linux-kernel - [PATCH v4 3/9] riscv: patch code by fixmap mapping

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Message-Id: <0b6ad2759b47731a83008b46dbbed7c92e68cae2.1586265122.git.zong.li@sifive.com>
Date:   Tue,  7 Apr 2020 22:46:48 +0800
From:   Zong Li <zong.li@...ive.com>
To:     palmer@...belt.com, paul.walmsley@...ive.com,
        aou@...s.berkeley.edu, mhiramat@...nel.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Zong Li <zong.li@...ive.com>
Subject: [PATCH v4 3/9] riscv: patch code by fixmap mapping

On strict kernel memory permission, the ftrace have to change the
permission of text for dynamic patching the intructions. Use
riscv_patch_text_nosync() to patch code instead of probe_kernel_write.

Signed-off-by: Zong Li <zong.li@...ive.com>
Suggested-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 arch/riscv/kernel/ftrace.c | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index c40fdcdeb950..08396614d6f4 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -7,9 +7,23 @@
 
 #include <linux/ftrace.h>
 #include <linux/uaccess.h>
+#include <linux/memory.h>
 #include <asm/cacheflush.h>
+#include <asm/patch.h>
 
 #ifdef CONFIG_DYNAMIC_FTRACE
+int ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex)
+{
+	mutex_lock(&text_mutex);
+	return 0;
+}
+
+int ftrace_arch_code_modify_post_process(void) __releases(&text_mutex)
+{
+	mutex_unlock(&text_mutex);
+	return 0;
+}
+
 static int ftrace_check_current_call(unsigned long hook_pos,
 				     unsigned int *expected)
 {
@@ -46,20 +60,14 @@ static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
 {
 	unsigned int call[2];
 	unsigned int nops[2] = {NOP4, NOP4};
-	int ret = 0;
 
 	make_call(hook_pos, target, call);
 
-	/* replace the auipc-jalr pair at once */
-	ret = probe_kernel_write((void *)hook_pos, enable ? call : nops,
-				 MCOUNT_INSN_SIZE);
-	/* return must be -EPERM on write error */
-	if (ret)
+	/* Replace the auipc-jalr pair at once. Return -EPERM on write error. */
+	if (patch_text_nosync
+	    ((void *)hook_pos, enable ? call : nops, MCOUNT_INSN_SIZE))
 		return -EPERM;
 
-	smp_mb();
-	flush_icache_range((void *)hook_pos, (void *)hook_pos + MCOUNT_INSN_SIZE);
-
 	return 0;
 }
 
-- 
2.26.0