Re: [PATCH 1/2 v2] ftrace/x86: Have arch x86_64 use breakpointsinstead of stop machine

[Masami Hiramatsu]

(2012/04/27 2:34), Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@xxxxxxxxxx>
> 
> This method changes x86 to add a breakpoint to the mcount locations
> instead of calling stop machine.
> 
> Now that iret can be handled by NMIs, we perform the following to
> update code:
> 
> 1) Add a breakpoint to all locations that will be modified
> 
> 2) Sync all cores
> 
> 3) Update all locations to be either a nop or call (except breakpoint
>    op)
> 
> 4) Sync all cores
> 
> 5) Remove the breakpoint with the new code.
> 
> 6) Sync all cores
> 
> [
>   Added updates that Masami suggested:
>    Use unlikely(modifying_ftrace_code) in int3 trap to keep kprobes efficient.
>    Don't use NOTIFY_* in ftrace handler in int3 as it is not a notifier.
> ]

This looks good to me :)

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>

> 
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
> Cc: H. Peter Anvin <hpa@xxxxxxxxx>
> Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
> ---
>  arch/x86/include/asm/ftrace.h |    3 +
>  arch/x86/kernel/ftrace.c      |  342 +++++++++++++++++++++++++++++++++++++++++
>  arch/x86/kernel/traps.c       |    8 +-
>  include/linux/ftrace.h        |    6 +
>  4 files changed, 358 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
> index 268c783..18d9005 100644
> --- a/arch/x86/include/asm/ftrace.h
> +++ b/arch/x86/include/asm/ftrace.h
> @@ -34,6 +34,7 @@
>  
>  #ifndef __ASSEMBLY__
>  extern void mcount(void);
> +extern int modifying_ftrace_code;
>  
>  static inline unsigned long ftrace_call_adjust(unsigned long addr)
>  {
> @@ -50,6 +51,8 @@ struct dyn_arch_ftrace {
>  	/* No extra data needed for x86 */
>  };
>  
> +int ftrace_int3_handler(struct pt_regs *regs);
> +
>  #endif /*  CONFIG_DYNAMIC_FTRACE */
>  #endif /* __ASSEMBLY__ */
>  #endif /* CONFIG_FUNCTION_TRACER */
> diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
> index c9a281f..80af347 100644
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -20,6 +20,7 @@
>  #include <linux/init.h>
>  #include <linux/list.h>
>  #include <linux/module.h>
> +#include <linux/kprobes.h>
>  
>  #include <trace/syscall.h>
>  
> @@ -334,6 +335,347 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
>  	return ret;
>  }
>  
> +int modifying_ftrace_code __read_mostly;
> +
> +/*
> + * A breakpoint was added to the code address we are about to
> + * modify, and this is the handle that will just skip over it.
> + * We are either changing a nop into a trace call, or a trace
> + * call to a nop. While the change is taking place, we treat
> + * it just like it was a nop.
> + */
> +int ftrace_int3_handler(struct pt_regs *regs)
> +{
> +	if (WARN_ON_ONCE(!regs))
> +		return 0;
> +
> +	if (!ftrace_location(regs->ip - 1))
> +		return 0;
> +
> +	regs->ip += MCOUNT_INSN_SIZE - 1;
> +
> +	return 1;
> +}
> +
> +static int ftrace_write(unsigned long ip, const char *val, int size)
> +{
> +	/*
> +	 * 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));
> +
> +	return probe_kernel_write((void *)ip, val, size);
> +}
> +
> +static int add_break(unsigned long ip, const char *old)
> +{
> +	unsigned char replaced[MCOUNT_INSN_SIZE];
> +	unsigned char brk = BREAKPOINT_INSTRUCTION;
> +
> +	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, MCOUNT_INSN_SIZE) != 0)
> +		return -EINVAL;
> +
> +	if (ftrace_write(ip, &brk, 1))
> +		return -EPERM;
> +
> +	return 0;
> +}
> +
> +static int add_brk_on_call(struct dyn_ftrace *rec, unsigned long addr)
> +{
> +	unsigned const char *old;
> +	unsigned long ip = rec->ip;
> +
> +	old = ftrace_call_replace(ip, addr);
> +
> +	return add_break(rec->ip, old);
> +}
> +
> +
> +static int add_brk_on_nop(struct dyn_ftrace *rec)
> +{
> +	unsigned const char *old;
> +
> +	old = ftrace_nop_replace();
> +
> +	return add_break(rec->ip, old);
> +}
> +
> +static int add_breakpoints(struct dyn_ftrace *rec, int enable)
> +{
> +	unsigned long ftrace_addr;
> +	int ret;
> +
> +	ret = ftrace_test_record(rec, enable);
> +
> +	ftrace_addr = (unsigned long)FTRACE_ADDR;
> +
> +	switch (ret) {
> +	case FTRACE_UPDATE_IGNORE:
> +		return 0;
> +
> +	case FTRACE_UPDATE_MAKE_CALL:
> +		/* converting nop to call */
> +		return add_brk_on_nop(rec);
> +
> +	case FTRACE_UPDATE_MAKE_NOP:
> +		/* converting a call to a nop */
> +		return add_brk_on_call(rec, ftrace_addr);
> +	}
> +	return 0;
> +}
> +
> +/*
> + * On error, we need to remove breakpoints. This needs to
> + * be done caefully. If the address does not currently have a
> + * breakpoint, we know we are done. Otherwise, we look at the
> + * remaining 4 bytes of the instruction. If it matches a nop
> + * we replace the breakpoint with the nop. Otherwise we replace
> + * it with the call instruction.
> + */
> +static int remove_breakpoint(struct dyn_ftrace *rec)
> +{
> +	unsigned char ins[MCOUNT_INSN_SIZE];
> +	unsigned char brk = BREAKPOINT_INSTRUCTION;
> +	const unsigned char *nop;
> +	unsigned long ftrace_addr;
> +	unsigned long ip = rec->ip;
> +
> +	/* If we fail the read, just give up */
> +	if (probe_kernel_read(ins, (void *)ip, MCOUNT_INSN_SIZE))
> +		return -EFAULT;
> +
> +	/* If this does not have a breakpoint, we are done */
> +	if (ins[0] != brk)
> +		return -1;
> +
> +	nop = ftrace_nop_replace();
> +
> +	/*
> +	 * If the last 4 bytes of the instruction do not match
> +	 * a nop, then we assume that this is a call to ftrace_addr.
> +	 */
> +	if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0) {
> +		/*
> +		 * For extra paranoidism, we check if the breakpoint is on
> +		 * a call that would actually jump to the ftrace_addr.
> +		 * If not, don't touch the breakpoint, we make just create
> +		 * a disaster.
> +		 */
> +		ftrace_addr = (unsigned long)FTRACE_ADDR;
> +		nop = ftrace_call_replace(ip, ftrace_addr);
> +
> +		if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0)
> +			return -EINVAL;
> +	}
> +
> +	return probe_kernel_write((void *)ip, &nop[0], 1);
> +}
> +
> +static int add_update_code(unsigned long ip, unsigned const char *new)
> +{
> +	/* skip breakpoint */
> +	ip++;
> +	new++;
> +	if (ftrace_write(ip, new, MCOUNT_INSN_SIZE - 1))
> +		return -EPERM;
> +	return 0;
> +}
> +
> +static int add_update_call(struct dyn_ftrace *rec, unsigned long addr)
> +{
> +	unsigned long ip = rec->ip;
> +	unsigned const char *new;
> +
> +	new = ftrace_call_replace(ip, addr);
> +	return add_update_code(ip, new);
> +}
> +
> +static int add_update_nop(struct dyn_ftrace *rec)
> +{
> +	unsigned long ip = rec->ip;
> +	unsigned const char *new;
> +
> +	new = ftrace_nop_replace();
> +	return add_update_code(ip, new);
> +}
> +
> +static int add_update(struct dyn_ftrace *rec, int enable)
> +{
> +	unsigned long ftrace_addr;
> +	int ret;
> +
> +	ret = ftrace_test_record(rec, enable);
> +
> +	ftrace_addr = (unsigned long)FTRACE_ADDR;
> +
> +	switch (ret) {
> +	case FTRACE_UPDATE_IGNORE:
> +		return 0;
> +
> +	case FTRACE_UPDATE_MAKE_CALL:
> +		/* converting nop to call */
> +		return add_update_call(rec, ftrace_addr);
> +
> +	case FTRACE_UPDATE_MAKE_NOP:
> +		/* converting a call to a nop */
> +		return add_update_nop(rec);
> +	}
> +
> +	return 0;
> +}
> +
> +static int finish_update_call(struct dyn_ftrace *rec, unsigned long addr)
> +{
> +	unsigned long ip = rec->ip;
> +	unsigned const char *new;
> +
> +	new = ftrace_call_replace(ip, addr);
> +
> +	if (ftrace_write(ip, new, 1))
> +		return -EPERM;
> +
> +	return 0;
> +}
> +
> +static int finish_update_nop(struct dyn_ftrace *rec)
> +{
> +	unsigned long ip = rec->ip;
> +	unsigned const char *new;
> +
> +	new = ftrace_nop_replace();
> +
> +	if (ftrace_write(ip, new, 1))
> +		return -EPERM;
> +	return 0;
> +}
> +
> +static int finish_update(struct dyn_ftrace *rec, int enable)
> +{
> +	unsigned long ftrace_addr;
> +	int ret;
> +
> +	ret = ftrace_update_record(rec, enable);
> +
> +	ftrace_addr = (unsigned long)FTRACE_ADDR;
> +
> +	switch (ret) {
> +	case FTRACE_UPDATE_IGNORE:
> +		return 0;
> +
> +	case FTRACE_UPDATE_MAKE_CALL:
> +		/* converting nop to call */
> +		return finish_update_call(rec, ftrace_addr);
> +
> +	case FTRACE_UPDATE_MAKE_NOP:
> +		/* converting a call to a nop */
> +		return finish_update_nop(rec);
> +	}
> +
> +	return 0;
> +}
> +
> +static void do_sync_core(void *data)
> +{
> +	sync_core();
> +}
> +
> +static void run_sync(void)
> +{
> +	int enable_irqs = irqs_disabled();
> +
> +	/* We may be called with interrupts disbled (on bootup). */
> +	if (enable_irqs)
> +		local_irq_enable();
> +	on_each_cpu(do_sync_core, NULL, 1);
> +	if (enable_irqs)
> +		local_irq_disable();
> +}
> +
> +static void ftrace_replace_code(int enable)
> +{
> +	struct ftrace_rec_iter *iter;
> +	struct dyn_ftrace *rec;
> +	const char *report = "adding breakpoints";
> +	int count = 0;
> +	int ret;
> +
> +	for_ftrace_rec_iter(iter) {
> +		rec = ftrace_rec_iter_record(iter);
> +
> +		ret = add_breakpoints(rec, enable);
> +		if (ret)
> +			goto remove_breakpoints;
> +		count++;
> +	}
> +
> +	run_sync();
> +
> +	report = "updating code";
> +
> +	for_ftrace_rec_iter(iter) {
> +		rec = ftrace_rec_iter_record(iter);
> +
> +		ret = add_update(rec, enable);
> +		if (ret)
> +			goto remove_breakpoints;
> +	}
> +
> +	run_sync();
> +
> +	report = "removing breakpoints";
> +
> +	for_ftrace_rec_iter(iter) {
> +		rec = ftrace_rec_iter_record(iter);
> +
> +		ret = finish_update(rec, enable);
> +		if (ret)
> +			goto remove_breakpoints;
> +	}
> +
> +	run_sync();
> +
> +	return;
> +
> + remove_breakpoints:
> +	ftrace_bug(ret, rec ? rec->ip : 0);
> +	printk(KERN_WARNING "Failed on %s (%d):\n", report, count);
> +	for_ftrace_rec_iter(iter) {
> +		rec = ftrace_rec_iter_record(iter);
> +		remove_breakpoint(rec);
> +	}
> +}
> +
> +void arch_ftrace_update_code(int command)
> +{
> +	modifying_ftrace_code++;
> +
> +	if (command & FTRACE_UPDATE_CALLS)
> +		ftrace_replace_code(1);
> +	else if (command & FTRACE_DISABLE_CALLS)
> +		ftrace_replace_code(0);
> +
> +	if (command & FTRACE_UPDATE_TRACE_FUNC)
> +		ftrace_update_ftrace_func(ftrace_trace_function);
> +
> +	if (command & FTRACE_START_FUNC_RET)
> +		ftrace_enable_ftrace_graph_caller();
> +	else if (command & FTRACE_STOP_FUNC_RET)
> +		ftrace_disable_ftrace_graph_caller();
> +
> +	modifying_ftrace_code--;
> +}
> +
>  int __init ftrace_dyn_arch_init(void *data)
>  {
>  	/* The return code is retured via data */
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index ff9281f1..92d5756 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -50,6 +50,7 @@
>  #include <asm/processor.h>
>  #include <asm/debugreg.h>
>  #include <linux/atomic.h>
> +#include <asm/ftrace.h>
>  #include <asm/traps.h>
>  #include <asm/desc.h>
>  #include <asm/i387.h>
> @@ -303,8 +304,13 @@ gp_in_kernel:
>  }
>  
>  /* May run on IST stack. */
> -dotraplinkage void __kprobes do_int3(struct pt_regs *regs, long error_code)
> +dotraplinkage void __kprobes notrace do_int3(struct pt_regs *regs, long error_code)
>  {
> +#ifdef CONFIG_DYNAMIC_FTRACE
> +	/* ftrace must be first, everything else may cause a recursive crash */
> +	if (unlikely(modifying_ftrace_code) && ftrace_int3_handler(regs))
> +		return;
> +#endif
>  #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
>  	if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
>  				SIGTRAP) == NOTIFY_STOP)
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 72a6cab..0b55903 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -286,6 +286,12 @@ struct ftrace_rec_iter *ftrace_rec_iter_start(void);
>  struct ftrace_rec_iter *ftrace_rec_iter_next(struct ftrace_rec_iter *iter);
>  struct dyn_ftrace *ftrace_rec_iter_record(struct ftrace_rec_iter *iter);
>  
> +#define for_ftrace_rec_iter(iter)		\
> +	for (iter = ftrace_rec_iter_start();	\
> +	     iter;				\
> +	     iter = ftrace_rec_iter_next(iter))
> +
> +
>  int ftrace_update_record(struct dyn_ftrace *rec, int enable);
>  int ftrace_test_record(struct dyn_ftrace *rec, int enable);
>  void ftrace_run_stop_machine(int command);


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx
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