powerpc: Add the ability to save VSX without giving it up

This patch adds the ability to be able to save the VSX registers to the
thread struct without giving up (disabling the facility) next time the
process returns to userspace.

This patch builds on a previous optimisation for the FPU and VEC registers
in the thread copy path to avoid a possibly pointless reload of VSX state.
Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/switch_to.h

@@ -56,14 +56,10 @@ static inline void __giveup_altivec(struct task_struct *t) { }
 #ifdef CONFIG_VSX
 extern void enable_kernel_vsx(void);
 extern void flush_vsx_to_thread(struct task_struct *);
-extern void giveup_vsx(struct task_struct *);
-extern void __giveup_vsx(struct task_struct *);
 static inline void disable_kernel_vsx(void)
 {
 	msr_check_and_clear(MSR_FP|MSR_VEC|MSR_VSX);
 }
-#else
-static inline void __giveup_vsx(struct task_struct *t) { }
 #endif
 
 #ifdef CONFIG_SPE

arch/powerpc/kernel/ppc_ksyms.c

@@ -28,10 +28,6 @@ EXPORT_SYMBOL(load_vr_state);
 EXPORT_SYMBOL(store_vr_state);
 #endif
 
-#ifdef CONFIG_VSX
-EXPORT_SYMBOL_GPL(__giveup_vsx);
-#endif
-
 #ifdef CONFIG_EPAPR_PARAVIRT
 EXPORT_SYMBOL(epapr_hypercall_start);
 #endif

arch/powerpc/kernel/process.c

@@ -280,19 +280,31 @@ static inline int restore_altivec(struct task_struct *tsk) { return 0; }
 #endif /* CONFIG_ALTIVEC */
 
 #ifdef CONFIG_VSX
-void giveup_vsx(struct task_struct *tsk)
+static void __giveup_vsx(struct task_struct *tsk)
 {
-	check_if_tm_restore_required(tsk);
-
-	msr_check_and_set(MSR_FP|MSR_VEC|MSR_VSX);
 	if (tsk->thread.regs->msr & MSR_FP)
 		__giveup_fpu(tsk);
 	if (tsk->thread.regs->msr & MSR_VEC)
 		__giveup_altivec(tsk);
+	tsk->thread.regs->msr &= ~MSR_VSX;
+}
+
+static void giveup_vsx(struct task_struct *tsk)
+{
+	check_if_tm_restore_required(tsk);
+
+	msr_check_and_set(MSR_FP|MSR_VEC|MSR_VSX);
 	__giveup_vsx(tsk);
 	msr_check_and_clear(MSR_FP|MSR_VEC|MSR_VSX);
 }
-EXPORT_SYMBOL(giveup_vsx);
+
+static void save_vsx(struct task_struct *tsk)
+{
+	if (tsk->thread.regs->msr & MSR_FP)
+		save_fpu(tsk);
+	if (tsk->thread.regs->msr & MSR_VEC)
+		save_altivec(tsk);
+}
 
 void enable_kernel_vsx(void)
 {
@@ -335,6 +347,7 @@ static int restore_vsx(struct task_struct *tsk)
 }
 #else
 static inline int restore_vsx(struct task_struct *tsk) { return 0; }
+static inline void save_vsx(struct task_struct *tsk) { }
 #endif /* CONFIG_VSX */
 
 #ifdef CONFIG_SPE
@@ -478,14 +491,19 @@ void save_all(struct task_struct *tsk)
 
 	msr_check_and_set(msr_all_available);
 
+	/*
+	 * Saving the way the register space is in hardware, save_vsx boils
+	 * down to a save_fpu() and save_altivec()
+	 */
+	if (usermsr & MSR_VSX) {
+		save_vsx(tsk);
+	} else {
 		if (usermsr & MSR_FP)
 			save_fpu(tsk);
 
 		if (usermsr & MSR_VEC)
 			save_altivec(tsk);
-
-	if (usermsr & MSR_VSX)
-		__giveup_vsx(tsk);
+	}
 
 	if (usermsr & MSR_SPE)
 		__giveup_spe(tsk);

arch/powerpc/kernel/vector.S

@@ -151,23 +151,6 @@ _GLOBAL(load_up_vsx)
 	std	r12,_MSR(r1)
 	b	fast_exception_return
 
-/*
- * __giveup_vsx(tsk)
- * Disable VSX for the task given as the argument.
- * Does NOT save vsx registers.
- */
-_GLOBAL(__giveup_vsx)
-	addi	r3,r3,THREAD		/* want THREAD of task */
-	ld	r5,PT_REGS(r3)
-	cmpdi	0,r5,0
-	beq	1f
-	ld	r4,_MSR-STACK_FRAME_OVERHEAD(r5)
-	lis	r3,MSR_VSX@h
-	andc	r4,r4,r3		/* disable VSX for previous task */
-	std	r4,_MSR-STACK_FRAME_OVERHEAD(r5)
-1:
-	blr
-
 #endif /* CONFIG_VSX */