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Subject[RFC] riscv: Add jump-label implementation
Date
Add basic jump-label implementation heavily based
on the ARM64 version.

Tested on the HiFive Unleashed.

Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
---

This seems to work on my HiFive Unleashed. At least boots, runs fine
and the static key self-tests doesn't complain, but I'm sure I've missed
something, so I'm sending this as an RFC.

/Emil

.../core/jump-labels/arch-support.txt | 2 +-
arch/riscv/Kconfig | 2 +
arch/riscv/include/asm/jump_label.h | 59 +++++++++++++++++++
arch/riscv/kernel/Makefile | 2 +
arch/riscv/kernel/jump_label.c | 44 ++++++++++++++
5 files changed, 108 insertions(+), 1 deletion(-)
create mode 100644 arch/riscv/include/asm/jump_label.h
create mode 100644 arch/riscv/kernel/jump_label.c

diff --git a/Documentation/features/core/jump-labels/arch-support.txt b/Documentation/features/core/jump-labels/arch-support.txt
index 632a1c7aefa2..760243d18ed7 100644
--- a/Documentation/features/core/jump-labels/arch-support.txt
+++ b/Documentation/features/core/jump-labels/arch-support.txt
@@ -23,7 +23,7 @@
| openrisc: | TODO |
| parisc: | ok |
| powerpc: | ok |
- | riscv: | TODO |
+ | riscv: | ok |
| s390: | ok |
| sh: | TODO |
| sparc: | ok |
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index fd639937e251..d2f5c53fdc19 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -46,6 +46,8 @@ config RISCV
select GENERIC_TIME_VSYSCALL if MMU && 64BIT
select HANDLE_DOMAIN_IRQ
select HAVE_ARCH_AUDITSYSCALL
+ select HAVE_ARCH_JUMP_LABEL
+ select HAVE_ARCH_JUMP_LABEL_RELATIVE
select HAVE_ARCH_KASAN if MMU && 64BIT
select HAVE_ARCH_KGDB
select HAVE_ARCH_KGDB_QXFER_PKT
diff --git a/arch/riscv/include/asm/jump_label.h b/arch/riscv/include/asm/jump_label.h
new file mode 100644
index 000000000000..29be6d351866
--- /dev/null
+++ b/arch/riscv/include/asm/jump_label.h
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 Emil Renner Berthing
+ *
+ * Based on arch/arm64/include/asm/jump_label.h
+ */
+#ifndef __ASM_JUMP_LABEL_H
+#define __ASM_JUMP_LABEL_H
+
+#ifndef __ASSEMBLY__
+
+#include <linux/types.h>
+
+#define JUMP_LABEL_NOP_SIZE 4
+
+static __always_inline bool arch_static_branch(struct static_key *key,
+ bool branch)
+{
+ asm_volatile_goto(
+ " .option push \n\n"
+ " .option norelax \n\n"
+ " .option norvc \n\n"
+ "1: nop \n\t"
+ " .option pop \n\n"
+ " .pushsection __jump_table, \"aw\" \n\t"
+ " .align 3 \n\t"
+ " .long 1b - ., %l[l_yes] - . \n\t"
+ " .quad %0 - . \n\t"
+ " .popsection \n\t"
+ : : "i"(&((char *)key)[branch ? 1 : 0]) : : 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(
+ " .option push \n\n"
+ " .option norelax \n\n"
+ " .option norvc \n\n"
+ "1: jal zero, %l[l_yes] \n\t"
+ " .option pop \n\n"
+ " .pushsection __jump_table, \"aw\" \n\t"
+ " .align 3 \n\t"
+ " .long 1b - ., %l[l_yes] - . \n\t"
+ " .quad %0 - . \n\t"
+ " .popsection \n\t"
+ : : "i"(&((char *)key)[branch ? 1 : 0]) : : l_yes);
+
+ return false;
+l_yes:
+ return true;
+}
+
+#endif /* __ASSEMBLY__ */
+#endif /* __ASM_JUMP_LABEL_H */
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index b355cf485671..a5287ab9f7f2 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -53,4 +53,6 @@ endif
obj-$(CONFIG_HOTPLUG_CPU) += cpu-hotplug.o
obj-$(CONFIG_KGDB) += kgdb.o

+obj-$(CONFIG_JUMP_LABEL) += jump_label.o
+
clean:
diff --git a/arch/riscv/kernel/jump_label.c b/arch/riscv/kernel/jump_label.c
new file mode 100644
index 000000000000..55b2d742efe1
--- /dev/null
+++ b/arch/riscv/kernel/jump_label.c
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2020 Emil Renner Berthing
+ *
+ * Based on arch/arm64/kernel/jump_label.c
+ */
+#include <linux/kernel.h>
+#include <linux/jump_label.h>
+#include <asm/patch.h>
+
+#define RISCV_INSN_NOP 0x00000013
+#define RISCV_INSN_JAL 0x0000006f
+
+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) {
+ u32 offset = jump_entry_target(entry) - jump_entry_code(entry);
+
+ insn = RISCV_INSN_JAL |
+ ((offset & GENMASK(19, 12)) << (12 - 12)) |
+ ((offset & GENMASK(11, 11)) << (20 - 11)) |
+ ((offset & GENMASK(10, 1)) << (21 - 1)) |
+ ((offset & GENMASK(20, 20)) << (31 - 20));
+ } else
+ insn = RISCV_INSN_NOP;
+
+ patch_text_nosync(addr, &insn, sizeof(insn));
+}
+
+void arch_jump_label_transform_static(struct jump_entry *entry,
+ enum jump_label_type type)
+{
+ /*
+ * We use the same instructions in the arch_static_branch and
+ * arch_static_branch_jump inline functions, so there's no
+ * need to patch them up here.
+ * The core will call arch_jump_label_transform when those
+ * instructions need to be replaced.
+ */
+}
--
2.27.0
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