File-copy from v4.4.100
This is the result of 'cp' from a linux-stable tree with the 'v4.4.100'
tag checked out (commit 26d6298789e695c9f627ce49a7bbd2286405798a) on
git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
Please refer to that tree for all history prior to this point.
Change-Id: I8a9ee2aea93cd29c52c847d0ce33091a73ae6afe
diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c
new file mode 100644
index 0000000..ab9db0e
--- /dev/null
+++ b/arch/arm64/kernel/alternative.c
@@ -0,0 +1,166 @@
+/*
+ * 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 <asm/insn.h>
+#include <linux/stop_machine.h>
+
+#define __ALT_PTR(a,f) (u32 *)((void *)&(a)->f + (a)->f)
+#define ALT_ORIG_PTR(a) __ALT_PTR(a, orig_offset)
+#define ALT_REPL_PTR(a) __ALT_PTR(a, alt_offset)
+
+extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
+
+struct alt_region {
+ struct alt_instr *begin;
+ struct alt_instr *end;
+};
+
+/*
+ * Check if the target PC is within an alternative block.
+ */
+static bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc)
+{
+ unsigned long replptr;
+
+ if (kernel_text_address(pc))
+ return 1;
+
+ replptr = (unsigned long)ALT_REPL_PTR(alt);
+ if (pc >= replptr && pc <= (replptr + alt->alt_len))
+ return 0;
+
+ /*
+ * Branching into *another* alternate sequence is doomed, and
+ * we're not even trying to fix it up.
+ */
+ BUG();
+}
+
+static u32 get_alt_insn(struct alt_instr *alt, u32 *insnptr, u32 *altinsnptr)
+{
+ u32 insn;
+
+ insn = le32_to_cpu(*altinsnptr);
+
+ if (aarch64_insn_is_branch_imm(insn)) {
+ s32 offset = aarch64_get_branch_offset(insn);
+ unsigned long target;
+
+ target = (unsigned long)altinsnptr + offset;
+
+ /*
+ * If we're branching inside the alternate sequence,
+ * do not rewrite the instruction, as it is already
+ * correct. Otherwise, generate the new instruction.
+ */
+ if (branch_insn_requires_update(alt, target)) {
+ offset = target - (unsigned long)insnptr;
+ insn = aarch64_set_branch_offset(insn, offset);
+ }
+ }
+
+ return insn;
+}
+
+static void __apply_alternatives(void *alt_region)
+{
+ struct alt_instr *alt;
+ struct alt_region *region = alt_region;
+ u32 *origptr, *replptr;
+
+ for (alt = region->begin; alt < region->end; alt++) {
+ u32 insn;
+ int i, nr_inst;
+
+ if (!cpus_have_cap(alt->cpufeature))
+ continue;
+
+ BUG_ON(alt->alt_len != alt->orig_len);
+
+ pr_info_once("patching kernel code\n");
+
+ origptr = ALT_ORIG_PTR(alt);
+ replptr = ALT_REPL_PTR(alt);
+ nr_inst = alt->alt_len / sizeof(insn);
+
+ for (i = 0; i < nr_inst; i++) {
+ insn = get_alt_insn(alt, origptr + i, replptr + i);
+ *(origptr + i) = cpu_to_le32(insn);
+ }
+
+ flush_icache_range((uintptr_t)origptr,
+ (uintptr_t)(origptr + nr_inst));
+ }
+}
+
+/*
+ * We might be patching the stop_machine state machine, so implement a
+ * really simple polling protocol here.
+ */
+static int __apply_alternatives_multi_stop(void *unused)
+{
+ static int patched = 0;
+ struct alt_region region = {
+ .begin = __alt_instructions,
+ .end = __alt_instructions_end,
+ };
+
+ /* We always have a CPU 0 at this point (__init) */
+ if (smp_processor_id()) {
+ while (!READ_ONCE(patched))
+ cpu_relax();
+ isb();
+ } else {
+ BUG_ON(patched);
+ __apply_alternatives(®ion);
+ /* Barriers provided by the cache flushing */
+ WRITE_ONCE(patched, 1);
+ }
+
+ return 0;
+}
+
+void __init apply_alternatives_all(void)
+{
+ /* better not try code patching on a live SMP system */
+ stop_machine(__apply_alternatives_multi_stop, NULL, cpu_online_mask);
+}
+
+void apply_alternatives(void *start, size_t length)
+{
+ struct alt_region region = {
+ .begin = start,
+ .end = start + length,
+ };
+
+ __apply_alternatives(®ion);
+}
+
+void free_alternatives_memory(void)
+{
+ free_reserved_area(__alt_instructions, __alt_instructions_end,
+ 0, "alternatives");
+}