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Subject: Re: Apparent kernel bug with GDB on ppc405
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reply-To: benh@kernel.crashing.org
To: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Cc: Daniel Jacobowitz <drow@false.org>, gdb@sourceware.org,         linuxppc-embedded@ozlabs.org, Matt Mackall <mpm@selenic.com>
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Date: Sat, 27 Oct 2007 01:36:00 -0000
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On Fri, 2007-10-26 at 15:41 -0500, Josh Boyer wrote:
> On Fri, 26 Oct 2007 11:51:22 +1000
> Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:
> 
> > 
> > On Wed, 2007-10-24 at 18:41 -0400, Daniel Jacobowitz wrote:
> > > On Wed, Oct 24, 2007 at 05:32:50PM -0500, Matt Mackall wrote:
> > > > Not completely implausible, but a) why isn't this seen on basically
> > > > every machine with software TLB? b) why does -local- GDB, which is
> > > > presumably doing much less work than gdbserver + network stack, not fail?
> > > 
> > > You said it yourself.  Local gdb does more work -> blows through more
> > > TLB entries.
> > > 
> > > I can't answer you about the other half, but I'm pretty sure TLB
> > > invalidation is already supposed to be happening... somewhere.
> > 
> > Yes. do_wp_page() -> ptep_clear_flush() -> flush_tlb_page()
> 
> Aren't there cases in do_wp_page that don't call ptep_clear_flush?
> Seems anonymous pages, and possibly shared writeable pages skip that
> step if reuse is true.

Nah, if that was broken, everybody would be in bad shape. I think I know
what's up, see my other email.

Cheers,
Ben.