x86/fpu: Rename fpu__unlazy_stopped() to fpu__activate_stopped()

In line with the fpstate_activate() change, name
fpu__unlazy_stopped() in a similar fashion as well: its purpose
is to make the fpstate of a stopped task the current and active FPU
context, which may require unlazying and initialization.

The unlazying is just part of the job, the main concept is to make
the fpstate active.

Also clarify the function's description to clarify its exact
usage and the background behind it all.
Reviewed-by: NBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

arch/x86/kernel/fpu/core.c

@@ -276,29 +276,30 @@ void fpu__activate_curr(struct fpu *fpu)
 EXPORT_SYMBOL_GPL(fpu__activate_curr);
 
 /*
- * This function is called before we modify a stopped child's
- * FPU state context.
+ * This function must be called before we modify a stopped child's
+ * fpstate.
  *
  * If the child has not used the FPU before then initialize its
- * FPU context.
+ * fpstate.
  *
  * If the child has used the FPU before then unlazy it.
  *
- * [ After this function call, after the context is modified and
- *   the child task is woken up, the child task will restore
- *   the modified FPU state from the modified context. If we
+ * [ After this function call, after registers in the fpstate are
+ *   modified and the child task has woken up, the child task will
+ *   restore the modified FPU state from the modified context. If we
  *   didn't clear its lazy status here then the lazy in-registers
- *   state pending on its former CPU could be restored, losing
+ *   state pending on its former CPU could be restored, corrupting
  *   the modifications. ]
  *
  * This function is also called before we read a stopped child's
- * FPU state - to make sure it's modified.
+ * FPU state - to make sure it's initialized if the child has
+ * no active FPU state.
  *
  * TODO: A future optimization would be to skip the unlazying in
  *       the read-only case, it's not strictly necessary for
  *       read-only access to the context.
  */
-static void fpu__unlazy_stopped(struct fpu *child_fpu)
+static void fpu__activate_stopped(struct fpu *child_fpu)
 {
 	WARN_ON_ONCE(child_fpu == &current->thread.fpu);
 
@@ -388,7 +389,7 @@ int xfpregs_get(struct task_struct *target, const struct user_regset *regset,
 	if (!cpu_has_fxsr)
 		return -ENODEV;
 
-	fpu__unlazy_stopped(fpu);
+	fpu__activate_stopped(fpu);
 	sanitize_i387_state(target);
 
 	return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
@@ -405,7 +406,7 @@ int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
 	if (!cpu_has_fxsr)
 		return -ENODEV;
 
-	fpu__unlazy_stopped(fpu);
+	fpu__activate_stopped(fpu);
 	sanitize_i387_state(target);
 
 	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
@@ -437,7 +438,7 @@ int xstateregs_get(struct task_struct *target, const struct user_regset *regset,
 	if (!cpu_has_xsave)
 		return -ENODEV;
 
-	fpu__unlazy_stopped(fpu);
+	fpu__activate_stopped(fpu);
 
 	xsave = &fpu->state.xsave;
 
@@ -466,7 +467,7 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
 	if (!cpu_has_xsave)
 		return -ENODEV;
 
-	fpu__unlazy_stopped(fpu);
+	fpu__activate_stopped(fpu);
 
 	xsave = &fpu->state.xsave;
 
@@ -628,7 +629,7 @@ int fpregs_get(struct task_struct *target, const struct user_regset *regset,
 	struct fpu *fpu = &target->thread.fpu;
 	struct user_i387_ia32_struct env;
 
-	fpu__unlazy_stopped(fpu);
+	fpu__activate_stopped(fpu);
 
 	if (!static_cpu_has(X86_FEATURE_FPU))
 		return fpregs_soft_get(target, regset, pos, count, kbuf, ubuf);
@@ -658,7 +659,7 @@ int fpregs_set(struct task_struct *target, const struct user_regset *regset,
 	struct user_i387_ia32_struct env;
 	int ret;
 
-	fpu__unlazy_stopped(fpu);
+	fpu__activate_stopped(fpu);
 
 	sanitize_i387_state(target);