---

yaml
---
r: 287651
b: refs/heads/master
c: 15d8791
h: refs/heads/master
i:
  287649: 390cdfc
  287647: aa22db5
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: c38e23456278e967f094b08247ffc3711b1029b2
+refs/heads/master: 15d8791cae75dca27bfda8ecfe87dca9379d6bb0

trunk/arch/x86/include/asm/i387.h

@@ -399,6 +399,48 @@ static inline void irq_ts_restore(int TS_state)
 		stts();
 }
 
+/*
+ * The question "does this thread have fpu access?"
+ * is slightly racy, since preemption could come in
+ * and revoke it immediately after the test.
+ *
+ * However, even in that very unlikely scenario,
+ * we can just assume we have FPU access - typically
+ * to save the FP state - we'll just take a #NM
+ * fault and get the FPU access back.
+ *
+ * The actual user_fpu_begin/end() functions
+ * need to be preemption-safe, though.
+ *
+ * NOTE! user_fpu_end() must be used only after you
+ * have saved the FP state, and user_fpu_begin() must
+ * be used only immediately before restoring it.
+ * These functions do not do any save/restore on
+ * their own.
+ */
+static inline int user_has_fpu(void)
+{
+	return current_thread_info()->status & TS_USEDFPU;
+}
+
+static inline void user_fpu_end(void)
+{
+	preempt_disable();
+	current_thread_info()->status &= ~TS_USEDFPU;
+	stts();
+	preempt_enable();
+}
+
+static inline void user_fpu_begin(void)
+{
+	preempt_disable();
+	if (!user_has_fpu()) {
+		clts();
+		current_thread_info()->status |= TS_USEDFPU;
+	}
+	preempt_enable();
+}
+
 /*
  * These disable preemption on their own and are safe
  */

trunk/arch/x86/kernel/traps.c

@@ -631,7 +631,6 @@ EXPORT_SYMBOL_GPL(math_state_restore);
 dotraplinkage void __kprobes
 do_device_not_available(struct pt_regs *regs, long error_code)
 {
-	WARN_ON_ONCE(!user_mode_vm(regs));
 #ifdef CONFIG_MATH_EMULATION
 	if (read_cr0() & X86_CR0_EM) {
 		struct math_emu_info info = { };

trunk/arch/x86/kernel/xsave.c

@@ -168,16 +168,15 @@ int save_i387_xstate(void __user *buf)
 	if (!used_math())
 		return 0;
 
-	if (task_thread_info(tsk)->status & TS_USEDFPU) {
+	if (user_has_fpu()) {
 		if (use_xsave())
 			err = xsave_user(buf);
 		else
 			err = fxsave_user(buf);
 
 		if (err)
 			return err;
-		task_thread_info(tsk)->status &= ~TS_USEDFPU;
-		stts();
+		user_fpu_end();
 	} else {
 		sanitize_i387_state(tsk);
 		if (__copy_to_user(buf, &tsk->thread.fpu.state->fxsave,
@@ -292,10 +291,7 @@ int restore_i387_xstate(void __user *buf)
 			return err;
 	}
 
-	if (!(task_thread_info(current)->status & TS_USEDFPU)) {
-		clts();
-		task_thread_info(current)->status |= TS_USEDFPU;
-	}
+	user_fpu_begin();
 	if (use_xsave())
 		err = restore_user_xstate(buf);
 	else