linux-kernel - Re: [patch 0/7] x86, cpa: cpa related changes to be inline with TLB Application note

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Date:	Sun, 14 Sep 2008 17:29:47 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	hpa@...or.com, tglx@...utronix.de, arjan@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 0/7] x86, cpa: cpa related changes to be inline with
	TLB Application note


* Suresh Siddha <suresh.b.siddha@...el.com> wrote:

> TLB Application note[1] says:
> 	
> "The TLBs may contain both ordinary and large-page translations for a 4-KByte
>  range of linear addresses. This may occur if software modifies the paging
>  structures so that the page size used for the address range changes. If the
>  two translations differ with respect to page frame or attributes (e.g.,
>  permissions), processor behavior is undefined and may be implementation 
>  specific. The processor may use a page frame or attributes that correspond to
>  neither translation; it may improperly set or fail to set the dirty bit in the
>  appropriate paging-structure entry.
>  
>  Such undefined behavior is problematic because prefetches and memory accesses
>  that are a result of speculative execution may occur, using the affected range
>  of linear addresses. It is also problematic if software (including the software
>  modifying the paging structures) is accessing data or executing code in the
>  affected range of linear addresses. Software should not write to a
>  paging-structure entry in a way that would change, for any linear address,
>  both the page size and either the page frame or attributes."
> 
> Currently we violate this at:
> 
> a. kernel identity mapping, where large/small pages setup very early in the
>    boot will be split up/merged into large pages along with attribute changes
>    during the direct memory mapping init.
> 
> b. while doing cpa(), potentially we will split large page and change attribute
>    both at the same time.
> 
> Following patches fixes this behavior.
> 
> [1] http://developer.intel.com/design/processor/applnots/317080.pdf
> 
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>

applied to tip/x86/pat, thanks Suresh.

	Ingo
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