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>

7 files changed, 90 insertions, 42 deletions

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index c3920ea8ac5..7a2a2e93e84 100644
--- a/arch/x86/kernel/Makefile
+++ b/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
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index 8f8102d967b..baf632b221d 100644
--- a/arch/x86/kernel/i387.c
+++ b/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>
@@ -35,17 +36,18 @@
 #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;
         }
@@ -53,6 +55,17 @@ void mxcsr_feature_mask_init(void)
         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))
@@ -358,11 +369,11 @@ 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;
 }
@@ -370,6 +381,7 @@ static inline int save_i387_fsave(struct _fpstate_ia32 __user *buf)
 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);
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
new file mode 100644
index 00000000000..ead24efbcba
--- /dev/null
+++ b/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);
+}
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index a3790a3f8a8..3890a5dd25f 100644
--- a/arch/x86/kernel/process_32.c
+++ b/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.
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 4c13b1406c7..b795e831afd 100644
--- a/arch/x86/kernel/process_64.c
+++ b/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:
diff --git a/arch/x86/kernel/traps_32.c b/arch/x86/kernel/traps_32.c
index dc4273010f2..8d136a73ce8 100644
--- a/arch/x86/kernel/traps_32.c
+++ b/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:
          */
diff --git a/arch/x86/kernel/traps_64.c b/arch/x86/kernel/traps_64.c
index 6d883b13ef4..dc0cb497eec 100644
--- a/arch/x86/kernel/traps_64.c
+++ b/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++;
 }
@@ -1164,6 +1164,10 @@ void __init trap_init(void)
 #endif
        
         /*
+         * initialize the per thread extended state:
+         */
+        init_thread_xstate();
+        /*
          * Should be a barrier for any external CPU state.
          */
         cpu_init();