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

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Message-ID: <20080207191337.GA13111@elte.hu>
Date:	Thu, 7 Feb 2008 20:13:37 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	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


* Andi Kleen <andi@...stfloor.org> wrote:

> [probably stable material too]
> 
> Use global TLB flushes in MTRR code
> 
> Obviously kernel mappings should be flushed here too.

no, your patch is not needed:

>  	/* Flush all TLBs via a mov %cr3, %reg; mov %reg, %cr3 */
> -	__flush_tlb();
> +	__flush_tlb_all();

read the complete code:

        /*  Save value of CR4 and clear Page Global Enable (bit 7)  */
        if ( cpu_has_pge ) {
                cr4 = read_cr4();
                write_cr4(cr4 & ~X86_CR4_PGE);
        }

        /* Flush all TLBs via a mov %cr3, %reg; mov %reg, %cr3 */
        __flush_tlb();

first first turn off PGE and do a cr3 flush - that gets rid of all TLBs.

but even if it didnt get rid of it, the mirror image function, 
post_set(), we turn PGE back on in the cr4 _after_ we've flushed the 
TLBs via the cr3 - that will flush all TLBs again.

	Ingo
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