Merge branch 'x86-fpu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fpu updates from Ingo Molnar:
 "Initial round of kernel_fpu_begin/end cleanups from Oleg Nesterov,
  plus a cleanup from Borislav Petkov"

* 'x86-fpu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86, fpu: Fix math_state_restore() race with kernel_fpu_begin()
  x86, fpu: Don't abuse has_fpu in __kernel_fpu_begin/end()
  x86, fpu: Introduce per-cpu in_kernel_fpu state
  x86/fpu: Use a symbolic name for asm operand

2 files changed, 31 insertions, 20 deletions

diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index a9a4229f6161..81049ffab2d6 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -19,6 +19,19 @@
 #include <asm/fpu-internal.h>
 #include <asm/user.h>
 
+static DEFINE_PER_CPU(bool, in_kernel_fpu);
+
+void kernel_fpu_disable(void)
+{
+        WARN_ON(this_cpu_read(in_kernel_fpu));
+        this_cpu_write(in_kernel_fpu, true);
+}
+
+void kernel_fpu_enable(void)
+{
+        this_cpu_write(in_kernel_fpu, false);
+}
+
 /*
  * Were we in an interrupt that interrupted kernel mode?
  *
@@ -33,6 +46,9 @@
  */
 static inline bool interrupted_kernel_fpu_idle(void)
 {
+        if (this_cpu_read(in_kernel_fpu))
+                return false;
+
         if (use_eager_fpu())
                 return __thread_has_fpu(current);
 
@@ -73,10 +89,10 @@ void __kernel_fpu_begin(void)
 {
         struct task_struct *me = current;
 
+        this_cpu_write(in_kernel_fpu, true);
+
         if (__thread_has_fpu(me)) {
-                __thread_clear_has_fpu(me);
                 __save_init_fpu(me);
-                /* We do 'stts()' in __kernel_fpu_end() */
         } else if (!use_eager_fpu()) {
                 this_cpu_write(fpu_owner_task, NULL);
                 clts();
@@ -86,19 +102,16 @@ EXPORT_SYMBOL(__kernel_fpu_begin);
 
 void __kernel_fpu_end(void)
 {
-        if (use_eager_fpu()) {
-                /*
-                 * For eager fpu, most the time, tsk_used_math() is true.
-                 * Restore the user math as we are done with the kernel usage.
-                 * At few instances during thread exit, signal handling etc,
-                 * tsk_used_math() is false. Those few places will take proper
-                 * actions, so we don't need to restore the math here.
-                 */
-                if (likely(tsk_used_math(current)))
-                        math_state_restore();
-        } else {
+        struct task_struct *me = current;
+
+        if (__thread_has_fpu(me)) {
+                if (WARN_ON(restore_fpu_checking(me)))
+                        drop_init_fpu(me);
+        } else if (!use_eager_fpu()) {
                 stts();
         }
+
+        this_cpu_write(in_kernel_fpu, false);
 }
 EXPORT_SYMBOL(__kernel_fpu_end);
 
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index c74f2f5652da..9d2073e2ecc9 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -859,18 +859,16 @@ void math_state_restore(void)
                 local_irq_disable();
         }
 
+        /* Avoid __kernel_fpu_begin() right after __thread_fpu_begin() */
+        kernel_fpu_disable();
         __thread_fpu_begin(tsk);
-
-        /*
-         * Paranoid restore. send a SIGSEGV if we fail to restore the state.
-         */
         if (unlikely(restore_fpu_checking(tsk))) {
                 drop_init_fpu(tsk);
                 force_sig_info(SIGSEGV, SEND_SIG_PRIV, tsk);
-                return;
+        } else {
+                tsk->thread.fpu_counter++;
         }
-
-        tsk->thread.fpu_counter++;
+        kernel_fpu_enable();
 }
 EXPORT_SYMBOL_GPL(math_state_restore);