x86_64, ftrace: Make ftrace use kernel identity mapping to modify code

On x86_64, kernel text mappings are mapped read-only with
CONFIG_DEBUG_RODATA. So use the kernel identity mapping instead
of the kernel text mapping to modify the kernel text.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <20091029024821.080941108@sbs-t61.sc.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 9dbb527..944e982 100644 (file)
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -187,9 +187,26 @@ static void wait_for_nmi(void)
        nmi_wait_count++;
 }
 
+static inline int
+within(unsigned long addr, unsigned long start, unsigned long end)
+{
+       return addr >= start && addr < end;
+}
+
 static int
 do_ftrace_mod_code(unsigned long ip, void *new_code)
 {
+       /*
+        * On x86_64, kernel text mappings are mapped read-only with
+        * CONFIG_DEBUG_RODATA. So we use the kernel identity mapping instead
+        * of the kernel text mapping to modify the kernel text.
+        *
+        * For 32bit kernels, these mappings are same and we can use
+        * kernel identity mapping to modify code.
+        */
+       if (within(ip, (unsigned long)_text, (unsigned long)_etext))
+               ip = (unsigned long)__va(__pa(ip));
+
        mod_code_ip = (void *)ip;
        mod_code_newcode = new_code;
 

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 8d1e8d9..09a140c 100644 (file)
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -279,8 +279,7 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address,
                   __pa((unsigned long)__end_rodata) >> PAGE_SHIFT))
                pgprot_val(forbidden) |= _PAGE_RW;
 
-#if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA) && \
-       !defined(CONFIG_DYNAMIC_FTRACE)
+#if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA)
        /*
         * Once the kernel maps the text as RO (kernel_set_to_readonly is set),
         * kernel text mappings for the large page aligned text, rodata sections