powerpc/8xx: Create C version of kuap save/restore/check helpers

In preparation of porting PPC32 to C syscall entry/exit,
create C version of kuap_save_and_lock() and kuap_user_restore() and
kuap_kernel_restore() and kuap_assert_locked() and
kuap_get_and_assert_locked() on 8xx.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/156a7c4b669d26785391422a5581a1d919544c9a.1615552867.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/nohash/32/kup-8xx.h

@@ -34,6 +34,37 @@
 
 #include <asm/reg.h>
 
+static inline void kuap_save_and_lock(struct pt_regs *regs)
+{
+	regs->kuap = mfspr(SPRN_MD_AP);
+	mtspr(SPRN_MD_AP, MD_APG_KUAP);
+}
+
+static inline void kuap_user_restore(struct pt_regs *regs)
+{
+}
+
+static inline void kuap_kernel_restore(struct pt_regs *regs, unsigned long kuap)
+{
+	mtspr(SPRN_MD_AP, regs->kuap);
+}
+
+static inline unsigned long kuap_get_and_assert_locked(void)
+{
+	unsigned long kuap = mfspr(SPRN_MD_AP);
+
+	if (IS_ENABLED(CONFIG_PPC_KUAP_DEBUG))
+		WARN_ON_ONCE(kuap >> 16 != MD_APG_KUAP >> 16);
+
+	return kuap;
+}
+
+static inline void kuap_assert_locked(void)
+{
+	if (IS_ENABLED(CONFIG_PPC_KUAP_DEBUG))
+		kuap_get_and_assert_locked();
+}
+
 static inline void allow_user_access(void __user *to, const void __user *from,
 				     unsigned long size, unsigned long dir)
 {