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>
diff --git a/include/asm-x86/i387.h b/include/asm-x86/i387.h
index 6a66478..a6d256f 100644
--- a/include/asm-x86/i387.h
+++ b/include/asm-x86/i387.h
@@ -36,6 +36,8 @@
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 @@
_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 @@
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 @@
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 @@
: "=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 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 __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 @@
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 @@
"fildl %[addr]", /* set F?P to defined value */
X86_FEATURE_FXSAVE_LEAK,
[addr] "m" (safe_address));
+end:
task_thread_info(tsk)->status &= ~TS_USEDFPU;
}