linux-kernel - Re: [PATCH] Use global TLB flushes in MTRR code

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Message-ID: <20080208114419.GB4745@one.firstfloor.org>
Date:	Fri, 8 Feb 2008 12:44:19 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andi Kleen <andi@...stfloor.org>, davej@...emonkey.org.uk,
	tglx@...utronix.de, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] Use global TLB flushes in MTRR code

> because it's not just an open-coded __tlb_flush_all(), it _disables PGE 
> and keeps it so while the MTRR's are changed on all CPUs_.

Yes and? 

> 
> Your patch adds __flush_tlb_all() which re-enables the PGE bit in cr4, 
> see asm-x86/tlbflush.h:
> 
>         /* clear PGE */
>         write_cr4(cr4 & ~X86_CR4_PGE);
>         /* write old PGE again and flush TLBs */
>         write_cr4(cr4);
> 
> so we'll keep PGE enabled during the MTRR setting - which changes 
> behavior.

It changes behaviour in some minor ways but I don't think it makes any 
difference. PGE only influences TLB flushes (according to its 
specification) and all the TLB flushes still run with PGE disabled.

-Andi

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