Subject: Re: Fix small race in 44x tlbie function

From: Hollis Blanchard <[email-masked]>
Date: Wed, 08 Aug 2007 17:11:09 -0500

On Wed, 2007-08-08 at 16:29 -0500, Josh Boyer wrote:
> On Wed, 8 Aug 2007 20:43:25 +0000 (UTC)
> Hollis Blanchard <[email-masked]> wrote:
> 
> > On Tue, 07 Aug 2007 14:20:50 +1000, David Gibson wrote:
> > > 
> > > This patch fixes the problem in both arch/ppc and arch/powerpc by
> > > inhibiting interrupts (even critical and debug interrupts) across the
> > > relevant instructions.
> > 
> > How could a critical or debug interrupt modify the contents of MMUCR?
> 
> Interrupts from UICs can be configured as critical.  If one of those
> triggers, (or any other CE triggers) and causes a tlb miss, you have a
> race.  The watchdog timer interrupt also is a CE IIRC.

By "causes a tlb miss", you mean the interrupt handler associated with
the critical-priority UIC interrupt performs MMIO which causes a TLB
miss? Regular code couldn't cause a TLB miss AFAICS, since the kernel is
always mapped, and an interrupt handler doesn't access userspace.

-- 
Hollis Blanchard
IBM Linux Technology Center