On 2017/06/29 08:55PM, Nicholas Piggin wrote: > On Thu, 29 Jun 2017 16:11:08 +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 perhaps add a small comment to explain the label > (and why it's safe to have after the mtmsrd). It could be > a bit confusing to read if you don't have that detail of > the tracer in your mind.
Ah, I see. You did ask for this previously, but I thought you were just asking for a comment that this is blacklisted, which can be found out by looking for the _ASM_NOKPROBE_SYMBOL() further below. I will add a comment. Thanks, Naveen > > Other than that > > Reviewed-by: Nicholas Piggin <npig...@gmail.com> > > > > > > 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 c39436706555..7a87427a67cd 100644 > > --- a/arch/powerpc/kernel/entry_64.S > > +++ b/arch/powerpc/kernel/entry_64.S > > @@ -205,6 +205,7 @@ 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) > > @@ -413,7 +414,7 @@ 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) >
