powerpc: Inline setup_kup()

setup_kup() is used by both 64-bit and 32-bit code. However on 64-bit
it must not be __init, because it's used for CPU hotplug, whereas on
32-bit it should be __init because it calls setup_kuap/kuep() which
are __init.

We worked around that problem in the past by marking it __ref, see
commit 67d53f3 ("powerpc/mm: fix section mismatch for
setup_kup()").

Marking it __ref basically just omits it from section mismatch
checking, which can lead to bugs, and in fact it did, see commit
44b4c44 ("powerpc/64s: Mark the kuap/kuep functions non __init")

We can avoid all these problems by just making it static inline.
Because all it does is call other functions, making it inline actually
shrinks the 32-bit vmlinux by ~76 bytes.

Make it __always_inline as pointed out by Christophe.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201214123011.311024-1-mpe@ellerman.id.au

arch/powerpc/include/asm/kup.h

@@ -49,8 +49,6 @@ extern bool disable_kuap;
 
 #include <linux/pgtable.h>
 
-void setup_kup(void);
-
 #ifdef CONFIG_PPC_KUEP
 void setup_kuep(bool disabled);
 #else
@@ -85,6 +83,12 @@ static inline void restore_user_access(unsigned long flags) { }
 #endif /* CONFIG_PPC_BOOK3S_64 */
 #endif /* CONFIG_PPC_KUAP */
 
+static __always_inline void setup_kup(void)
+{
+	setup_kuep(disable_kuep);
+	setup_kuap(disable_kuap);
+}
+
 static inline void allow_read_from_user(const void __user *from, unsigned long size)
 {
 	allow_user_access(NULL, from, size, KUAP_READ);

arch/powerpc/mm/init-common.c

@@ -47,12 +47,6 @@ static int __init parse_nosmap(char *p)
 }
 early_param("nosmap", parse_nosmap);
 
-void __ref setup_kup(void)
-{
-	setup_kuep(disable_kuep);
-	setup_kuap(disable_kuap);
-}
-
 #define CTOR(shift) static void ctor_##shift(void *addr) \
 {							\
 	memset(addr, 0, sizeof(void *) << (shift));	\