linux-kernel - Re: [PATCH] x86: Quark: Flush TLB via CR3 not CR4.PGE in setup

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Date:	Thu, 25 Sep 2014 20:28:14 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	Bryan O'Donoghue <pure.logic@...us-software.ie>, hpa@...or.com,
	mingo@...hat.com, tglx@...utronix.de, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Quark: Flush TLB via CR3 not CR4.PGE in setup_arch()


* Henrique de Moraes Holschuh <hmh@....eng.br> wrote:

> On Thu, 25 Sep 2014, Ingo Molnar wrote:
> > > If we're adding a comment though the first thing the comment ought to say is
> > > what the code does for everybody else - stuff CR3 and flush the TLB, then it
> > > should comment on the exception for Quark.
> > > 
> > > /*
> > >  * Locate the page directory and flush the TLB.
> > >  *
> > >  * On Quark CPUs we still have the PGE bit set so
> > >  * __flush_tlb_all() is not yet doing what it says - but
> > >  * accidentally we have a cr3 flush here which is what is
> > >  * needed - so there's no need to add a Quark quirk here.
> > >  */
> > > 
> > > ?
> > 
> > Yeah, fair enough. You can even put the latter in parentheses, to 
> > signal that it's all a rare case.
> 
> I'd have mentioned "erratum" there, otherwise people won't understand why
> the PGE bit being set would be a problem in the first place.
> 
> Something like:
> 
> /*
>  * Locate the page directory and flush the TLB.
>  *
>  * On Quark X1000 CPUs we still have the PGE bit incorrectly set
>  * due to a processor erratum, so __flush_tlb_all() is not yet
>  * doing what it says.  Fortunately we have a cr3 flush here,
>  * which is what is needed in this processor to flush TLBs, so
>  * there's no need to add a Quark X1000 quirk here.
>  */

Yeah.

I'd also add the fact that it's an unintended erratum to the 
Quark quirk section of early_init_intel() as well.

Thanks,

	Ingo
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