return fxrstor_checking(&tsk->thread.xstate->fxsave);
}
/* AMD CPUs don't save/restore FDP/FIP/FOP unless an exception
is pending. Clear the x87 state here by setting it to fixed
values. The kernel data segment can be sometimes 0 and sometimes
new user value. Both should be ok.
Use the PDA as safe address because it should be already in L1. */
static inline void clear_fpu_state(struct i387_fxsave_struct *fx)
static inline void clear_fpu_state(struct task_struct *tsk)
{
struct xsave_struct *xstate = &tsk->thread.xstate->xsave;
struct i387_fxsave_struct *fx = &tsk->thread.xstate->fxsave;
/*
* xsave header may indicate the init state of the FP.
*/
if ((task_thread_info(tsk)->status & TS_XSAVE) &&
!(xstate->xsave_hdr.xstate_bv & XSTATE_FP))
return;
if (unlikely(fx->swd & X87_FSW_ES))
asm volatile("fnclex");
alternative_input(ASM_NOP8 ASM_NOP2,
@ -107,7 +125,7 @@ static inline int save_i387_checking(struct i387_fxsave_struct __user *fx)
return err;
}
static inline void __save_init_fpu(struct task_struct *tsk)
static inline void fxsave(struct task_struct *tsk)
{
/* Using "rex64; fxsave %0" is broken because, if the memory operand
uses any extended registers for addressing, a second REX prefix
@ -132,7 +150,16 @@ static inline void __save_init_fpu(struct task_struct *tsk)
: "=m" (tsk->thread.xstate->fxsave)
: "cdaSDb" (&tsk->thread.xstate->fxsave));
#endif
clear_fpu_state(&tsk->thread.xstate->fxsave);
}
static inline void __save_init_fpu(struct task_struct *tsk)
{
if (task_thread_info(tsk)->status & TS_XSAVE)
xsave(tsk);
else
fxsave(tsk);
clear_fpu_state(tsk);
task_thread_info(tsk)->status &= ~TS_USEDFPU;
}
@ -147,6 +174,10 @@ static inline void tolerant_fwait(void)
static inline void restore_fpu(struct task_struct *tsk)
{
if (task_thread_info(tsk)->status & TS_XSAVE) {
xrstor_checking(&tsk->thread.xstate->xsave);
return;
}
/*
* The "nop" is needed to make the instructions the same
* length.
@ -172,6 +203,27 @@ static inline void restore_fpu(struct task_struct *tsk)
*/
static inline void __save_init_fpu(struct task_struct *tsk)
{
if (task_thread_info(tsk)->status & TS_XSAVE) {
struct xsave_struct *xstate = &tsk->thread.xstate->xsave;
struct i387_fxsave_struct *fx = &tsk->thread.xstate->fxsave;
xsave(tsk);
/*
* xsave header may indicate the init state of the FP.
*/
if (!(xstate->xsave_hdr.xstate_bv & XSTATE_FP))
goto end;
if (unlikely(fx->swd & X87_FSW_ES))
asm volatile("fnclex");
/*
* we can do a simple return here or be paranoid :)
*/
goto clear_state;
}
/* Use more nops than strictly needed in case the compiler
varies code */
alternative_input(
@ -181,6 +233,7 @@ static inline void __save_init_fpu(struct task_struct *tsk)
X86_FEATURE_FXSR,
[fx] "m" (tsk->thread.xstate->fxsave),
[fsw] "m" (tsk->thread.xstate->fxsave.swd) : "memory");
clear_state:
/* AMD K7/K8 CPUs don't save/restore FDP/FIP/FOP unless an exception
is pending. Clear the x87 state here by setting it to fixed
values. safe_address is a random variable that should be in L1 */
@ -190,6 +243,7 @@ static inline void __save_init_fpu(struct task_struct *tsk)
"fildl %[addr]", /* set F?P to defined value */
X86_FEATURE_FXSAVE_LEAK,
[addr] "m" (safe_address));
end:
task_thread_info(tsk)->status &= ~TS_USEDFPU;
}

1
include/asm-x86/processor.h
View File

@ -362,6 +362,7 @@ union thread_xstate {
struct i387_fsave_struct fsave;
struct i387_fxsave_struct fxsave;
struct i387_soft_struct soft;
struct xsave_struct xsave;
};
#ifdef CONFIG_X86_64

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

@ -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)

33
include/asm-x86/xsave.h
View File

@ -17,10 +17,43 @@
#define XCNTXT_LMASK (XSTATE_FP | XSTATE_SSE)
#define XCNTXT_HMASK 0x0
#ifdef CONFIG_X86_64
#define REX_PREFIX "0x48, "
#else
#define REX_PREFIX
#endif
extern unsigned int xstate_size, pcntxt_hmask, pcntxt_lmask;
extern struct xsave_struct *init_xstate_buf;
extern void xsave_cntxt_init(void);
extern void xsave_init(void);
extern int init_fpu(struct task_struct *child);
static inline int xrstor_checking(struct xsave_struct *fx)
{
int err;
asm volatile("1: .byte " REX_PREFIX "0x0f,0xae,0x2f\n\t"
"2:\n"
".section .fixup,\"ax\"\n"
"3: movl $-1,%[err]\n"
" jmp 2b\n"
".previous\n"
_ASM_EXTABLE(1b, 3b)
: [err] "=r" (err)
: "D" (fx), "m" (*fx), "a" (-1), "d" (-1), "0" (0)
: "memory");
return err;
}
static inline void xsave(struct task_struct *tsk)
{
/* This, however, we can work around by forcing the compiler to select
an addressing mode that doesn't require extended registers. */
__asm__ __volatile__(".byte " REX_PREFIX "0x0f,0xae,0x27"
: : "D" (&(tsk->thread.xstate->xsave)),
"a" (-1), "d"(-1) : "memory");
}
#endif