x86, fpu: lazy allocation of FPU area - v5

Only allocate the FPU area when the application actually uses FPU, i.e., in the
first lazy FPU trap. This could save memory for non-fpu using apps.

for example: on my system after boot, there are around 300 processes, with
only 17 using FPU.
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/i387.c

@@ -8,7 +8,6 @@
 #include <linux/module.h>
 #include <linux/regset.h>
 #include <linux/sched.h>
-#include <linux/bootmem.h>
 
 #include <asm/sigcontext.h>
 #include <asm/processor.h>
@@ -63,7 +62,6 @@ void __init init_thread_xstate(void)
 	else
 		xstate_size = sizeof(struct i387_fsave_struct);
 #endif
-	init_task.thread.xstate = alloc_bootmem(xstate_size);
 }
 
 #ifdef CONFIG_X86_64
@@ -93,12 +91,22 @@ void __cpuinit fpu_init(void)
  * value at reset if we support XMM instructions and then
  * remeber the current task has used the FPU.
  */
-void init_fpu(struct task_struct *tsk)
+int init_fpu(struct task_struct *tsk)
 {
 	if (tsk_used_math(tsk)) {
 		if (tsk == current)
 			unlazy_fpu(tsk);
-		return;
+		return 0;
+	}
+
+	/*
+	 * Memory allocation at the first usage of the FPU and other state.
+	 */
+	if (!tsk->thread.xstate) {
+		tsk->thread.xstate = kmem_cache_alloc(task_xstate_cachep,
+						      GFP_KERNEL);
+		if (!tsk->thread.xstate)
+			return -ENOMEM;
 	}
 
 	if (cpu_has_fxsr) {
@@ -120,6 +128,7 @@ void init_fpu(struct task_struct *tsk)
 	 * Only the device not available exception or ptrace can call init_fpu.
 	 */
 	set_stopped_child_used_math(tsk);
+	return 0;
 }
 
 int fpregs_active(struct task_struct *target, const struct user_regset *regset)
@@ -136,10 +145,14 @@ int xfpregs_get(struct task_struct *target, const struct user_regset *regset,
 		unsigned int pos, unsigned int count,
 		void *kbuf, void __user *ubuf)
 {
+	int ret;
+
 	if (!cpu_has_fxsr)
 		return -ENODEV;
 
-	init_fpu(target);
+	ret = init_fpu(target);
+	if (ret)
+		return ret;
 
 	return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
 				   &target->thread.xstate->fxsave, 0, -1);
@@ -154,7 +167,10 @@ int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
 	if (!cpu_has_fxsr)
 		return -ENODEV;
 
-	init_fpu(target);
+	ret = init_fpu(target);
+	if (ret)
+		return ret;
+
 	set_stopped_child_used_math(target);
 
 	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
@@ -312,11 +328,14 @@ int fpregs_get(struct task_struct *target, const struct user_regset *regset,
 	       void *kbuf, void __user *ubuf)
 {
 	struct user_i387_ia32_struct env;
+	int ret;
 
 	if (!HAVE_HWFP)
 		return fpregs_soft_get(target, regset, pos, count, kbuf, ubuf);
 
-	init_fpu(target);
+	ret = init_fpu(target);
+	if (ret)
+		return ret;
 
 	if (!cpu_has_fxsr) {
 		return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
@@ -344,7 +363,10 @@ int fpregs_set(struct task_struct *target, const struct user_regset *regset,
 	if (!HAVE_HWFP)
 		return fpregs_soft_set(target, regset, pos, count, kbuf, ubuf);
 
-	init_fpu(target);
+	ret = init_fpu(target);
+	if (ret)
+		return ret;
+
 	set_stopped_child_used_math(target);
 
 	if (!cpu_has_fxsr) {

arch/x86/kernel/process.c

@@ -5,24 +5,34 @@
 #include <linux/slab.h>
 #include <linux/sched.h>
 
-static struct kmem_cache *task_xstate_cachep;
+struct kmem_cache *task_xstate_cachep;
 
 int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 {
 	*dst = *src;
-	dst->thread.xstate = kmem_cache_alloc(task_xstate_cachep, GFP_KERNEL);
+	if (src->thread.xstate) {
+		dst->thread.xstate = kmem_cache_alloc(task_xstate_cachep,
+						      GFP_KERNEL);
 		if (!dst->thread.xstate)
 			return -ENOMEM;
 		WARN_ON((unsigned long)dst->thread.xstate & 15);
 		memcpy(dst->thread.xstate, src->thread.xstate, xstate_size);
+	}
 	return 0;
 }
 
-void free_thread_info(struct thread_info *ti)
+void free_thread_xstate(struct task_struct *tsk)
 {
-	kmem_cache_free(task_xstate_cachep, ti->task->thread.xstate);
-	ti->task->thread.xstate = NULL;
+	if (tsk->thread.xstate) {
+		kmem_cache_free(task_xstate_cachep, tsk->thread.xstate);
+		tsk->thread.xstate = NULL;
+	}
+}
+
 
+void free_thread_info(struct thread_info *ti)
+{
+	free_thread_xstate(ti->task);
 	free_pages((unsigned long)(ti), get_order(THREAD_SIZE));
 }
 

arch/x86/kernel/process_32.c

@@ -521,6 +521,10 @@ start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
 	regs->cs		= __USER_CS;
 	regs->ip		= new_ip;
 	regs->sp		= new_sp;
+	/*
+	 * Free the old FP and other extended state
+	 */
+	free_thread_xstate(current);
 }
 EXPORT_SYMBOL_GPL(start_thread);
 

arch/x86/kernel/process_64.c

@@ -533,6 +533,10 @@ start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
 	regs->ss		= __USER_DS;
 	regs->flags		= 0x200;
 	set_fs(USER_DS);
+	/*
+	 * Free the old FP and other extended state
+	 */
+	free_thread_xstate(current);
 }
 EXPORT_SYMBOL_GPL(start_thread);
 

arch/x86/kernel/traps_32.c

@@ -1148,9 +1148,22 @@ asmlinkage void math_state_restore(void)
 	struct thread_info *thread = current_thread_info();
 	struct task_struct *tsk = thread->task;
 
+	if (!tsk_used_math(tsk)) {
+		local_irq_enable();
+		/*
+		 * does a slab alloc which can sleep
+		 */
+		if (init_fpu(tsk)) {
+			/*
+			 * ran out of memory!
+			 */
+			do_group_exit(SIGKILL);
+			return;
+		}
+		local_irq_disable();
+	}
+
 	clts();				/* Allow maths ops (or we recurse) */
-	if (!tsk_used_math(tsk))
-		init_fpu(tsk);
 	restore_fpu(tsk);
 	thread->status |= TS_USEDFPU;	/* So we fnsave on switch_to() */
 	tsk->fpu_counter++;

arch/x86/kernel/traps_64.c

@@ -1124,10 +1124,23 @@ asmlinkage void __attribute__((weak)) mce_threshold_interrupt(void)
 asmlinkage void math_state_restore(void)
 {
 	struct task_struct *me = current;
-	clts();			/* Allow maths ops (or we recurse) */
 
-	if (!used_math())
-		init_fpu(me);
+	if (!used_math()) {
+		local_irq_enable();
+		/*
+		 * does a slab alloc which can sleep
+		 */
+		if (init_fpu(me)) {
+			/*
+			 * ran out of memory!
+			 */
+			do_group_exit(SIGKILL);
+			return;
+		}
+		local_irq_disable();
+	}
+
+	clts();			/* Allow maths ops (or we recurse) */
 	restore_fpu_checking(&me->thread.xstate->fxsave);
 	task_thread_info(me)->status |= TS_USEDFPU;
 	me->fpu_counter++;

include/asm-x86/i387.h

@@ -21,7 +21,7 @@
 
 extern void fpu_init(void);
 extern void mxcsr_feature_mask_init(void);
-extern void init_fpu(struct task_struct *child);
+extern int init_fpu(struct task_struct *child);
 extern asmlinkage void math_state_restore(void);
 extern void init_thread_xstate(void);
 

include/asm-x86/processor.h

@@ -366,6 +366,8 @@ DECLARE_PER_CPU(struct orig_ist, orig_ist);
 
 extern void print_cpu_info(struct cpuinfo_x86 *);
 extern unsigned int xstate_size;
+extern void free_thread_xstate(struct task_struct *);
+extern struct kmem_cache *task_xstate_cachep;
 extern void init_scattered_cpuid_features(struct cpuinfo_x86 *c);
 extern unsigned int init_intel_cacheinfo(struct cpuinfo_x86 *c);
 extern unsigned short num_cache_leaves;