1 files changed, 79 insertions, 45 deletions

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index ab115cd15fdf..d073d981a730 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -11,17 +11,18 @@
 
 #include <linux/spinlock.h>
 #include <linux/hardirq.h>
+#include <linux/uaccess.h>
 #include <linux/ftrace.h>
 #include <linux/percpu.h>
 #include <linux/init.h>
 #include <linux/list.h>
 
-#include <asm/alternative.h>
 #include <asm/ftrace.h>
+#include <asm/nops.h>
 
 
 /* Long is fine, even if it is only 4 bytes ;-) */
-static long *ftrace_nop;
+static unsigned long *ftrace_nop;
 
 union ftrace_code_union {
         char code[MCOUNT_INSN_SIZE];
@@ -60,11 +61,7 @@ notrace int
 ftrace_modify_code(unsigned long ip, unsigned char *old_code,
                    unsigned char *new_code)
 {
-        unsigned replaced;
-        unsigned old = *(unsigned *)old_code; /* 4 bytes */
-        unsigned new = *(unsigned *)new_code; /* 4 bytes */
-        unsigned char newch = new_code[4];
-        int faulted = 0;
+        unsigned char replaced[MCOUNT_INSN_SIZE];
 
         /*
          * Note: Due to modules and __init, code can
@@ -72,29 +69,20 @@ ftrace_modify_code(unsigned long ip, unsigned char *old_code,
          *  as well as code changing.
          *
          * No real locking needed, this code is run through
-         * kstop_machine.
+         * kstop_machine, or before SMP starts.
          */
-        asm volatile (
-                "1: lock\n"
-                "   cmpxchg %3, (%2)\n"
-                "   jnz 2f\n"
-                "   movb %b4, 4(%2)\n"
-                "2:\n"
-                ".section .fixup, \"ax\"\n"
-                "3:     movl $1, %0\n"
-                "       jmp 2b\n"
-                ".previous\n"
-                _ASM_EXTABLE(1b, 3b)
-                : "=r"(faulted), "=a"(replaced)
-                : "r"(ip), "r"(new), "c"(newch),
-                  "0"(faulted), "a"(old)
-                : "memory");
-        sync_core();
+        if (__copy_from_user_inatomic(replaced, (char __user *)ip, MCOUNT_INSN_SIZE))
+                return 1;
+
+        if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
+                return 2;
 
-        if (replaced != old && replaced != new)
-                faulted = 2;
+        WARN_ON_ONCE(__copy_to_user_inatomic((char __user *)ip, new_code,
+                                    MCOUNT_INSN_SIZE));
 
-        return faulted;
+        sync_core();
+
+        return 0;
 }
 
 notrace int ftrace_update_ftrace_func(ftrace_func_t func)
@@ -112,30 +100,76 @@ notrace int ftrace_update_ftrace_func(ftrace_func_t func)
 
 notrace int ftrace_mcount_set(unsigned long *data)
 {
-        unsigned long ip = (long)(&mcount_call);
-        unsigned long *addr = data;
-        unsigned char old[MCOUNT_INSN_SIZE], *new;
-
-        /*
-         * Replace the mcount stub with a pointer to the
-         * ip recorder function.
-         */
-        memcpy(old, &mcount_call, MCOUNT_INSN_SIZE);
-        new = ftrace_call_replace(ip, *addr);
-        *addr = ftrace_modify_code(ip, old, new);
-
+        /* mcount is initialized as a nop */
+        *data = 0;
         return 0;
 }
 
 int __init ftrace_dyn_arch_init(void *data)
 {
-        const unsigned char *const *noptable = find_nop_table();
-
-        /* This is running in kstop_machine */
-
-        ftrace_mcount_set(data);
+        extern const unsigned char ftrace_test_p6nop[];
+        extern const unsigned char ftrace_test_nop5[];
+        extern const unsigned char ftrace_test_jmp[];
+        int faulted = 0;
 
-        ftrace_nop = (unsigned long *)noptable[MCOUNT_INSN_SIZE];
+        /*
+         * There is no good nop for all x86 archs.
+         * We will default to using the P6_NOP5, but first we
+         * will test to make sure that the nop will actually
+         * work on this CPU. If it faults, we will then
+         * go to a lesser efficient 5 byte nop. If that fails
+         * we then just use a jmp as our nop. This isn't the most
+         * efficient nop, but we can not use a multi part nop
+         * since we would then risk being preempted in the middle
+         * of that nop, and if we enabled tracing then, it might
+         * cause a system crash.
+         *
+         * TODO: check the cpuid to determine the best nop.
+         */
+        asm volatile (
+                "jmp ftrace_test_jmp\n"
+                /* This code needs to stay around */
+                ".section .text, \"ax\"\n"
+                "ftrace_test_jmp:"
+                "jmp ftrace_test_p6nop\n"
+                "nop\n"
+                "nop\n"
+                "nop\n"  /* 2 byte jmp + 3 bytes */
+                "ftrace_test_p6nop:"
+                P6_NOP5
+                "jmp 1f\n"
+                "ftrace_test_nop5:"
+                ".byte 0x66,0x66,0x66,0x66,0x90\n"
+                "jmp 1f\n"
+                ".previous\n"
+                "1:"
+                ".section .fixup, \"ax\"\n"
+                "2:     movl $1, %0\n"
+                "       jmp ftrace_test_nop5\n"
+                "3:     movl $2, %0\n"
+                "       jmp 1b\n"
+                ".previous\n"
+                _ASM_EXTABLE(ftrace_test_p6nop, 2b)
+                _ASM_EXTABLE(ftrace_test_nop5, 3b)
+                : "=r"(faulted) : "0" (faulted));
+
+        switch (faulted) {
+        case 0:
+                pr_info("ftrace: converting mcount calls to 0f 1f 44 00 00\n");
+                ftrace_nop = (unsigned long *)ftrace_test_p6nop;
+                break;
+        case 1:
+                pr_info("ftrace: converting mcount calls to 66 66 66 66 90\n");
+                ftrace_nop = (unsigned long *)ftrace_test_nop5;
+                break;
+        case 2:
+                pr_info("ftrace: converting mcount calls to jmp . + 5\n");
+                ftrace_nop = (unsigned long *)ftrace_test_jmp;
+                break;
+        }
+
+        /* The return code is retured via data */
+        *(unsigned long *)data = 0;
 
         return 0;
 }