x86, fpu: split FPU state from task struct - v5

Split the FPU save area from the task struct. This allows easy migration
of FPU context, and it's generally cleaner. It also allows the following
two optimizations:

1) only allocate when the application actually uses FPU, so in the first
lazy FPU trap. This could save memory for non-fpu using apps. Next patch
does this lazy allocation.

2) allocate the right size for the actual cpu rather than 512 bytes always.
Patches enabling xsave/xrstor support (coming shortly) will take advantage
of this.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: 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/Makefile

@@ -29,6 +29,7 @@ obj-$(CONFIG_X86_64)	+= pci-nommu_64.o bugs_64.o
 obj-y			+= tsc_$(BITS).o io_delay.o rtc.o
 
 obj-$(CONFIG_X86_TRAMPOLINE)	+= trampoline.o
+obj-y				+= process.o
 obj-y				+= i387.o
 obj-y				+= ptrace.o
 obj-y				+= ds.o

arch/x86/kernel/i387.c

@@ -8,6 +8,7 @@
 #include <linux/module.h>
 #include <linux/regset.h>
 #include <linux/sched.h>
+#include <linux/bootmem.h>
 
 #include <asm/sigcontext.h>
 #include <asm/processor.h>
@@ -35,24 +36,36 @@
 #endif
 
 static unsigned int		mxcsr_feature_mask __read_mostly = 0xffffffffu;
+unsigned int xstate_size;
+static struct i387_fxsave_struct fx_scratch __cpuinitdata;
 
-void mxcsr_feature_mask_init(void)
+void __cpuinit mxcsr_feature_mask_init(void)
 {
 	unsigned long mask = 0;
 
 	clts();
 	if (cpu_has_fxsr) {
-		memset(&current->thread.i387.fxsave, 0,
-		       sizeof(struct i387_fxsave_struct));
-		asm volatile("fxsave %0" : : "m" (current->thread.i387.fxsave));
-		mask = current->thread.i387.fxsave.mxcsr_mask;
+		memset(&fx_scratch, 0, sizeof(struct i387_fxsave_struct));
+		asm volatile("fxsave %0" : : "m" (fx_scratch));
+		mask = fx_scratch.mxcsr_mask;
 		if (mask == 0)
 			mask = 0x0000ffbf;
 	}
 	mxcsr_feature_mask &= mask;
 	stts();
 }
 
+void __init init_thread_xstate(void)
+{
+	if (cpu_has_fxsr)
+		xstate_size = sizeof(struct i387_fxsave_struct);
+#ifdef CONFIG_X86_32
+	else
+		xstate_size = sizeof(struct i387_fsave_struct);
+#endif
+	init_task.thread.xstate = alloc_bootmem(xstate_size);
+}
+
 #ifdef CONFIG_X86_64
 /*
  * Called at bootup to set up the initial FPU state that is later cloned
@@ -61,10 +74,6 @@ void mxcsr_feature_mask_init(void)
 void __cpuinit fpu_init(void)
 {
 	unsigned long oldcr0 = read_cr0();
-	extern void __bad_fxsave_alignment(void);
-
-	if (offsetof(struct task_struct, thread.i387.fxsave) & 15)
-		__bad_fxsave_alignment();
 
 	set_in_cr4(X86_CR4_OSFXSR);
 	set_in_cr4(X86_CR4_OSXMMEXCPT);
@@ -93,18 +102,19 @@ void init_fpu(struct task_struct *tsk)
 	}
 
 	if (cpu_has_fxsr) {
-		memset(&tsk->thread.i387.fxsave, 0,
-		       sizeof(struct i387_fxsave_struct));
-		tsk->thread.i387.fxsave.cwd = 0x37f;
+		struct i387_fxsave_struct *fx = &tsk->thread.xstate->fxsave;
+
+		memset(fx, 0, xstate_size);
+		fx->cwd = 0x37f;
 		if (cpu_has_xmm)
-			tsk->thread.i387.fxsave.mxcsr = MXCSR_DEFAULT;
+			fx->mxcsr = MXCSR_DEFAULT;
 	} else {
-		memset(&tsk->thread.i387.fsave, 0,
-		       sizeof(struct i387_fsave_struct));
-		tsk->thread.i387.fsave.cwd = 0xffff037fu;
-		tsk->thread.i387.fsave.swd = 0xffff0000u;
-		tsk->thread.i387.fsave.twd = 0xffffffffu;
-		tsk->thread.i387.fsave.fos = 0xffff0000u;
+		struct i387_fsave_struct *fp = &tsk->thread.xstate->fsave;
+		memset(fp, 0, xstate_size);
+		fp->cwd = 0xffff037fu;
+		fp->swd = 0xffff0000u;
+		fp->twd = 0xffffffffu;
+		fp->fos = 0xffff0000u;
 	}
 	/*
 	 * Only the device not available exception or ptrace can call init_fpu.
@@ -132,7 +142,7 @@ int xfpregs_get(struct task_struct *target, const struct user_regset *regset,
 	init_fpu(target);
 
 	return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
-				   &target->thread.i387.fxsave, 0, -1);
+				   &target->thread.xstate->fxsave, 0, -1);
 }
 
 int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
@@ -148,12 +158,12 @@ int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
 	set_stopped_child_used_math(target);
 
 	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
-				 &target->thread.i387.fxsave, 0, -1);
+				 &target->thread.xstate->fxsave, 0, -1);
 
 	/*
 	 * mxcsr reserved bits must be masked to zero for security reasons.
 	 */
-	target->thread.i387.fxsave.mxcsr &= mxcsr_feature_mask;
+	target->thread.xstate->fxsave.mxcsr &= mxcsr_feature_mask;
 
 	return ret;
 }
@@ -233,7 +243,7 @@ static inline u32 twd_fxsr_to_i387(struct i387_fxsave_struct *fxsave)
 static void
 convert_from_fxsr(struct user_i387_ia32_struct *env, struct task_struct *tsk)
 {
-	struct i387_fxsave_struct *fxsave = &tsk->thread.i387.fxsave;
+	struct i387_fxsave_struct *fxsave = &tsk->thread.xstate->fxsave;
 	struct _fpreg *to = (struct _fpreg *) &env->st_space[0];
 	struct _fpxreg *from = (struct _fpxreg *) &fxsave->st_space[0];
 	int i;
@@ -273,7 +283,7 @@ static void convert_to_fxsr(struct task_struct *tsk,
 			    const struct user_i387_ia32_struct *env)
 
 {
-	struct i387_fxsave_struct *fxsave = &tsk->thread.i387.fxsave;
+	struct i387_fxsave_struct *fxsave = &tsk->thread.xstate->fxsave;
 	struct _fpreg *from = (struct _fpreg *) &env->st_space[0];
 	struct _fpxreg *to = (struct _fpxreg *) &fxsave->st_space[0];
 	int i;
@@ -310,7 +320,8 @@ int fpregs_get(struct task_struct *target, const struct user_regset *regset,
 
 	if (!cpu_has_fxsr) {
 		return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
-					   &target->thread.i387.fsave, 0, -1);
+					   &target->thread.xstate->fsave, 0,
+					   -1);
 	}
 
 	if (kbuf && pos == 0 && count == sizeof(env)) {
@@ -338,7 +349,7 @@ int fpregs_set(struct task_struct *target, const struct user_regset *regset,
 
 	if (!cpu_has_fxsr) {
 		return user_regset_copyin(&pos, &count, &kbuf, &ubuf,
-					  &target->thread.i387.fsave, 0, -1);
+					  &target->thread.xstate->fsave, 0, -1);
 	}
 
 	if (pos > 0 || count < sizeof(env))
@@ -358,18 +369,19 @@ int fpregs_set(struct task_struct *target, const struct user_regset *regset,
 static inline int save_i387_fsave(struct _fpstate_ia32 __user *buf)
 {
 	struct task_struct *tsk = current;
+	struct i387_fsave_struct *fp = &tsk->thread.xstate->fsave;
 
 	unlazy_fpu(tsk);
-	tsk->thread.i387.fsave.status = tsk->thread.i387.fsave.swd;
-	if (__copy_to_user(buf, &tsk->thread.i387.fsave,
-			   sizeof(struct i387_fsave_struct)))
+	fp->status = fp->swd;
+	if (__copy_to_user(buf, fp, sizeof(struct i387_fsave_struct)))
 		return -1;
 	return 1;
 }
 
 static int save_i387_fxsave(struct _fpstate_ia32 __user *buf)
 {
 	struct task_struct *tsk = current;
+	struct i387_fxsave_struct *fx = &tsk->thread.xstate->fxsave;
 	struct user_i387_ia32_struct env;
 	int err = 0;
 
@@ -379,12 +391,12 @@ static int save_i387_fxsave(struct _fpstate_ia32 __user *buf)
 	if (__copy_to_user(buf, &env, sizeof(env)))
 		return -1;
 
-	err |= __put_user(tsk->thread.i387.fxsave.swd, &buf->status);
+	err |= __put_user(fx->swd, &buf->status);
 	err |= __put_user(X86_FXSR_MAGIC, &buf->magic);
 	if (err)
 		return -1;
 
-	if (__copy_to_user(&buf->_fxsr_env[0], &tsk->thread.i387.fxsave,
+	if (__copy_to_user(&buf->_fxsr_env[0], fx,
 			   sizeof(struct i387_fxsave_struct)))
 		return -1;
 	return 1;
@@ -417,7 +429,7 @@ static inline int restore_i387_fsave(struct _fpstate_ia32 __user *buf)
 	struct task_struct *tsk = current;
 
 	clear_fpu(tsk);
-	return __copy_from_user(&tsk->thread.i387.fsave, buf,
+	return __copy_from_user(&tsk->thread.xstate->fsave, buf,
 				sizeof(struct i387_fsave_struct));
 }
 
@@ -428,10 +440,10 @@ static int restore_i387_fxsave(struct _fpstate_ia32 __user *buf)
 	int err;
 
 	clear_fpu(tsk);
-	err = __copy_from_user(&tsk->thread.i387.fxsave, &buf->_fxsr_env[0],
+	err = __copy_from_user(&tsk->thread.xstate->fxsave, &buf->_fxsr_env[0],
 			       sizeof(struct i387_fxsave_struct));
 	/* mxcsr reserved bits must be masked to zero for security reasons */
-	tsk->thread.i387.fxsave.mxcsr &= mxcsr_feature_mask;
+	tsk->thread.xstate->fxsave.mxcsr &= mxcsr_feature_mask;
 	if (err || __copy_from_user(&env, buf, sizeof(env)))
 		return 1;
 	convert_to_fxsr(tsk, &env);

arch/x86/kernel/process.c

@@ -0,0 +1,35 @@
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/smp.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+
+static 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 (!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)
+{
+	kmem_cache_free(task_xstate_cachep, ti->task->thread.xstate);
+	ti->task->thread.xstate = NULL;
+
+	free_pages((unsigned long)(ti), get_order(THREAD_SIZE));
+}
+
+void arch_task_cache_init(void)
+{
+        task_xstate_cachep =
+        	kmem_cache_create("task_xstate", xstate_size,
+				  __alignof__(union thread_xstate),
+				  SLAB_PANIC, NULL);
+}

arch/x86/kernel/process_32.c

@@ -703,7 +703,7 @@ struct task_struct * __switch_to(struct task_struct *prev_p, struct task_struct
 
 	/* we're going to use this soon, after a few expensive things */
 	if (next_p->fpu_counter > 5)
-		prefetch(&next->i387.fxsave);
+		prefetch(next->xstate);
 
 	/*
 	 * Reload esp0.

arch/x86/kernel/process_64.c

@@ -682,7 +682,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 
 	/* we're going to use this soon, after a few expensive things */
 	if (next_p->fpu_counter>5)
-		prefetch(&next->i387.fxsave);
+		prefetch(next->xstate);
 
 	/*
 	 * Reload esp0, LDT and the page table pointer:

arch/x86/kernel/traps_32.c

@@ -1208,11 +1208,6 @@ void __init trap_init(void)
 #endif
 	set_trap_gate(19, &simd_coprocessor_error);
 
-	/*
-	 * Verify that the FXSAVE/FXRSTOR data will be 16-byte aligned.
-	 * Generate a build-time error if the alignment is wrong.
-	 */
-	BUILD_BUG_ON(offsetof(struct task_struct, thread.i387.fxsave) & 15);
 	if (cpu_has_fxsr) {
 		printk(KERN_INFO "Enabling fast FPU save and restore... ");
 		set_in_cr4(X86_CR4_OSFXSR);
@@ -1233,6 +1228,7 @@ void __init trap_init(void)
 
 	set_bit(SYSCALL_VECTOR, used_vectors);
 
+	init_thread_xstate();
 	/*
 	 * Should be a barrier for any external CPU state:
 	 */

arch/x86/kernel/traps_64.c

@@ -1128,7 +1128,7 @@ asmlinkage void math_state_restore(void)
 
 	if (!used_math())
 		init_fpu(me);
-	restore_fpu_checking(&me->thread.i387.fxsave);
+	restore_fpu_checking(&me->thread.xstate->fxsave);
 	task_thread_info(me)->status |= TS_USEDFPU;
 	me->fpu_counter++;
 }
@@ -1163,6 +1163,10 @@ void __init trap_init(void)
 	set_system_gate(IA32_SYSCALL_VECTOR, ia32_syscall);
 #endif
 
+	/*
+	 * initialize the per thread extended state:
+	 */
+        init_thread_xstate();
 	/*
 	 * Should be a barrier for any external CPU state.
 	 */

arch/x86/math-emu/fpu_entry.c

@@ -678,7 +678,7 @@ int fpregs_soft_set(struct task_struct *target,
 		    unsigned int pos, unsigned int count,
 		    const void *kbuf, const void __user *ubuf)
 {
-	struct i387_soft_struct *s387 = &target->thread.i387.soft;
+	struct i387_soft_struct *s387 = &target->thread.xstate->soft;
 	void *space = s387->st_space;
 	int ret;
 	int offset, other, i, tags, regnr, tag, newtop;
@@ -730,7 +730,7 @@ int fpregs_soft_get(struct task_struct *target,
 		    unsigned int pos, unsigned int count,
 		    void *kbuf, void __user *ubuf)
 {
-	struct i387_soft_struct *s387 = &target->thread.i387.soft;
+	struct i387_soft_struct *s387 = &target->thread.xstate->soft;
 	const void *space = s387->st_space;
 	int ret;
 	int offset = (S387->ftop & 7) * 10, other = 80 - offset;

arch/x86/math-emu/fpu_system.h

@@ -35,8 +35,8 @@
 #define SEG_EXPAND_DOWN(s)	(((s).b & ((1 << 11) | (1 << 10))) \
 				 == (1 << 10))
 
-#define I387			(current->thread.i387)
-#define FPU_info		(I387.soft.info)
+#define I387			(current->thread.xstate)
+#define FPU_info		(I387->soft.info)
 
 #define FPU_CS			(*(unsigned short *) &(FPU_info->___cs))
 #define FPU_SS			(*(unsigned short *) &(FPU_info->___ss))
@@ -46,25 +46,25 @@
 #define FPU_EIP			(FPU_info->___eip)
 #define FPU_ORIG_EIP		(FPU_info->___orig_eip)
 
-#define FPU_lookahead           (I387.soft.lookahead)
+#define FPU_lookahead           (I387->soft.lookahead)
 
 /* nz if ip_offset and cs_selector are not to be set for the current
    instruction. */
-#define no_ip_update		(*(u_char *)&(I387.soft.no_update))
-#define FPU_rm			(*(u_char *)&(I387.soft.rm))
+#define no_ip_update		(*(u_char *)&(I387->soft.no_update))
+#define FPU_rm			(*(u_char *)&(I387->soft.rm))
 
 /* Number of bytes of data which can be legally accessed by the current
    instruction. This only needs to hold a number <= 108, so a byte will do. */
-#define access_limit		(*(u_char *)&(I387.soft.alimit))
+#define access_limit		(*(u_char *)&(I387->soft.alimit))
 
-#define partial_status		(I387.soft.swd)
-#define control_word		(I387.soft.cwd)
-#define fpu_tag_word		(I387.soft.twd)
-#define registers		(I387.soft.st_space)
-#define top			(I387.soft.ftop)
+#define partial_status		(I387->soft.swd)
+#define control_word		(I387->soft.cwd)
+#define fpu_tag_word		(I387->soft.twd)
+#define registers		(I387->soft.st_space)
+#define top			(I387->soft.ftop)
 
-#define instruction_address	(*(struct address *)&I387.soft.fip)
-#define operand_address		(*(struct address *)&I387.soft.foo)
+#define instruction_address	(*(struct address *)&I387->soft.fip)
+#define operand_address		(*(struct address *)&I387->soft.foo)
 
 #define FPU_access_ok(x,y,z)	if ( !access_ok(x,y,z) ) \
 				math_abort(FPU_info,SIGSEGV)

arch/x86/math-emu/reg_ld_str.c

@@ -1180,8 +1180,8 @@ u_char __user *fstenv(fpu_addr_modes addr_modes, u_char __user *d)
 		control_word |= 0xffff0040;
 		partial_status = status_word() | 0xffff0000;
 		fpu_tag_word |= 0xffff0000;
-		I387.soft.fcs &= ~0xf8000000;
-		I387.soft.fos |= 0xffff0000;
+		I387->soft.fcs &= ~0xf8000000;
+		I387->soft.fos |= 0xffff0000;
 #endif /* PECULIAR_486 */
 		if (__copy_to_user(d, &control_word, 7 * 4))
 			FPU_abort;