linux-kernel - [PATCH v6 2/5] LoongArch: Use stop_machine

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Date:   Wed, 30 Nov 2022 16:19:33 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Masami Hiramatsu <mhiramat@...nel.org>
Cc:     loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: [PATCH v6 2/5] LoongArch: Use stop_machine_cpuslocked() to modify instruction

Rename the current larch_insn_patch_text() to patch_text_nosync(),
then redefine larch_insn_patch_text() with stop_machine_cpuslocked()
to modify instruction to avoid CPU race, this is preparation for later
patch.

Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
 arch/loongarch/kernel/inst.c | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/kernel/inst.c b/arch/loongarch/kernel/inst.c
index aaaf9de..d842405 100644
--- a/arch/loongarch/kernel/inst.c
+++ b/arch/loongarch/kernel/inst.c
@@ -3,6 +3,7 @@
  * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
  */
 #include <linux/sizes.h>
+#include <linux/stop_machine.h>
 #include <linux/uaccess.h>
 
 #include <asm/cacheflush.h>
@@ -10,6 +11,12 @@
 
 static DEFINE_RAW_SPINLOCK(patch_lock);
 
+struct patch_insn {
+	void *addr;
+	u32 insn;
+	atomic_t cpu_count;
+};
+
 int larch_insn_read(void *addr, u32 *insnp)
 {
 	int ret;
@@ -34,7 +41,7 @@ int larch_insn_write(void *addr, u32 insn)
 	return ret;
 }
 
-int larch_insn_patch_text(void *addr, u32 insn)
+static int patch_text_nosync(void *addr, u32 insn)
 {
 	int ret;
 	u32 *tp = addr;
@@ -50,6 +57,30 @@ int larch_insn_patch_text(void *addr, u32 insn)
 	return ret;
 }
 
+static int patch_text_cb(void *data)
+{
+	struct patch_insn *param = data;
+	int ret = 0;
+
+	if (atomic_inc_return(&param->cpu_count) == num_online_cpus()) {
+		ret = patch_text_nosync(param->addr, param->insn);
+		atomic_inc(&param->cpu_count);
+	} else {
+		while (atomic_read(&param->cpu_count) <= num_online_cpus())
+			cpu_relax();
+		smp_mb();
+	}
+
+	return ret;
+}
+
+int larch_insn_patch_text(void *addr, u32 insn)
+{
+	struct patch_insn param = { addr, insn, ATOMIC_INIT(0) };
+
+	return stop_machine_cpuslocked(patch_text_cb, &param, cpu_online_mask);
+}
+
 u32 larch_insn_gen_nop(void)
 {
 	return INSN_NOP;
-- 
2.1.0