linux-kernel - RE: [patch]pageattr: cache flush before tlb flush

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Date:	Tue, 19 Aug 2008 13:24:03 +0800
From:	"Li, Shaohua" <shaohua.li@...el.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Subject: RE: [patch]pageattr: cache flush before tlb flush



>-----Original Message-----
>From: H. Peter Anvin [mailto:hpa@...or.com]
>Sent: Tuesday, August 19, 2008 1:10 PM
>To: Li, Shaohua
>Cc: lkml; Andrew Morton; Ingo Molnar; Pallipadi, Venkatesh
>Subject: Re: [patch]pageattr: cache flush before tlb flush
>
>Shaohua Li wrote:
>> clflush uses a virtual address but cache line is physical indexed in
>> x86. In my understanding, clflush will do some pagetable walk, so doing
>> cache flush first should reduce some pagetable walk.
>>
>> Signed-off-by: Shaohua Li <shaohua.li@...el.com>
>
>I would say NAK on this.
>
>Doing the CLFLUSH first does cut down on page table walking, but opens a
>hole in the sequencing: first set PAT to an uncachable mode, then flush.
>
>If an unlucky prefetch comes in during this window, then you will have a
>dirty cache again.
>
>So no, this is not a good idea.
Ok, looks possible in theory.

Thanks,
Shaohua
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