Re: [PATCH v3 6/6] powerpc/64s: Blacklist rtas entry/exit from kprobes

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

On 2017/06/22 01:48PM, Nicholas Piggin wrote:
> On Thu, 22 Jun 2017 00:08:42 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
> 
> > We can't take traps with relocation off, so blacklist enter_rtas() and
> > rtas_return_loc(). However, instead of blacklisting all of enter_rtas(),
> > introduce a new symbol __enter_rtas from where on we can't take a trap
> > and blacklist that.
> > 
> > Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> > ---
> >  arch/powerpc/kernel/entry_64.S | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> > index d376f07153d7..49c35450f399 100644
> > --- a/arch/powerpc/kernel/entry_64.S
> > +++ b/arch/powerpc/kernel/entry_64.S
> > @@ -1076,6 +1076,8 @@ _GLOBAL(enter_rtas)
> >          rldicr  r9,r9,MSR_SF_LG,(63-MSR_SF_LG)
> >  	ori	r9,r9,MSR_IR|MSR_DR|MSR_FE0|MSR_FE1|MSR_FP|MSR_RI|MSR_LE
> >  	andc	r6,r0,r9
> > +
> > +__enter_rtas:
> >  	sync				/* disable interrupts so SRR0/1 */
> >  	mtmsrd	r0			/* don't get trashed */
> 
> Along the lines of the system call patch... For consistency, could we
> put the __enter_rtas right after mtmsrd? And I wonder if we shoul

Sure.

> come up with a common prefix or postfix naming convention for these
> such labels used to control probing?

We could, but I am not sure it will help much. On the other hand, such 
symbols may make backtraces pretty distracting.

I'm just using '__' as a prefix to make it less distracting, though it 
isn't all that great either. I'm clearly hopeless with names o_O

The other option is to just blacklist entire functions, but we will then 
lose the ability to probe in many places where we may have wanted to.

> 
> How do opal calls avoid tracing?

It doesn't yet. I'm still going through the initial few symbols and 
identifying what needs blacklisting. Opal is further down.

Thanks,
Naveen