On Tue, Feb 18, 2020 at 01:33:35PM +0900, Masami Hiramatsu wrote: > On Mon, 17 Feb 2020 08:31:12 -0800 > "Paul E. McKenney" <paulmck@xxxxxxxxxx> wrote: > > > > > BTW, if you consider the x86 specific code is in the generic file, > > > we can move NOKPROBE_SYMBOL() in arch/x86/kernel/traps.c. > > > (Sorry, I've hit this idea right now) > > > > Might this affect other architectures with NMIs and probe-like things? > > If so, it might make sense to leave it where it is. > > Yes, git grep shows that arm64 is using rcu_nmi_enter() in > debug_exception_enter(). > OK, let's keep it, but maybe it is good to update the comment for > arm64 too. What about following? > > +/* > + * All functions in do_int3() on x86, do_debug_exception() on arm64 must be > + * marked NOKPROBE before kprobes handler is called. > + * ist_enter() on x86 and debug_exception_enter() on arm64 which is called > + * before kprobes handle happens to call rcu_nmi_enter() which means > + * that rcu_nmi_enter() must be marked NOKRPOBE. > + */ Would it work to describe the general problem, then give x86 details as a specific example, as follows? /* * On some architectures, certain exceptions prohibit use of kprobes until * the exception code path reaches a certain point. For example, on x86 all * functions called by do_int3() must be marked NOKPROBE. However, once * kprobe_int3_handler() is called, kprobing is permitted. Specifically, * ist_enter() is called in do_int3() before kprobe_int3_handle(). * Furthermore, ist_enter() calls rcu_nmi_enter(), which means that * rcu_nmi_enter() must be marked NOKRPOBE. */ That way, I don't feel like I need to update the commment each time a new architecture adds this capability. ;-) Thanx, Paul
