On Thu, 22 Jun 2017 00:08:40 +0530 "Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> wrote:
> It is actually safe to probe system_call() in entry_64.S, but only till > we unset MSR_RI. To allow this, add a new symbol system_call_exit() > after the mtmsrd and blacklist that. Though the mtmsrd instruction > itself is now whitelisted, we won't be allowed to probe on it as we > don't allow probing on rfi and mtmsr instructions (checked for in > arch_prepare_kprobe()). Can you add a little comment to say probes aren't allowed, and it's located after the mtmsr in order to avoid contaminating traces? Also I wonder if a slightly different name would be more instructive? I don't normally care, but the system_call_common code isn't trivial to follow. system_call_exit might give the impression that it is the entire exit path (which would pair with system_call for entry). Perhaps system_call_exit_notrace? No that sucks too :( Thanks, Nick > > Suggested-by: Michael Ellerman <m...@ellerman.id.au> > Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com> > --- > arch/powerpc/kernel/entry_64.S | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S > index ef8e6615b8ba..feeeadc9aa71 100644 > --- a/arch/powerpc/kernel/entry_64.S > +++ b/arch/powerpc/kernel/entry_64.S > @@ -204,6 +204,7 @@ system_call: /* label this so stack > traces look sane */ > mtmsrd r11,1 > #endif /* CONFIG_PPC_BOOK3E */ > > +system_call_exit: > ld r9,TI_FLAGS(r12) > li r11,-MAX_ERRNO > andi. > r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK) > @@ -412,7 +413,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR) > b . /* prevent speculative execution */ > #endif > _ASM_NOKPROBE_SYMBOL(system_call_common); > -_ASM_NOKPROBE_SYMBOL(system_call); > +_ASM_NOKPROBE_SYMBOL(system_call_exit); > > /* Save non-volatile GPRs, if not already saved. */ > _GLOBAL(save_nvgprs)
