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Date: Thu, 27 Apr 2006 10:00:34 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Zachary Amsden <zach@vmware.com>
CC: Andrew Morton <akpm@osdl.com>, Linux-Kernel <linux-kernel@vger.kernel.org>,
       Hugh Dickins <hugh@veritas.com>, Jan Beulich <jbeulich@novell.com>,
       Keir Fraser <Keir.Fraser@cl.cam.ac.uk>,
       Pratap Subrahmanyam <pratap@vmware.com>
Subject: Re: [PATCH 2/2] I386 convert pae wmb to non smp
References: <200604262203.k3QM3qOC009581@zach-dev.vmware.com>
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Zachary Amsden wrote:

>Similar to the last bug, on set_pte, we don't want the compiler to re-order
>the write of the PTE, even in non-SMP configurations, since if the write of
>the low word occurs first, the TLB could prefetch a bad highmem mapping which
>has been aliased into low memory.
>

wmb() means that it also orders IO memory. It is no difference for
i386, but smp_wmb() actually has the right semantics of the abstract
Linux memory model.

>Signed-off-by: Zachary Amsden <zach@vmware.com>
>
>Index: linux-2.6.17-rc/include/asm-i386/pgtable-3level.h
>===================================================================
>--- linux-2.6.17-rc.orig/include/asm-i386/pgtable-3level.h	2006-04-26 08:38:57.000000000 -0700
>+++ linux-2.6.17-rc/include/asm-i386/pgtable-3level.h	2006-04-26 14:45:12.000000000 -0700
>@@ -53,7 +53,7 @@ static inline int pte_exec_kernel(pte_t 
> static inline void set_pte(pte_t *ptep, pte_t pte)
> {
> 	ptep->pte_high = pte.pte_high;
>-	smp_wmb();
>+	wmb();
> 	ptep->pte_low = pte.pte_low;
> }
> #define set_pte_at(mm,addr,ptep,pteval) set_pte(ptep,pteval)
>
>  
>

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