powerpc: Prepare for splitting giveup_{fpu, altivec, vsx} in two

This prepares for the decoupling of saving {fpu,altivec,vsx} registers and
marking {fpu,altivec,vsx} as being unused by a thread.

Currently giveup_{fpu,altivec,vsx}() does both however optimisations to
task switching can be made if these two operations are decoupled.
save_all() will permit the saving of registers to thread structs and leave
threads MSR with bits enabled.

This patch introduces no functional change.
Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/reg.h

@@ -75,6 +75,14 @@
 #define MSR_HV		0
 #endif
 
+/*
+ * To be used in shared book E/book S, this avoids needing to worry about
+ * book S/book E in shared code
+ */
+#ifndef MSR_SPE
+#define MSR_SPE 	0
+#endif
+
 #define MSR_VEC		__MASK(MSR_VEC_LG)	/* Enable AltiVec */
 #define MSR_VSX		__MASK(MSR_VSX_LG)	/* Enable VSX */
 #define MSR_POW		__MASK(MSR_POW_LG)	/* Enable Power Management */

arch/powerpc/include/asm/switch_to.h

@@ -34,6 +34,7 @@ static inline void disable_kernel_fp(void)
 	msr_check_and_clear(MSR_FP);
 }
 #else
+static inline void __giveup_fpu(struct task_struct *t) { }
 static inline void flush_fp_to_thread(struct task_struct *t) { }
 #endif
 
@@ -46,6 +47,8 @@ static inline void disable_kernel_altivec(void)
 {
 	msr_check_and_clear(MSR_VEC);
 }
+#else
+static inline void __giveup_altivec(struct task_struct *t) { }
 #endif
 
 #ifdef CONFIG_VSX
@@ -57,6 +60,8 @@ 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
@@ -68,6 +73,8 @@ static inline void disable_kernel_spe(void)
 {
 	msr_check_and_clear(MSR_SPE);
 }
+#else
+static inline void __giveup_spe(struct task_struct *t) { }
 #endif
 
 static inline void clear_task_ebb(struct task_struct *t)

arch/powerpc/kernel/process.c

@@ -444,12 +444,41 @@ void restore_math(struct pt_regs *regs)
 	regs->msr = msr;
 }
 
+void save_all(struct task_struct *tsk)
+{
+	unsigned long usermsr;
+
+	if (!tsk->thread.regs)
+		return;
+
+	usermsr = tsk->thread.regs->msr;
+
+	if ((usermsr & msr_all_available) == 0)
+		return;
+
+	msr_check_and_set(msr_all_available);
+
+	if (usermsr & MSR_FP)
+		__giveup_fpu(tsk);
+
+	if (usermsr & MSR_VEC)
+		__giveup_altivec(tsk);
+
+	if (usermsr & MSR_VSX)
+		__giveup_vsx(tsk);
+
+	if (usermsr & MSR_SPE)
+		__giveup_spe(tsk);
+
+	msr_check_and_clear(msr_all_available);
+}
+
 void flush_all_to_thread(struct task_struct *tsk)
 {
 	if (tsk->thread.regs) {
 		preempt_disable();
 		BUG_ON(tsk != current);
-		giveup_all(tsk);
+		save_all(tsk);
 
 #ifdef CONFIG_SPE
 		if (tsk->thread.regs->msr & MSR_SPE)