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

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Message-ID: <54242F17.5010503@nexus-software.ie>
Date:	Thu, 25 Sep 2014 16:04:55 +0100
From:	Bryan O'Donoghue <pure.logic@...us-software.ie>
To:	Ingo Molnar <mingo@...nel.org>
CC:	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()

> It talks about:
>
> +       /*
> +        * Locate the page directory and flush the TLB.
> +        * On Quark X1000 rewriting CR3 flushes the TLB no if/else is required
> +        * to choose between __flush_tlb() and __flush_tlb_all()
> +        */
>          load_cr3(swapper_pg_dir);
>          __flush_tlb_all();
>
> But it is completely silent on the real reason for why we don't
> need a Quark quirk here, which would be something like:
>
> 	/*
> 	 * 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.
> 	 */
>
> Right?

OK.

IMO.

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.
  */

?
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