linux-kernel - Re: BUG: about flush TLB during unmapping a page in memory subsystem

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Date:	Fri, 20 Oct 2006 15:54:27 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	yunfeng zhang <zyf.zeroos@...il.com>
Cc:	David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org
Subject: Re: BUG: about flush TLB during unmapping a page in memory
	subsystem

On Fri, 2006-10-20 at 13:10 +0800, yunfeng zhang wrote:
> Maybe, the solution is below
> 
> ...
> // >>> ptep_clear((__vma)->vm_mm, __address, __ptep);
> // >>> flush_tlb_page(__vma, __address);
> // >>> __ptep;
> ...
> 
> And even so, we also get a pte with present = 0 AND its dirty = 1, an odd pte.
> 
> Remember B dirtied the pte before A executes flush_tlb_page.

It's very much architecture specific. I suppose x86 must have some HW
requirements of checking if the PTE is still present atomically when
setting the dirty bit but I can't tell for sure :)

On PowerPC, we don't use HW dirty bits, we use SW for that, thus the
ptep_get_and_clear will be enough to prevent any further dirty bit to be
set.

Ben.


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