Subject: Re: [PATCH 12/15] powerpc/book3e: Use way 3 for linear mapping bolted entry

From: Benjamin Herrenschmidt <[email-masked]>
Date: Tue, 19 Apr 2011 07:40:34 +1000

On Mon, 2011-04-18 at 07:43 -0500, Kumar Gala wrote:
> On Apr 15, 2011, at 3:32 AM, Michael Ellerman wrote:
> 
> > From: Benjamin Herrenschmidt <[email-masked]>
> > 
> > An erratum on A2 can lead to the bolted entry we insert for the linear
> > mapping being evicted, to avoid that write the bolted entry to way 3.
> > 
> > Signed-off-by: Benjamin Herrenschmidt <[email-masked]>
> > Signed-off-by: Michael Ellerman <[email-masked]>
> > ---
> > arch/powerpc/kernel/exceptions-64e.S |    5 +++--
> > 1 files changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
> > index 5c43063..e6c0926 100644
> > --- a/arch/powerpc/kernel/exceptions-64e.S
> > +++ b/arch/powerpc/kernel/exceptions-64e.S
> > @@ -864,8 +864,9 @@ have_hes:
> > 	 * that will have to be made dependent on whether we are running under
> > 	 * a hypervisor I suppose.
> > 	 */
> > -	ori	r3,r3,MAS0_HES | MAS0_WQ_ALLWAYS
> > -	mtspr	SPRN_MAS0,r3
> > +	ori	r11,r3,MAS0_WQ_ALLWAYS
> > +	oris	r11,r11,MAS0_ESEL(3)@h /* Use way 3: workaround A2 erratum 376 */
> > +	mtspr	SPRN_MAS0,r11
> > 	lis	r3,(MAS1_VALID | MAS1_IPROT)@h
> > 	ori	r3,r3,BOOK3E_PAGESZ_1GB << MAS1_TSIZE_SHIFT
> > 	mtspr	SPRN_MAS1,r3
> 
> Seems like this should have a MMU Feature bit or something for A2.

Too early. We haven't detected the CPU and are establishing the initial
TLB entry here.

Any reason why that wouldn't work on something else anyways ?

Cheers,
Ben.