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Date:	Mon, 26 Mar 2007 01:08:42 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Hugh Dickins <hugh@...itas.com>, Zachary Amsden <zach@...are.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch -mm] i386: use pte_update_defer in
 ptep_test_and_clear_{dirty,young}

On Sun, 25 Mar 2007 23:37:08 -0700 (PDT) David Rientjes <rientjes@...gle.com> wrote:

> 	Date: Sun, 25 Mar 2007 23:07:43 -0800
> 	From: Zachary Amsden <zach@...are.com>
> 
> 	If you actually clear the bit, you need to:
> 
> 	+         pte_update_defer(vma->vm_mm, addr, ptep);
> 
> 	The reason is, when updating PTEs, the hypervisor must be notified.  Using
> 	atomic operations to do this is fine for all hypervisors I am aware of.
> 	However, for hypervisors which shadow page tables, if these PTE
> 	modifications are not trapped, you need a post-modification call to fulfill
> 	the update of the shadow page table.
> 
> Cc: Zachary Amsden <zach@...are.com>
> Cc: Hugh Dickins <hugh@...itas.com>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  include/asm-i386/pgtable.h |   26 ++++++++++++++------------
>  1 files changed, 14 insertions(+), 12 deletions(-)
> 
> diff --git a/include/asm-i386/pgtable.h b/include/asm-i386/pgtable.h
> --- a/include/asm-i386/pgtable.h
> +++ b/include/asm-i386/pgtable.h
> @@ -287,18 +287,24 @@ do {									\
>  static inline int ptep_test_and_clear_dirty(struct vm_area_struct *vma,
>  					    unsigned long addr, pte_t *ptep)
>  {
> -	if (!pte_dirty(*ptep))
> -		return 0;
> -	return test_and_clear_bit(_PAGE_BIT_DIRTY, &ptep->pte_low);
> +	int ret = 0;
> +	if (pte_dirty(*ptep))
> +		ret = test_and_clear_bit(_PAGE_BIT_DIRTY, &ptep->pte_low);
> +	if (ret)
> +		pte_update_defer(vma->vm_mm, addr, ptep);
> +	return ret;
>  }
>  

i386 allmodconfig:

include/asm/pgtable.h: In function 'ptep_test_and_clear_dirty':
include/asm/pgtable.h:294: error: dereferencing pointer to incomplete type
include/asm/pgtable.h: In function 'ptep_test_and_clear_young':
include/asm/pgtable.h:306: error: dereferencing pointer to incomplete type

Due to vm_area_struct.

Turning it into a stinky macro fixes it.


diff -puN include/asm-i386/pgtable.h~i386-use-pte_update_defer-in-ptep_test_and_clear_dirtyyoung-fix include/asm-i386/pgtable.h
--- a/include/asm-i386/pgtable.h~i386-use-pte_update_defer-in-ptep_test_and_clear_dirtyyoung-fix
+++ a/include/asm-i386/pgtable.h
@@ -284,28 +284,24 @@ do {									\
 } while (0)
 
 #define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_DIRTY
-static inline int ptep_test_and_clear_dirty(struct vm_area_struct *vma,
-					    unsigned long addr, pte_t *ptep)
-{
-	int ret = 0;
-	if (pte_dirty(*ptep))
-		ret = test_and_clear_bit(_PAGE_BIT_DIRTY, &ptep->pte_low);
-	if (ret)
-		pte_update_defer(vma->vm_mm, addr, ptep);
-	return ret;
-}
+#define ptep_test_and_clear_dirty(vma, addr, ptep) ({			\
+	int ret = 0;							\
+	if (pte_dirty(*ptep))						\
+		ret = test_and_clear_bit(_PAGE_BIT_DIRTY, &ptep->pte_low); \
+	if (ret)							\
+		pte_update_defer(vma->vm_mm, addr, ptep);		\
+	ret;								\
+})
 
 #define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
-static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
-					    unsigned long addr, pte_t *ptep)
-{
-	int ret = 0;
-	if (pte_young(*ptep))
-		ret = test_and_clear_bit(_PAGE_BIT_ACCESSED, &ptep->pte_low);
-	if (ret)
-		pte_update_defer(vma->vm_mm, addr, ptep);
-	return ret;
-}
+#define ptep_test_and_clear_young(vma, addr, ptep) ({			\
+	int ret = 0;							\
+	if (pte_young(*ptep))						\
+		ret = test_and_clear_bit(_PAGE_BIT_ACCESSED, &ptep->pte_low); \
+	if (ret)							\
+		pte_update_defer(vma->vm_mm, addr, ptep);		\
+	ret;								\
+})
 
 /*
  * Rules for using ptep_establish: the pte MUST be a user pte, and
_

-
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