diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index f5376676f89c7..a850b4d8d14d9 100644
--- a/arch/x86/include/asm/i387.h
+++ b/arch/x86/include/asm/i387.h
@@ -29,6 +29,7 @@ extern unsigned int sig_xstate_size;
extern void fpu_init(void);
extern void mxcsr_feature_mask_init(void);
extern int init_fpu(struct task_struct *child);
+extern void __math_state_restore(struct task_struct *);
extern void math_state_restore(void);
extern int dump_fpu(struct pt_regs *, struct user_i387_struct *);
@@ -212,9 +213,10 @@ static inline void fpu_fxsave(struct fpu *fpu)
#endif /* CONFIG_X86_64 */
/*
- * These must be called with preempt disabled
+ * These must be called with preempt disabled. Returns
+ * 'true' if the FPU state is still intact.
*/
-static inline void fpu_save_init(struct fpu *fpu)
+static inline int fpu_save_init(struct fpu *fpu)
{
if (use_xsave()) {
fpu_xsave(fpu);
@@ -223,22 +225,33 @@ static inline void fpu_save_init(struct fpu *fpu)
* xsave header may indicate the init state of the FP.
*/
if (!(fpu->state->xsave.xsave_hdr.xstate_bv & XSTATE_FP))
- return;
+ return 1;
} else if (use_fxsr()) {
fpu_fxsave(fpu);
} else {
asm volatile("fnsave %[fx]; fwait"
: [fx] "=m" (fpu->state->fsave));
- return;
+ return 0;
}
- if (unlikely(fpu->state->fxsave.swd & X87_FSW_ES))
+ /*
+ * If exceptions are pending, we need to clear them so
+ * that we don't randomly get exceptions later.
+ *
+ * FIXME! Is this perhaps only true for the old-style
+ * irq13 case? Maybe we could leave the x87 state
+ * intact otherwise?
+ */
+ if (unlikely(fpu->state->fxsave.swd & X87_FSW_ES)) {
asm volatile("fnclex");
+ return 0;
+ }
+ return 1;
}
-static inline void __save_init_fpu(struct task_struct *tsk)
+static inline int __save_init_fpu(struct task_struct *tsk)
{
- fpu_save_init(&tsk->thread.fpu);
+ return fpu_save_init(&tsk->thread.fpu);
}
static inline int fpu_fxrstor_checking(struct fpu *fpu)
@@ -301,20 +314,79 @@ static inline void __thread_fpu_begin(struct task_struct *tsk)
}
/*
- * Signal frame handlers...
+ * FPU state switching for scheduling.
+ *
+ * This is a two-stage process:
+ *
+ * - switch_fpu_prepare() saves the old state and
+ * sets the new state of the CR0.TS bit. This is
+ * done within the context of the old process.
+ *
+ * - switch_fpu_finish() restores the new state as
+ * necessary.
*/
-extern int save_i387_xstate(void __user *buf);
-extern int restore_i387_xstate(void __user *buf);
+typedef struct { int preload; } fpu_switch_t;
+
+/*
+ * FIXME! We could do a totally lazy restore, but we need to
+ * add a per-cpu "this was the task that last touched the FPU
+ * on this CPU" variable, and the task needs to have a "I last
+ * touched the FPU on this CPU" and check them.
+ *
+ * We don't do that yet, so "fpu_lazy_restore()" always returns
+ * false, but some day..
+ */
+#define fpu_lazy_restore(tsk) (0)
+#define fpu_lazy_state_intact(tsk) do { } while (0)
+
+static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct task_struct *new)
+{
+ fpu_switch_t fpu;
+
+ fpu.preload = tsk_used_math(new) && new->fpu_counter > 5;
+ if (__thread_has_fpu(old)) {
+ if (__save_init_fpu(old))
+ fpu_lazy_state_intact(old);
+ __thread_clear_has_fpu(old);
+ old->fpu_counter++;
+
+ /* Don't change CR0.TS if we just switch! */
+ if (fpu.preload) {
+ __thread_set_has_fpu(new);
+ prefetch(new->thread.fpu.state);
+ } else
+ stts();
+ } else {
+ old->fpu_counter = 0;
+ if (fpu.preload) {
+ if (fpu_lazy_restore(new))
+ fpu.preload = 0;
+ else
+ prefetch(new->thread.fpu.state);
+ __thread_fpu_begin(new);
+ }
+ }
+ return fpu;
+}
-static inline void __unlazy_fpu(struct task_struct *tsk)
+/*
+ * By the time this gets called, we've already cleared CR0.TS and
+ * given the process the FPU if we are going to preload the FPU
+ * state - all we need to do is to conditionally restore the register
+ * state itself.
+ */
+static inline void switch_fpu_finish(struct task_struct *new, fpu_switch_t fpu)
{
- if (__thread_has_fpu(tsk)) {
- __save_init_fpu(tsk);
- __thread_fpu_end(tsk);
- } else
- tsk->fpu_counter = 0;
+ if (fpu.preload)
+ __math_state_restore(new);
}
+/*
+ * Signal frame handlers...
+ */
+extern int save_i387_xstate(void __user *buf);
+extern int restore_i387_xstate(void __user *buf);
+
static inline void __clear_fpu(struct task_struct *tsk)
{
if (__thread_has_fpu(tsk)) {
@@ -474,7 +546,11 @@ static inline void save_init_fpu(struct task_struct *tsk)
static inline void unlazy_fpu(struct task_struct *tsk)
{
preempt_disable();
- __unlazy_fpu(tsk);
+ if (__thread_has_fpu(tsk)) {
+ __save_init_fpu(tsk);
+ __thread_fpu_end(tsk);
+ } else
+ tsk->fpu_counter = 0;
preempt_enable();
}
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 0cdb4fa541248..8598296140852 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -297,10 +297,11 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
*next = &next_p->thread;
int cpu = smp_processor_id();
struct tss_struct *tss = &per_cpu(init_tss, cpu);
+ fpu_switch_t fpu;
/* never put a printk in __switch_to... printk() calls wake_up*() indirectly */
- __unlazy_fpu(prev_p);
+ fpu = switch_fpu_prepare(prev_p, next_p);
/*
* Reload esp0.
@@ -355,6 +356,8 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
if (prev->gs | next->gs)
lazy_load_gs(next->gs);
+ switch_fpu_finish(next_p, fpu);
+
percpu_write(current_task, next_p);
return prev_p;
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 042b18f3716e0..6a364a67e2b7d 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -381,8 +381,9 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
int cpu = smp_processor_id();
struct tss_struct *tss = &per_cpu(init_tss, cpu);
unsigned fsindex, gsindex;
+ fpu_switch_t fpu;
- __unlazy_fpu(prev_p);
+ fpu = switch_fpu_prepare(prev_p, next_p);
/*
* Reload esp0, LDT and the page table pointer:
@@ -452,6 +453,8 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
wrmsrl(MSR_KERNEL_GS_BASE, next->gs);
prev->gsindex = gsindex;
+ switch_fpu_finish(next_p, fpu);
+
/*
* Switch the PDA and FPU contexts.
*/
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index a99badf2fe819..31d9d0f04c2b0 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -561,6 +561,37 @@ asmlinkage void __attribute__((weak)) smp_threshold_interrupt(void)
{
}
+/*
+ * This gets called with the process already owning the
+ * FPU state, and with CR0.TS cleared. It just needs to
+ * restore the FPU register state.
+ */
+void __math_state_restore(struct task_struct *tsk)
+{
+ /* We need a safe address that is cheap to find and that is already
+ in L1. We've just brought in "tsk->thread.has_fpu", so use that */
+#define safe_address (tsk->thread.has_fpu)
+
+ /* 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 */
+ alternative_input(
+ ASM_NOP8 ASM_NOP2,
+ "emms\n\t" /* clear stack tags */
+ "fildl %P[addr]", /* set F?P to defined value */
+ X86_FEATURE_FXSAVE_LEAK,
+ [addr] "m" (safe_address));
+
+ /*
+ * Paranoid restore. send a SIGSEGV if we fail to restore the state.
+ */
+ if (unlikely(restore_fpu_checking(tsk))) {
+ __thread_fpu_end(tsk);
+ force_sig(SIGSEGV, tsk);
+ return;
+ }
+}
+
/*
* 'math_state_restore()' saves the current math information in the
* old math state array, and gets the new ones from the current task
@@ -575,10 +606,6 @@ void math_state_restore(void)
{
struct task_struct *tsk = current;
- /* We need a safe address that is cheap to find and that is already
- in L1. We're just bringing in "tsk->thread.has_fpu", so use that */
-#define safe_address (tsk->thread.has_fpu)
-
if (!tsk_used_math(tsk)) {
local_irq_enable();
/*
@@ -595,25 +622,7 @@ void math_state_restore(void)
}
__thread_fpu_begin(tsk);
-
- /* 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 */
- alternative_input(
- ASM_NOP8 ASM_NOP2,
- "emms\n\t" /* clear stack tags */
- "fildl %P[addr]", /* set F?P to defined value */
- X86_FEATURE_FXSAVE_LEAK,
- [addr] "m" (safe_address));
-
- /*
- * Paranoid restore. send a SIGSEGV if we fail to restore the state.
- */
- if (unlikely(restore_fpu_checking(tsk))) {
- __thread_fpu_end(tsk);
- force_sig(SIGSEGV, tsk);
- return;
- }
+ __math_state_restore(tsk);
tsk->fpu_counter++;
}