linux-kernel - [ 067/117] um: Implement a custom pte

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Message-Id: <20120528031212.118966848@decadent.org.uk>
Date:	Mon, 28 May 2012 04:13:09 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Richard Weinberger <richard@....at>
Subject: [ 067/117] um: Implement a custom pte_same() function

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Richard Weinberger <richard@....at>

commit f15b9000eb1d09bbaa4b0a6b2089d7e1f64e84b3 upstream.

UML uses the _PAGE_NEWPAGE flag to mark pages which are not jet
installed on the host side using mmap().
pte_same() has to ignore this flag, otherwise unuse_pte_range()
is unable to unuse the page because two identical
page tables entries with different _PAGE_NEWPAGE flags would not
match and swapoff() would never return.

Analyzed-by: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Richard Weinberger <richard@....at>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/um/include/asm/pgtable.h |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/um/include/asm/pgtable.h b/arch/um/include/asm/pgtable.h
index 6a3f984..294254e 100644
--- a/arch/um/include/asm/pgtable.h
+++ b/arch/um/include/asm/pgtable.h
@@ -273,6 +273,12 @@ static inline void set_pte(pte_t *pteptr, pte_t pteval)
 }
 #define set_pte_at(mm,addr,ptep,pteval) set_pte(ptep,pteval)
 
+#define __HAVE_ARCH_PTE_SAME
+static inline int pte_same(pte_t pte_a, pte_t pte_b)
+{
+	return !((pte_val(pte_a) ^ pte_val(pte_b)) & ~_PAGE_NEWPAGE);
+}
+
 /*
  * Conversion functions: convert a page and protection to a page entry,
  * and a page entry and page directory to the page they refer to.


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