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Subject[PATCH 3/4] x86, fpu: Let the fpu remember which cpu it is active on
Date
Add a member fpu->cpu to struct fpu which contains which cpu has this fpu
register set loaded (or -1 if the registers were flushed to memory in
fpu->state).

The various fpu accesors are modified to IPI the loaded cpu if it
happens to be different from the current cpu.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
arch/x86/include/asm/i387.h | 115 +++++++++++++++++++++++++++++++++++--
arch/x86/include/asm/processor.h | 4 +
arch/x86/kernel/i387.c | 3 +
arch/x86/kernel/process.c | 1 +
4 files changed, 116 insertions(+), 7 deletions(-)
diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index df5badf..124c89d 100644
--- a/arch/x86/include/asm/i387.h
+++ b/arch/x86/include/asm/i387.h
@@ -174,7 +174,7 @@ static inline void fpu_fxsave(struct fpu *fpu)
#endif
}

-static inline void fpu_save_init(struct fpu *fpu)
+static inline void __fpu_save_init(struct fpu *fpu)
{
if (use_xsave())
fpu_xsave(fpu);
@@ -222,10 +222,7 @@ static inline int fxrstor_checking(struct i387_fxsave_struct *fx)
#define safe_address (kstat_cpu(0).cpustat.user)
#endif

-/*
- * These must be called with preempt disabled
- */
-static inline void fpu_save_init(struct fpu *fpu)
+static inline void __fpu_save_init(struct fpu *fpu)
{
if (use_xsave()) {
struct xsave_struct *xstate = &fpu->state->xsave;
@@ -273,6 +270,33 @@ end:

#endif /* CONFIG_X86_64 */

+static inline bool fpu_loaded(struct fpu *fpu)
+{
+ return fpu->cpu == smp_processor_id();
+}
+
+static inline bool fpu_remote(struct fpu *fpu)
+{
+ return fpu->cpu != -1 && fpu->cpu != smp_processor_id();
+}
+
+/*
+ * These must be called with preempt disabled
+ */
+static inline void fpu_save_init(struct fpu *fpu)
+{
+ ulong flags;
+
+ if (__get_cpu_var(current_fpu) != fpu
+ || fpu->cpu != smp_processor_id())
+ return;
+ local_irq_save(flags);
+ __fpu_save_init(fpu);
+ fpu->cpu = -1;
+ __get_cpu_var(current_fpu) = NULL;
+ local_irq_restore(flags);
+}
+
static inline void __save_init_fpu(struct task_struct *tsk)
{
fpu_save_init(&tsk->thread.fpu);
@@ -284,7 +308,7 @@ static inline int fpu_fxrstor_checking(struct fpu *fpu)
return fxrstor_checking(&fpu->state->fxsave);
}

-static inline int fpu_restore_checking(struct fpu *fpu)
+static inline int __fpu_restore_checking(struct fpu *fpu)
{
if (use_xsave())
return fpu_xrstor_checking(fpu);
@@ -292,6 +316,47 @@ static inline int fpu_restore_checking(struct fpu *fpu)
return fpu_fxrstor_checking(fpu);
}

+static inline void __fpu_unload(void *_fpu)
+{
+ struct fpu *fpu = _fpu;
+ unsigned cr0 = read_cr0();
+
+ if (cr0 & X86_CR0_TS)
+ clts();
+ if (__get_cpu_var(current_fpu) == fpu)
+ fpu_save_init(fpu);
+ if (cr0 & X86_CR0_TS)
+ write_cr0(cr0);
+}
+
+static inline void fpu_unload(struct fpu *fpu)
+{
+ int cpu = ACCESS_ONCE(fpu->cpu);
+
+ if (cpu != -1)
+ smp_call_function_single(cpu, __fpu_unload, fpu, 1);
+}
+
+static inline int fpu_restore_checking(struct fpu *fpu)
+{
+ ulong flags;
+ struct fpu *oldfpu;
+ int ret;
+
+ if (fpu->cpu == smp_processor_id())
+ return 0;
+ fpu_unload(fpu);
+ local_irq_save(flags);
+ oldfpu = __get_cpu_var(current_fpu);
+ if (oldfpu)
+ fpu_save_init(oldfpu);
+ ret = __fpu_restore_checking(fpu);
+ fpu->cpu = smp_processor_id();
+ __get_cpu_var(current_fpu) = fpu;
+ local_irq_restore(flags);
+ return ret;
+}
+
static inline int restore_fpu_checking(struct task_struct *tsk)
{
return fpu_restore_checking(&tsk->thread.fpu);
@@ -451,18 +516,46 @@ static bool fpu_allocated(struct fpu *fpu)
return fpu->state != NULL;
}

+static inline void fpu_init_empty(struct fpu *fpu)
+{
+ fpu->state = NULL;
+ fpu->cpu = -1;
+}
+
static inline int fpu_alloc(struct fpu *fpu)
{
if (fpu_allocated(fpu))
return 0;
fpu->state = kmem_cache_alloc(task_xstate_cachep, GFP_KERNEL);
+ fpu->cpu = -1;
if (!fpu->state)
return -ENOMEM;
WARN_ON((unsigned long)fpu->state & 15);
return 0;
}

-static inline void fpu_free(struct fpu *fpu)
+static inline void __fpu_forget(void *_fpu)
+{
+ struct fpu *fpu = _fpu;
+
+ if (fpu->cpu == smp_processor_id()) {
+ fpu->cpu = -1;
+ __get_cpu_var(current_fpu) = NULL;
+ }
+}
+
+static inline void fpu_forget(struct fpu *fpu)
+{
+ int cpu;
+
+ preempt_disable();
+ cpu = ACCESS_ONCE(fpu->cpu);
+ if (cpu != -1)
+ smp_call_function_single(cpu, __fpu_forget, fpu, 1);
+ preempt_enable();
+}
+
+static inline void __fpu_free(struct fpu *fpu)
{
if (fpu->state) {
kmem_cache_free(task_xstate_cachep, fpu->state);
@@ -470,8 +563,16 @@ static inline void fpu_free(struct fpu *fpu)
}
}

+static inline void fpu_free(struct fpu *fpu)
+{
+ fpu_forget(fpu);
+ __fpu_free(fpu);
+}
+
static inline void fpu_copy(struct fpu *dst, struct fpu *src)
{
+ fpu_unload(src);
+ fpu_unload(dst);
memcpy(dst->state, src->state, xstate_size);
}

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 7e5c6a6..98996fe 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -378,8 +378,11 @@ union thread_xstate {

struct fpu {
union thread_xstate *state;
+ int cpu; /* -1 = unloaded */
};

+DECLARE_PER_CPU(struct fpu *, current_fpu);
+
#ifdef CONFIG_X86_64
DECLARE_PER_CPU(struct orig_ist, orig_ist);

@@ -892,6 +895,7 @@ static inline void spin_lock_prefetch(const void *x)
.vm86_info = NULL, \
.sysenter_cs = __KERNEL_CS, \
.io_bitmap_ptr = NULL, \
+ .fpu = { .cpu = -1, }, \
}

/*
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index c4444bc..e56f486 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -38,6 +38,9 @@
# define HAVE_HWFP 1
#endif

+DEFINE_PER_CPU(struct fpu *, current_fpu);
+EXPORT_PER_CPU_SYMBOL_GPL(current_fpu);
+
static unsigned int mxcsr_feature_mask __read_mostly = 0xffffffffu;
unsigned int xstate_size;
unsigned int sig_xstate_ia32_size = sizeof(struct _fpstate_ia32);
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index ebcfcce..16a7a9b 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -35,6 +35,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
int ret;

*dst = *src;
+ fpu_init_empty(&dst->thread.fpu);
if (fpu_allocated(&src->thread.fpu)) {
memset(&dst->thread.fpu, 0, sizeof(dst->thread.fpu));
ret = fpu_alloc(&dst->thread.fpu);
--
1.7.1


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