jump label: Add s390 support

Implement the architecture backend for jump label support on s390.

For a shared kernel booted from a NSS silently disable jump labels
because the NSS is read-only. Therefore jump labels will be disabled
in a shared kernel and can't be activated.

Signed-off-by: Jan Glauber <jang@linux.vnet.ibm.com>
LKML-Reference: <6935d2c41ce111e1719176ed4bbd3dbe4de80855.1300299760.git.jbaron@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

4 files changed, 98 insertions, 1 deletions

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 2508a6f31588..4a7f14079e03 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -88,6 +88,7 @@ config S390
         select HAVE_KERNEL_XZ
         select HAVE_GET_USER_PAGES_FAST
         select HAVE_ARCH_MUTEX_CPU_RELAX
+        select HAVE_ARCH_JUMP_LABEL if !MARCH_G5
         select ARCH_INLINE_SPIN_TRYLOCK
         select ARCH_INLINE_SPIN_TRYLOCK_BH
         select ARCH_INLINE_SPIN_LOCK
diff --git a/arch/s390/include/asm/jump_label.h b/arch/s390/include/asm/jump_label.h
new file mode 100644
index 000000000000..95a6cf2b5b67
--- /dev/null
+++ b/arch/s390/include/asm/jump_label.h
@@ -0,0 +1,37 @@
+#ifndef _ASM_S390_JUMP_LABEL_H
+#define _ASM_S390_JUMP_LABEL_H
+
+#include <linux/types.h>
+
+#define JUMP_LABEL_NOP_SIZE 6
+
+#ifdef CONFIG_64BIT
+#define ASM_PTR ".quad"
+#define ASM_ALIGN ".balign 8"
+#else
+#define ASM_PTR ".long"
+#define ASM_ALIGN ".balign 4"
+#endif
+
+static __always_inline bool arch_static_branch(struct jump_label_key *key)
+{
+        asm goto("0:    brcl 0,0\n"
+                ".pushsection __jump_table, \"aw\"\n"
+                ASM_ALIGN "\n"
+                ASM_PTR " 0b, %l[label], %0\n"
+                ".popsection\n"
+                : : "X" (key) : : label);
+        return false;
+label:
+        return true;
+}
+
+typedef unsigned long jump_label_t;
+
+struct jump_entry {
+        jump_label_t code;
+        jump_label_t target;
+        jump_label_t key;
+};
+
+#endif
diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
index 64230bc392fa..5ff15dacb571 100644
--- a/arch/s390/kernel/Makefile
+++ b/arch/s390/kernel/Makefile
@@ -23,7 +23,7 @@ CFLAGS_sysinfo.o += -Iinclude/math-emu -Iarch/s390/math-emu -w
 obj-y   :=  bitmap.o traps.o time.o process.o base.o early.o setup.o \
             processor.o sys_s390.o ptrace.o signal.o cpcmd.o ebcdic.o \
             s390_ext.o debug.o irq.o ipl.o dis.o diag.o mem_detect.o \
-            vdso.o vtime.o sysinfo.o nmi.o sclp.o
+            vdso.o vtime.o sysinfo.o nmi.o sclp.o jump_label.o
 
 obj-y   += $(if $(CONFIG_64BIT),entry64.o,entry.o)
 obj-y   += $(if $(CONFIG_64BIT),reipl64.o,reipl.o)
diff --git a/arch/s390/kernel/jump_label.c b/arch/s390/kernel/jump_label.c
new file mode 100644
index 000000000000..44cc06bedf77
--- /dev/null
+++ b/arch/s390/kernel/jump_label.c
@@ -0,0 +1,59 @@
+/*
+ * Jump label s390 support
+ *
+ * Copyright IBM Corp. 2011
+ * Author(s): Jan Glauber <jang@linux.vnet.ibm.com>
+ */
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/stop_machine.h>
+#include <linux/jump_label.h>
+#include <asm/ipl.h>
+
+#ifdef HAVE_JUMP_LABEL
+
+struct insn {
+        u16 opcode;
+        s32 offset;
+} __packed;
+
+struct insn_args {
+        unsigned long *target;
+        struct insn *insn;
+        ssize_t size;
+};
+
+static int __arch_jump_label_transform(void *data)
+{
+        struct insn_args *args = data;
+        int rc;
+
+        rc = probe_kernel_write(args->target, args->insn, args->size);
+        WARN_ON_ONCE(rc < 0);
+        return 0;
+}
+
+void arch_jump_label_transform(struct jump_entry *entry,
+                               enum jump_label_type type)
+{
+        struct insn_args args;
+        struct insn insn;
+
+        if (type == JUMP_LABEL_ENABLE) {
+                /* brcl 15,offset */
+                insn.opcode = 0xc0f4;
+                insn.offset = (entry->target - entry->code) >> 1;
+        } else {
+                /* brcl 0,0 */
+                insn.opcode = 0xc004;
+                insn.offset = 0;
+        }
+
+        args.target = (void *) entry->code;
+        args.insn = &insn;
+        args.size = JUMP_LABEL_NOP_SIZE;
+
+        stop_machine(__arch_jump_label_transform, &args, NULL);
+}
+
+#endif