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 <[email protected]>
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: zongbox

arch/riscv/kernel/ftrace.c

@@ -8,6 +8,7 @@
 #include <linux/ftrace.h>
 #include <linux/uaccess.h>
 #include <asm/cacheflush.h>
+#include <asm/patch.h>
 
 #ifdef CONFIG_DYNAMIC_FTRACE
 static int ftrace_check_current_call(unsigned long hook_pos,
@@ -46,20 +47,14 @@ 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 (riscv_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;
 }