arm64: add alternative runtime patching

With a blatant copy of some x86 bits we introduce the alternative
runtime patching "framework" to arm64.
This is quite basic for now and we only provide the functions we need
at this time.
This is connected to the newly introduced feature bits.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 64 insertions, 0 deletions

diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c
new file mode 100644
index 000000000000..1a3badab800a
--- /dev/null
+++ b/arch/arm64/kernel/alternative.c
@@ -0,0 +1,64 @@
+/*
+ * alternative runtime patching
+ * inspired by the x86 version
+ *
+ * Copyright (C) 2014 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#define pr_fmt(fmt) "alternatives: " fmt
+
+#include <linux/init.h>
+#include <linux/cpu.h>
+#include <asm/cacheflush.h>
+#include <asm/alternative.h>
+#include <asm/cpufeature.h>
+#include <linux/stop_machine.h>
+
+extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
+
+static int __apply_alternatives(void *dummy)
+{
+	struct alt_instr *alt;
+	u8 *origptr, *replptr;
+
+	for (alt = __alt_instructions; alt < __alt_instructions_end; alt++) {
+		if (!cpus_have_cap(alt->cpufeature))
+			continue;
+
+		BUG_ON(alt->alt_len > alt->orig_len);
+
+		pr_info_once("patching kernel code\n");
+
+		origptr = (u8 *)&alt->orig_offset + alt->orig_offset;
+		replptr = (u8 *)&alt->alt_offset + alt->alt_offset;
+		memcpy(origptr, replptr, alt->alt_len);
+		flush_icache_range((uintptr_t)origptr,
+				   (uintptr_t)(origptr + alt->alt_len));
+	}
+
+	return 0;
+}
+
+void apply_alternatives(void)
+{
+	/* better not try code patching on a live SMP system */
+	stop_machine(__apply_alternatives, NULL, NULL);
+}
+
+void free_alternatives_memory(void)
+{
+	free_reserved_area(__alt_instructions, __alt_instructions_end,
+			   0, "alternatives");
+}