linux-kernel - Re: Missing operand for tlbie instruction on Power7

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Message-ID: <1444209210.19375.1.camel@ellerman.id.au>
Date:	Wed, 07 Oct 2015 20:13:30 +1100
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Segher Boessenkool <segher@...nel.crashing.org>
Cc:	Laura Abbott <labbott@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Missing operand for tlbie instruction on Power7

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.

cheers



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