x86/fpu: Simplify fpu->fpregs_active use

The fpregs_active() inline function is pretty pointless - in almost
all the callsites it can be replaced with a direct fpu->fpregs_active
access.

Do so and eliminate the extra layer of obfuscation.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/20170923130016.21448-16-mingo@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/fpu/internal.h

@@ -542,21 +542,6 @@ static inline void fpregs_activate(struct fpu *fpu)
 	trace_x86_fpu_regs_activated(fpu);
 }
 
-/*
- * 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.
- */
-static inline int fpregs_active(void)
-{
-	return current->thread.fpu.fpregs_active;
-}
-
 /*
  * FPU state switching for scheduling.
  *
@@ -617,7 +602,7 @@ static inline void user_fpu_begin(void)
 	struct fpu *fpu = &current->thread.fpu;
 
 	preempt_disable();
-	if (!fpregs_active())
+	if (!fpu->fpregs_active)
 		fpregs_activate(fpu);
 	preempt_enable();
 }

arch/x86/kernel/fpu/core.c

@@ -367,7 +367,7 @@ void fpu__current_fpstate_write_end(void)
 	 * registers may still be out of date.  Update them with
 	 * an XRSTOR if they are active.
 	 */
-	if (fpregs_active())
+	if (fpu->fpregs_active)
 		copy_kernel_to_fpregs(&fpu->state);
 
 	/*

arch/x86/kernel/fpu/signal.c

@@ -155,7 +155,8 @@ static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf)
  */
 int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
 {
-	struct xregs_state *xsave = &current->thread.fpu.state.xsave;
+	struct fpu *fpu = &current->thread.fpu;
+	struct xregs_state *xsave = &fpu->state.xsave;
 	struct task_struct *tsk = current;
 	int ia32_fxstate = (buf != buf_fx);
 
@@ -170,13 +171,13 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
 			sizeof(struct user_i387_ia32_struct), NULL,
 			(struct _fpstate_32 __user *) buf) ? -1 : 1;
 
-	if (fpregs_active() || using_compacted_format()) {
+	if (fpu->fpregs_active || using_compacted_format()) {
 		/* Save the live register state to the user directly. */
 		if (copy_fpregs_to_sigframe(buf_fx))
 			return -1;
 		/* Update the thread's fxstate to save the fsave header. */
 		if (ia32_fxstate)
-			copy_fxregs_to_kernel(&tsk->thread.fpu);
+			copy_fxregs_to_kernel(fpu);
 	} else {
 		/*
 		 * It is a *bug* if kernel uses compacted-format for xsave
@@ -189,7 +190,7 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
 			return -1;
 		}
 
-		fpstate_sanitize_xstate(&tsk->thread.fpu);
+		fpstate_sanitize_xstate(fpu);
 		if (__copy_to_user(buf_fx, xsave, fpu_user_xstate_size))
 			return -1;
 	}

arch/x86/mm/pkeys.c

@@ -45,7 +45,7 @@ int __execute_only_pkey(struct mm_struct *mm)
 	 */
 	preempt_disable();
 	if (!need_to_set_mm_pkey &&
-	    fpregs_active() &&
+	    current->thread.fpu.fpregs_active &&
 	    !__pkru_allows_read(read_pkru(), execute_only_pkey)) {
 		preempt_enable();
 		return execute_only_pkey;