[PATCH] parisc: Add static branch and JUMP_LABEL feature (v2)

[Helge Deller <deller@gmx.de>]

v1: Initial patch
v2: Fixes, correctly encode branch instruction, check distance, check on 32-
    and 64-bit kernel

Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index 26c215570adf..c971256a74d2 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -45,6 +45,8 @@ config PARISC
 	select HAVE_DEBUG_STACKOVERFLOW
 	select HAVE_ARCH_AUDITSYSCALL
 	select HAVE_ARCH_HASH
+	select HAVE_ARCH_JUMP_LABEL
+	select HAVE_ARCH_JUMP_LABEL_RELATIVE
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_REGS_AND_STACK_ACCESS_API
diff --git a/arch/parisc/include/asm/jump_label.h b/arch/parisc/include/asm/jump_label.h
new file mode 100644
index 000000000000..7efb1aa2f7f8
--- /dev/null
+++ b/arch/parisc/include/asm/jump_label.h
@@ -0,0 +1,43 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_PARISC_JUMP_LABEL_H
+#define _ASM_PARISC_JUMP_LABEL_H
+
+#ifndef __ASSEMBLY__
+
+#include <linux/types.h>
+#include <asm/assembly.h>
+
+#define JUMP_LABEL_NOP_SIZE 4
+
+static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
+{
+	asm_volatile_goto("1:\n\t"
+		 "nop\n\t"
+		 ".pushsection __jump_table,  \"aw\"\n\t"
+		 ".word 1b - ., %l[l_yes] - .\n\t"
+		 __stringify(ASM_ULONG_INSN) " %c0 - .\n\t"
+		 ".popsection\n\t"
+		 : :  "i" (&((char *)key)[branch]) :  : l_yes);
+
+	return false;
+l_yes:
+	return true;
+}
+
+static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
+{
+	asm_volatile_goto("1:\n\t"
+		 "b,n %l[l_yes]\n\t"
+		 ".pushsection __jump_table,  \"aw\"\n\t"
+		 ".word 1b - ., %l[l_yes] - .\n\t"
+		 __stringify(ASM_ULONG_INSN) " %c0 - .\n\t"
+		 ".popsection\n\t"
+		 : :  "i" (&((char *)key)[branch]) :  : l_yes);
+
+	return false;
+l_yes:
+	return true;
+}
+
+#endif  /* __ASSEMBLY__ */
+#endif
diff --git a/arch/parisc/kernel/Makefile b/arch/parisc/kernel/Makefile
index b818b28c8a99..fc0df5c44468 100644
--- a/arch/parisc/kernel/Makefile
+++ b/arch/parisc/kernel/Makefile
@@ -33,5 +33,6 @@ obj-$(CONFIG_64BIT)	+= perf.o perf_asm.o $(obj64-y)
 obj-$(CONFIG_PARISC_CPU_TOPOLOGY)	+= topology.o
 obj-$(CONFIG_FUNCTION_TRACER)		+= ftrace.o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER)	+= ftrace.o
+obj-$(CONFIG_JUMP_LABEL)		+= jump_label.o
 obj-$(CONFIG_KGDB)			+= kgdb.o
 obj-$(CONFIG_KPROBES)			+= kprobes.o
diff --git a/arch/parisc/kernel/jump_label.c b/arch/parisc/kernel/jump_label.c
new file mode 100644
index 000000000000..d2f3cb12e282
--- /dev/null
+++ b/arch/parisc/kernel/jump_label.c
@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2019 Helge Deller <deller@gmx.de>
+ *
+ * Based on arch/arm64/kernel/jump_label.c
+ */
+#include <linux/kernel.h>
+#include <linux/jump_label.h>
+#include <linux/bug.h>
+#include <asm/alternative.h>
+#include <asm/patch.h>
+
+static inline int reassemble_17(int as17)
+{
+	return (((as17 & 0x10000) >> 16) |
+		((as17 & 0x0f800) << 5) |
+		((as17 & 0x00400) >> 8) |
+		((as17 & 0x003ff) << 3));
+}
+
+void arch_jump_label_transform(struct jump_entry *entry,
+			       enum jump_label_type type)
+{
+	void *addr = (void *)jump_entry_code(entry);
+	u32 insn;
+
+	if (type == JUMP_LABEL_JMP) {
+		void *target = (void *)jump_entry_target(entry);
+		int distance = target - addr;
+		/*
+		 * Encode the PA1.1 "b,n" instruction with a 17-bit
+		 * displacement.  In case we hit the BUG(), we could use
+		 * another branch instruction with a 22-bit displacement on
+		 * 64-bit CPUs instead. But this seems sufficient for now.
+		 */
+		distance -= 8;
+		BUG_ON(distance > 262143 || distance < -262144);
+		insn = 0xe8000002 | reassemble_17(distance >> 2);
+	} else {
+		insn = INSN_NOP;
+	}
+
+	patch_text(addr, insn);
+}
+
+void arch_jump_label_transform_static(struct jump_entry *entry,
+				      enum jump_label_type type)
+{
+	/*
+	 * We use the architected NOP in arch_static_branch, so there's no
+	 * need to patch an identical NOP over the top of it here. The core
+	 * will call arch_jump_label_transform from a module notifier if the
+	 * NOP needs to be replaced by a branch.
+	 */
+}
diff --git a/arch/parisc/kernel/vmlinux.lds.S b/arch/parisc/kernel/vmlinux.lds.S
index c3b1b9c24ede..a8be7a47fcc0 100644
--- a/arch/parisc/kernel/vmlinux.lds.S
+++ b/arch/parisc/kernel/vmlinux.lds.S
@@ -18,6 +18,9 @@
 				*(.data..vm0.pgd) \
 				*(.data..vm0.pte)

+/* No __ro_after_init data in the .rodata section - which will always be ro */
+#define RO_AFTER_INIT_DATA
+
 #include <asm-generic/vmlinux.lds.h>

 /* needed for the processor specific cache alignment size */