powerpc: ftrace, use probe_kernel API to modify code

Impact: use cleaner probe_kernel API over assembly

Using probe_kernel_read/write interface is a much cleaner approach
than the current assembly version.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

1 files changed, 21 insertions, 32 deletions

diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index 24c023a5cae8..1adfbb268d8e 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -9,6 +9,7 @@
 
 #include <linux/spinlock.h>
 #include <linux/hardirq.h>
+#include <linux/uaccess.h>
 #include <linux/ftrace.h>
 #include <linux/percpu.h>
 #include <linux/init.h>
@@ -72,45 +73,33 @@ static int
 ftrace_modify_code(unsigned long ip, unsigned char *old_code,
                    unsigned char *new_code)
 {
-        unsigned replaced;
-        unsigned old = *(unsigned *)old_code;
-        unsigned new = *(unsigned *)new_code;
-        int faulted = 0;
+        unsigned char replaced[MCOUNT_INSN_SIZE];
 
         /*
          * Note: Due to modules and __init, code can
          *  disappear and change, we need to protect against faulting
-         *  as well as code changing.
+         *  as well as code changing. We do this by using the
+         *  probe_kernel_* functions.
          *
          * No real locking needed, this code is run through
-         * kstop_machine.
+         * kstop_machine, or before SMP starts.
          */
-        asm volatile (
-                "1: lwz         %1, 0(%2)\n"
-                "   cmpw        %1, %5\n"
-                "   bne         2f\n"
-                "   stwu        %3, 0(%2)\n"
-                "2:\n"
-                ".section .fixup, \"ax\"\n"
-                "3:     li %0, 1\n"
-                "       b 2b\n"
-                ".previous\n"
-                ".section __ex_table,\"a\"\n"
-                _ASM_ALIGN "\n"
-                _ASM_PTR "1b, 3b\n"
-                ".previous"
-                : "=r"(faulted), "=r"(replaced)
-                : "r"(ip), "r"(new),
-                  "0"(faulted), "r"(old)
-                : "memory");
-
-        if (replaced != old && replaced != new)
-                faulted = 2;
-
-        if (!faulted)
-                flush_icache_range(ip, ip + 8);
-
-        return faulted;
+
+        /* read the text we want to modify */
+        if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
+                return -EFAULT;
+
+        /* Make sure it is what we expect it to be */
+        if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
+                return -EINVAL;
+
+        /* replace the text with the new text */
+        if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE))
+                return -EPERM;
+
+        flush_icache_range(ip, ip + 8);
+
+        return 0;
 }
 
 static int test_24bit_addr(unsigned long ip, unsigned long addr)