Messages in this thread Patch in this message | | | Subject | Re: [PATCH] [GIT PULL] tracing: allow to change permissions for text with dynamic ftrace enabled | From | Suresh Siddha <> | Date | Tue, 27 Oct 2009 14:26:04 -0800 |
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On Tue, 2009-10-27 at 11:33 -0700, Steven Rostedt wrote: > On Tue, 2009-10-27 at 11:20 -0800, Suresh Siddha wrote: > > > Steven, Is it possible for dynamic ftrace to use the kernel identity > > mapping instead of the kernel text mapping for converting the tracing > > calls to nops etc. > > Not sure what you mean by "kernel identity" mapping.
64bit has the kernel text pages mapped at two locations. kernel identity mapping (__PAGE_OFFSET) and kernel image/text mapping (__START_KERNEL_map).
DEBUG_RODATA patch was trying to preserve large page mapping (for perf reasons) for kernel text. We can use the identity mapping for modifying the kernel text.
This patch seems to fix.
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c index 5a1b975..7e1799b 100644 --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -215,6 +215,11 @@ do_ftrace_mod_code(unsigned long ip, void *new_code) } +static inline int +within(unsigned long addr, unsigned long start, unsigned long end) +{ + return addr >= start && addr < end; +} static unsigned char ftrace_nop[MCOUNT_INSN_SIZE]; @@ -248,6 +253,14 @@ ftrace_modify_code(unsigned long ip, unsigned char *old_code, if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0) return -EINVAL; + /* + * On x86_64, we use the kernel identity mapping instead of the + * kernel text mapping to modify the kernel text. This is a nop + * for 32bit kernels. + */ + if (within(ip, (unsigned long)_text, (unsigned long)_etext)) + ip = (unsigned long)__va(__pa(ip)); + /* replace the text with the new text */ if (do_ftrace_mod_code(ip, new_code)) return -EPERM;
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