Re: Missing operand for tlbie instruction on Power7

[Michael Ellerman <mpe@ellerman.id.au>]

On Wed, 2015-10-07 at 20:15 -0400, Josh Boyer wrote:
> On Wed, Oct 7, 2015 at 8:10 PM, Michael Ellerman <mpe@ellerman.id.au> wrote:
> > On Wed, 2015-10-07 at 10:31 -0400, Josh Boyer wrote:
> >> On Wed, Oct 7, 2015 at 5:13 AM, Michael Ellerman <mpe@ellerman.id.au> wrote:
> >> > On Wed, 2015-10-07 at 02:19 -0500, Segher Boessenkool wrote:
> >> >> On Wed, Oct 07, 2015 at 05:00:49PM +1100, Michael Ellerman wrote:
> >> >> > > It's also worth noting that the __flush_power7 uses tlbiel instead of tlbie.
> >> >> >
> >> >> > Yeah that's a good point. It's not clear if the swsusp code wants to a local or
> >> >> > a global invalidate.
> >> >>
> >> >> If I read the code right, this is called on the boot CPU when all the
> >> >> non-boot CPUs are still (potentially) down, so if you would do a global
> >> >> invalidate the non-boot CPUs might not even notice, so those need to do
> >> >> a (local) invalidate after being brought up anyway?  Or they probably
> >> >> need it before being brought down at all?  You figure it out, it makes
> >> >> my brain hurt :-)
> >> >
> >> > A good rule would be that every cpu does a local invalidate before turning on
> >> > the MMU. That would work for this case and also for kexec, kdump, junk left by
> >> > firmare etc. But I don't think we do that consistently in a way that works for
> >> > this code at the moment.
> >> >
> >> >> > As an alternative, can you try adding a .machine push / .machine "power4" /
> >> >> > .machine pop, around the tlbie. That should tell the assembler to drop back to
> >> >> > power4 mode for that instruction, which should then do the right thing. There
> >> >> > are some examples in that file.
> >> >>
> >> >> That will get the assembler to not complain, but it will assemble the wrong
> >> >> instruction: the power7 instruction has the same opcode (but different
> >> >> semantics).  So if you assemble a "tlbie r4" in power4 mode, a newer CPU
> >> >> will see it as a "tlbie r4,r0" and do the wrong thing.
> >> >
> >> > Yeah, it would basically maintain the existing behaviour which is wrong but a
> >> > known quantity. I suspect no one has ever run this on Power7 or in fact
> >> > anything other than G5 or Book3E.
> >>
> >> Likely not, but leaving it broken just because it is known behavior
> >> seems pretty weird to me.
> >
> > In a universe where I have infinite time to fix random things we would
> > obviously do a proper fix :)
> >
> >> I think Fedora will look at simply disabling hibernation on ppc64 so the file
> >> isn't built at all.  Seems to be a safer option.
> >
> > It's safer for sure. Though you might have some G5 users who are using it and
> > notice it being disabled.
> 
> The 5 of them will notice it being disabled and then they'll realize
> they either get a working kernel minus hibernation, or they get no
> kernel at all because it doesn't compile.

Sure. But if we do the machine push thing they'll get both :)

And I doubt it's 5, 2 is more likely.

cheers