Messages in this thread | | | Date | Tue, 24 Nov 2009 12:46:32 -0500 | From | Masami Hiramatsu <> | Subject | Re: [PATCH -tip v5 07/10] kprobes/x86: Support kprobes jump optimization on x86 |
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Jason Baron wrote: [...] >> +/* >> + * Cross-modifying kernel text with stop_machine(). >> + * This code originally comes from immediate value. >> + * This does _not_ protect against NMI and MCE. However, >> + * since kprobes can't probe NMI/MCE handler, it is OK for kprobes. >> + */ >> +static atomic_t stop_machine_first; >> +static int wrote_text; >> + >> +struct text_poke_param { >> + void *addr; >> + const void *opcode; >> + size_t len; >> +}; >> + >> +static int __kprobes stop_machine_multibyte_poke(void *data) >> +{ >> + struct text_poke_param *tpp = data; >> + >> + if (atomic_dec_and_test(&stop_machine_first)) { >> + text_poke(tpp->addr, tpp->opcode, tpp->len); >> + smp_wmb(); /* Make sure other cpus see that this has run */ >> + wrote_text = 1; >> + } else { >> + while (!wrote_text) >> + smp_rmb(); >> + sync_core(); >> + } >> + >> + flush_icache_range((unsigned long)tpp->addr, >> + (unsigned long)tpp->addr + tpp->len); >> + return 0; >> +} >> + >> +static void *__kprobes __multibyte_poke(void *addr, const void *opcode, >> + size_t len) >> +{ >> + struct text_poke_param tpp; >> + >> + tpp.addr = addr; >> + tpp.opcode = opcode; >> + tpp.len = len; >> + atomic_set(&stop_machine_first, 1); >> + wrote_text = 0; >> + stop_machine(stop_machine_multibyte_poke, (void *)&tpp, NULL); >> + return addr; >> +} > > As you know, I'd like to have the jump label optimization for > tracepoints, make use of this '__multibyte_poke()' interface. So perhaps > it can be moved to arch/x86/kernel/alternative.c. This is where 'text_poke()' > and friends currently live.
Hmm, maybe current text_poke needs to have singlebyte_poke() wrapper for avoiding confusion.
> Also, with multiple users we don't want to trample over each others code > patching. Thus, if each sub-system could register some type of > 'is_reserved()' callback, and then we can call all these call backs from > the '__multibyte_poke()' routine before we do any patching to make sure > that we aren't trampling on each others code. After a successful > patching, each sub-system can update its reserved set of code as > appropriate. I can code a prototype here, if this makes sense.
Hmm, we have to implement it carefully, because here kprobes already inserted int3 and optprobe rewrites the int3 again. If is_reserved() returns 1 and multibyte_poke returns error, we can't optimize it anymore.
Thank you,
-- Masami Hiramatsu
Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division
e-mail: mhiramat@redhat.com
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