linux/x86: Adjust and fix page table handling.

Ensure that all and only those page table entries that have their
present bit set undergo p2m/m2p translation in all relevant places.
This should fix migration issues with _PAGE_PROTNONE pages which
previously could retain MFNs in PTEs while having the present bit
clear (and thus were not getting (un)canonicalized during save/
restore).

Many thanks to Keir Fraser for his analysis, suggestions, and
corrections.

Signed-off-by: Jan Beulich <jbeulich@novell.com>

diff --git a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/maddr.h b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/maddr.h
index f805d6ea602279cb96e7443967ac23d672f68cc2..1d345898cc5ec750f0dc4605800d4a510f9f081c 100644 (file)
--- a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/maddr.h
+++ b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/maddr.h
@@ -21,6 +21,7 @@ typedef unsigned long maddr_t;
 #ifdef CONFIG_XEN
 
 extern unsigned long *phys_to_machine_mapping;
+extern unsigned long  max_mapnr;
 
 #undef machine_to_phys_mapping
 extern unsigned long *machine_to_phys_mapping;
@@ -30,20 +31,20 @@ static inline unsigned long pfn_to_mfn(unsigned long pfn)
 {
        if (xen_feature(XENFEAT_auto_translated_physmap))
                return pfn;
-       return phys_to_machine_mapping[(unsigned int)(pfn)] &
-               ~FOREIGN_FRAME_BIT;
+       BUG_ON(max_mapnr && pfn >= max_mapnr);
+       return phys_to_machine_mapping[pfn] & ~FOREIGN_FRAME_BIT;
 }
 
 static inline int phys_to_machine_mapping_valid(unsigned long pfn)
 {
        if (xen_feature(XENFEAT_auto_translated_physmap))
                return 1;
+       BUG_ON(max_mapnr && pfn >= max_mapnr);
        return (phys_to_machine_mapping[pfn] != INVALID_P2M_ENTRY);
 }
 
 static inline unsigned long mfn_to_pfn(unsigned long mfn)
 {
-       extern unsigned long max_mapnr;
        unsigned long pfn;
 
        if (xen_feature(XENFEAT_auto_translated_physmap))
@@ -92,7 +93,6 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
  */
 static inline unsigned long mfn_to_local_pfn(unsigned long mfn)
 {
-       extern unsigned long max_mapnr;
        unsigned long pfn = mfn_to_pfn(mfn);
        if ((pfn < max_mapnr)
            && !xen_feature(XENFEAT_auto_translated_physmap)
@@ -103,6 +103,7 @@ static inline unsigned long mfn_to_local_pfn(unsigned long mfn)
 
 static inline void set_phys_to_machine(unsigned long pfn, unsigned long mfn)
 {
+       BUG_ON(pfn >= max_mapnr);
        if (xen_feature(XENFEAT_auto_translated_physmap)) {
                BUG_ON(pfn != mfn && mfn != INVALID_P2M_ENTRY);
                return;
@@ -124,6 +125,20 @@ static inline paddr_t machine_to_phys(maddr_t machine)
        return phys;
 }
 
+#ifdef CONFIG_X86_PAE
+static inline paddr_t pte_phys_to_machine(paddr_t phys)
+{
+       /*
+        * In PAE mode, the NX bit needs to be dealt with in the value
+        * passed to pfn_to_mfn(). On x86_64, we need to mask it off,
+        * but for i386 the conversion to ulong for the argument will
+        * clip it off.
+        */
+       maddr_t machine = pfn_to_mfn(phys >> PAGE_SHIFT);
+       machine = (machine << PAGE_SHIFT) | (phys & ~PHYSICAL_PAGE_MASK);
+       return machine;
+}
+
 static inline paddr_t pte_machine_to_phys(maddr_t machine)
 {
        /*
@@ -136,6 +151,7 @@ static inline paddr_t pte_machine_to_phys(maddr_t machine)
        phys = (phys << PAGE_SHIFT) | (machine & ~PHYSICAL_PAGE_MASK);
        return phys;
 }
+#endif
 
 #else /* !CONFIG_XEN */
 
@@ -146,7 +162,6 @@ static inline paddr_t pte_machine_to_phys(maddr_t machine)
 #define phys_to_machine_mapping_valid(pfn) (1)
 #define phys_to_machine(phys) ((maddr_t)(phys))
 #define machine_to_phys(mach) ((paddr_t)(mach))
-#define pte_machine_to_phys(mach) ((paddr_t)(mach))
 
 #endif /* !CONFIG_XEN */
 

diff --git a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/page.h b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/page.h
index 1525dbfca4323a9fbf5596d16bf5dc8fa4cc31bc..7edb3e7ccfe25c9695b4761719b3f0e585ed883a 100644 (file)
--- a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/page.h
+++ b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/page.h
@@ -29,6 +29,13 @@
 #include <xen/interface/xen.h>
 #include <xen/features.h>
 
+/*
+ * Need to repeat this here in order to not include pgtable.h (which in turn
+ * depends on definitions made here), but to be able to use the symbolic
+ * below. The preprocessor will warn if the two definitions aren't identical.
+ */
+#define _PAGE_PRESENT  0x001
+
 #define arch_free_page(_page,_order)           \
 ({     int foreign = PageForeign(_page);       \
        if (foreign)                            \
@@ -81,40 +88,38 @@ typedef struct { unsigned long long pgprot; } pgprot_t;
 #define pgprot_val(x)  ((x).pgprot)
 #include <asm/maddr.h>
 #define __pte(x) ({ unsigned long long _x = (x);        \
-    if (_x & 1) _x = phys_to_machine(_x);               \
+    if (_x & _PAGE_PRESENT) _x = pte_phys_to_machine(_x);   \
     ((pte_t) {(unsigned long)(_x), (unsigned long)(_x>>32)}); })
 #define __pgd(x) ({ unsigned long long _x = (x); \
-    (((_x)&1) ? ((pgd_t) {phys_to_machine(_x)}) : ((pgd_t) {(_x)})); })
+    (pgd_t) {((_x) & _PAGE_PRESENT) ? pte_phys_to_machine(_x) : (_x)}; })
 #define __pmd(x) ({ unsigned long long _x = (x); \
-    (((_x)&1) ? ((pmd_t) {phys_to_machine(_x)}) : ((pmd_t) {(_x)})); })
+    (pmd_t) {((_x) & _PAGE_PRESENT) ? pte_phys_to_machine(_x) : (_x)}; })
+static inline unsigned long long pte_val_ma(pte_t x)
+{
+       return ((unsigned long long)x.pte_high << 32) | x.pte_low;
+}
 static inline unsigned long long pte_val(pte_t x)
 {
-       unsigned long long ret;
-
-       if (x.pte_low) {
-               ret = x.pte_low | (unsigned long long)x.pte_high << 32;
-               ret = pte_machine_to_phys(ret) | 1;
-       } else {
-               ret = 0;
-       }
+       unsigned long long ret = pte_val_ma(x);
+       if (x.pte_low & _PAGE_PRESENT) ret = pte_machine_to_phys(ret);
        return ret;
 }
 static inline unsigned long long pmd_val(pmd_t x)
 {
        unsigned long long ret = x.pmd;
-       if (ret) ret = pte_machine_to_phys(ret) | 1;
+#ifdef CONFIG_XEN_COMPAT_030002
+       if (ret) ret = pte_machine_to_phys(ret) | _PAGE_PRESENT;
+#else
+       if (ret & _PAGE_PRESENT) ret = pte_machine_to_phys(ret);
+#endif
        return ret;
 }
 static inline unsigned long long pgd_val(pgd_t x)
 {
        unsigned long long ret = x.pgd;
-       if (ret) ret = pte_machine_to_phys(ret) | 1;
+       if (ret & _PAGE_PRESENT) ret = pte_machine_to_phys(ret);
        return ret;
 }
-static inline unsigned long long pte_val_ma(pte_t x)
-{
-       return (unsigned long long)x.pte_high << 32 | x.pte_low;
-}
 #define HPAGE_SHIFT    21
 #else
 typedef struct { unsigned long pte_low; } pte_t;
@@ -123,23 +128,23 @@ typedef struct { unsigned long pgprot; } pgprot_t;
 #define pgprot_val(x)  ((x).pgprot)
 #include <asm/maddr.h>
 #define boot_pte_t pte_t /* or would you rather have a typedef */
-#define pte_val(x)     (((x).pte_low & 1) ? \
-                        pte_machine_to_phys((x).pte_low) : \
+#define pte_val(x)     (((x).pte_low & _PAGE_PRESENT) ? \
+                        machine_to_phys((x).pte_low) : \
                         (x).pte_low)
 #define pte_val_ma(x)  ((x).pte_low)
 #define __pte(x) ({ unsigned long _x = (x); \
-    (((_x)&1) ? ((pte_t) {phys_to_machine(_x)}) : ((pte_t) {(_x)})); })
+    (pte_t) {((_x) & _PAGE_PRESENT) ? phys_to_machine(_x) : (_x)}; })
 #define __pgd(x) ({ unsigned long _x = (x); \
-    (((_x)&1) ? ((pgd_t) {phys_to_machine(_x)}) : ((pgd_t) {(_x)})); })
+    (pgd_t) {((_x) & _PAGE_PRESENT) ? phys_to_machine(_x) : (_x)}; })
 static inline unsigned long pgd_val(pgd_t x)
 {
        unsigned long ret = x.pgd;
-       if (ret) ret = pte_machine_to_phys(ret) | 1;
+       if (ret & _PAGE_PRESENT) ret = machine_to_phys(ret);
        return ret;
 }
 #define HPAGE_SHIFT    22
 #endif
-#define PTE_MASK       PAGE_MASK
+#define PTE_MASK       PHYSICAL_PAGE_MASK
 
 #ifdef CONFIG_HUGETLB_PAGE
 #define HPAGE_SIZE     ((1UL) << HPAGE_SHIFT)

diff --git a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/pgtable-2level.h b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/pgtable-2level.h
index 34cb67f06fe9870822df8826a3f01800ffe70169..f7250a35975673c6fc68aaf3f88ce4c2f1c42936 100644 (file)
--- a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/pgtable-2level.h
+++ b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/pgtable-2level.h
@@ -38,8 +38,11 @@
 
 #define ptep_get_and_clear(mm,addr,xp) __pte_ma(xchg(&(xp)->pte_low, 0))
 #define pte_same(a, b)         ((a).pte_low == (b).pte_low)
-#define pte_mfn(_pte) ((_pte).pte_low >> PAGE_SHIFT)
-#define pte_pfn(_pte) mfn_to_local_pfn(pte_mfn(_pte))
+#define __pte_mfn(_pte) ((_pte).pte_low >> PAGE_SHIFT)
+#define pte_mfn(_pte) ((_pte).pte_low & _PAGE_PRESENT ? \
+       __pte_mfn(_pte) : pfn_to_mfn(__pte_mfn(_pte)))
+#define pte_pfn(_pte) ((_pte).pte_low & _PAGE_PRESENT ? \
+       mfn_to_local_pfn(__pte_mfn(_pte)) : __pte_mfn(_pte))
 
 #define pte_page(_pte) pfn_to_page(pte_pfn(_pte))
 

diff --git a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/pgtable-3level.h b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/pgtable-3level.h
index 29b4036a72ba4903c578214817a5df45a628b82d..7acdccc4849f22738d48c597701e384f72ceef5b 100644 (file)
--- a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/pgtable-3level.h
+++ b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/pgtable-3level.h
@@ -145,21 +145,24 @@ static inline int pte_none(pte_t pte)
        return !pte.pte_low && !pte.pte_high;
 }
 
-#define pte_mfn(_pte) (((_pte).pte_low >> PAGE_SHIFT) |\
-                      (((_pte).pte_high & 0xfff) << (32-PAGE_SHIFT)))
-#define pte_pfn(_pte) mfn_to_local_pfn(pte_mfn(_pte))
+#define __pte_mfn(_pte) (((_pte).pte_low >> PAGE_SHIFT) | \
+                        ((_pte).pte_high << (32-PAGE_SHIFT)))
+#define pte_mfn(_pte) ((_pte).pte_low & _PAGE_PRESENT ? \
+       __pte_mfn(_pte) : pfn_to_mfn(__pte_mfn(_pte)))
+#define pte_pfn(_pte) ((_pte).pte_low & _PAGE_PRESENT ? \
+       mfn_to_local_pfn(__pte_mfn(_pte)) : __pte_mfn(_pte))
 
 extern unsigned long long __supported_pte_mask;
 
 static inline pte_t pfn_pte(unsigned long page_nr, pgprot_t pgprot)
 {
-       return pfn_pte_ma(pfn_to_mfn(page_nr), pgprot);
+       return __pte((((unsigned long long)page_nr << PAGE_SHIFT) |
+                       pgprot_val(pgprot)) & __supported_pte_mask);
 }
 
 static inline pmd_t pfn_pmd(unsigned long page_nr, pgprot_t pgprot)
 {
-       BUG(); panic("needs review");
-       return __pmd((((unsigned long long)page_nr << PAGE_SHIFT) | \
+       return __pmd((((unsigned long long)page_nr << PAGE_SHIFT) |
                        pgprot_val(pgprot)) & __supported_pte_mask);
 }
 

diff --git a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/pgtable.h b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/pgtable.h
index 732dfa7df2503ac0e233a83e8e3cd68685b93bff..5be42a9de5406a6315e48b0858934f8d147a4ca2 100644 (file)
--- a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/pgtable.h
+++ b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/pgtable.h
@@ -315,18 +315,19 @@ static inline void clone_pgd_range(pgd_t *dst, pgd_t *src, int count)
 
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
-       pte.pte_low &= _PAGE_CHG_MASK;
-       pte.pte_low |= pgprot_val(newprot);
-#ifdef CONFIG_X86_PAE
        /*
-        * Chop off the NX bit (if present), and add the NX portion of
-        * the newprot (if present):
+        * Since this might change the present bit (which controls whether
+        * a pte_t object has undergone p2m translation), we must use
+        * pte_val() on the input pte and __pte() for the return value.
         */
-       pte.pte_high &= ~(1 << (_PAGE_BIT_NX - 32));
-       pte.pte_high |= (pgprot_val(newprot) >> 32) & \
-                                       (__supported_pte_mask >> 32);
+       paddr_t pteval = pte_val(pte);
+
+       pteval &= _PAGE_CHG_MASK;
+       pteval |= pgprot_val(newprot);
+#ifdef CONFIG_X86_PAE
+       pteval &= __supported_pte_mask;
 #endif
-       return pte;
+       return __pte(pteval);
 }
 
 #define pmd_large(pmd) \

diff --git a/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/maddr.h b/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/maddr.h
index 77544b3ca2c62b1532c3b68397eb8820dc077d14..249b95965f91f83c3cd369a1f02755296f321dd0 100644 (file)
--- a/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/maddr.h
+++ b/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/maddr.h
@@ -25,14 +25,15 @@ static inline unsigned long pfn_to_mfn(unsigned long pfn)
 {
        if (xen_feature(XENFEAT_auto_translated_physmap))
                return pfn;
-       return phys_to_machine_mapping[(unsigned int)(pfn)] &
-               ~FOREIGN_FRAME_BIT;
+       BUG_ON(end_pfn && pfn >= end_pfn);
+       return phys_to_machine_mapping[pfn] & ~FOREIGN_FRAME_BIT;
 }
 
 static inline int phys_to_machine_mapping_valid(unsigned long pfn)
 {
        if (xen_feature(XENFEAT_auto_translated_physmap))
                return 1;
+       BUG_ON(end_pfn && pfn >= end_pfn);
        return (phys_to_machine_mapping[pfn] != INVALID_P2M_ENTRY);
 }
 
@@ -96,6 +97,7 @@ static inline unsigned long mfn_to_local_pfn(unsigned long mfn)
 
 static inline void set_phys_to_machine(unsigned long pfn, unsigned long mfn)
 {
+       BUG_ON(pfn >= end_pfn);
        if (xen_feature(XENFEAT_auto_translated_physmap)) {
                BUG_ON(pfn != mfn && mfn != INVALID_P2M_ENTRY);
                return;
@@ -117,6 +119,14 @@ static inline paddr_t machine_to_phys(maddr_t machine)
        return phys;
 }
 
+static inline paddr_t pte_phys_to_machine(paddr_t phys)
+{
+       maddr_t machine;
+       machine = pfn_to_mfn((phys & PHYSICAL_PAGE_MASK) >> PAGE_SHIFT);
+       machine = (machine << PAGE_SHIFT) | (phys & ~PHYSICAL_PAGE_MASK);
+       return machine;
+}
+
 static inline paddr_t pte_machine_to_phys(maddr_t machine)
 {
        paddr_t phys;
@@ -134,7 +144,6 @@ static inline paddr_t pte_machine_to_phys(maddr_t machine)
 #define phys_to_machine_mapping_valid(pfn) (1)
 #define phys_to_machine(phys) ((maddr_t)(phys))
 #define machine_to_phys(mach) ((paddr_t)(mach))
-#define pte_machine_to_phys(mach) ((paddr_t)(mach))
 
 #endif /* !CONFIG_XEN */
 

diff --git a/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/page.h b/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/page.h
index 8c8e02131679c4aae060b5d4bef629271c58bfc4..6340e6e6d61c17488bbc47d281dc556909676747 100644 (file)
--- a/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/page.h
+++ b/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/page.h
@@ -9,6 +9,13 @@
 #endif
 #include <xen/interface/xen.h> 
 
+/*
+ * Need to repeat this here in order to not include pgtable.h (which in turn
+ * depends on definitions made here), but to be able to use the symbolic
+ * below. The preprocessor will warn if the two definitions aren't identical.
+ */
+#define _PAGE_PRESENT  0x001
+
 #define arch_free_page(_page,_order)           \
 ({     int foreign = PageForeign(_page);       \
        if (foreign)                            \
@@ -95,28 +102,33 @@ typedef struct { unsigned long pgd; } pgd_t;
 
 typedef struct { unsigned long pgprot; } pgprot_t;
 
-#define pte_val(x)     (((x).pte & 1) ? pte_machine_to_phys((x).pte) : \
+#define pte_val(x)     (((x).pte & _PAGE_PRESENT) ? \
+                        pte_machine_to_phys((x).pte) : \
                         (x).pte)
 #define pte_val_ma(x)  ((x).pte)
 
 static inline unsigned long pmd_val(pmd_t x)
 {
        unsigned long ret = x.pmd;
-       if (ret) ret = pte_machine_to_phys(ret);
+#ifdef CONFIG_XEN_COMPAT_030002
+       if (ret) ret = pte_machine_to_phys(ret) | _PAGE_PRESENT;
+#else
+       if (ret & _PAGE_PRESENT) ret = pte_machine_to_phys(ret);
+#endif
        return ret;
 }
 
 static inline unsigned long pud_val(pud_t x)
 {
        unsigned long ret = x.pud;
-       if (ret) ret = pte_machine_to_phys(ret);
+       if (ret & _PAGE_PRESENT) ret = pte_machine_to_phys(ret);
        return ret;
 }
 
 static inline unsigned long pgd_val(pgd_t x)
 {
        unsigned long ret = x.pgd;
-       if (ret) ret = pte_machine_to_phys(ret);
+       if (ret & _PAGE_PRESENT) ret = pte_machine_to_phys(ret);
        return ret;
 }
 
@@ -124,25 +136,25 @@ static inline unsigned long pgd_val(pgd_t x)
 
 static inline pte_t __pte(unsigned long x)
 {
-       if (x & 1) x = phys_to_machine(x);
+       if (x & _PAGE_PRESENT) x = pte_phys_to_machine(x);
        return ((pte_t) { (x) });
 }
 
 static inline pmd_t __pmd(unsigned long x)
 {
-       if ((x & 1)) x = phys_to_machine(x);
+       if (x & _PAGE_PRESENT) x = pte_phys_to_machine(x);
        return ((pmd_t) { (x) });
 }
 
 static inline pud_t __pud(unsigned long x)
 {
-       if ((x & 1)) x = phys_to_machine(x);
+       if (x & _PAGE_PRESENT) x = pte_phys_to_machine(x);
        return ((pud_t) { (x) });
 }
 
 static inline pgd_t __pgd(unsigned long x)
 {
-       if ((x & 1)) x = phys_to_machine(x);
+       if (x & _PAGE_PRESENT) x = pte_phys_to_machine(x);
        return ((pgd_t) { (x) });
 }
 

diff --git a/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/pgtable.h b/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/pgtable.h
index b3dd8f2b2f816356b66f6c13d39a89decaf1564c..5aa07770efc0593f585d08971f7a5840dbf007ff 100644 (file)
--- a/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/pgtable.h
+++ b/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/pgtable.h
@@ -302,19 +302,20 @@ static inline unsigned long pud_bad(pud_t pud)
 
 #define pages_to_mb(x) ((x) >> (20-PAGE_SHIFT))
 
-#define pte_mfn(_pte) (((_pte).pte & PTE_MASK) >> PAGE_SHIFT)
-#define pte_pfn(_pte) mfn_to_local_pfn(pte_mfn(_pte))
+#define __pte_mfn(_pte) (((_pte).pte & PTE_MASK) >> PAGE_SHIFT)
+#define pte_mfn(_pte) ((_pte).pte & _PAGE_PRESENT ? \
+       __pte_mfn(_pte) : pfn_to_mfn(__pte_mfn(_pte)))
+#define pte_pfn(_pte) ((_pte).pte & _PAGE_PRESENT ? \
+       mfn_to_local_pfn(__pte_mfn(_pte)) : __pte_mfn(_pte))
 
 #define pte_page(x)    pfn_to_page(pte_pfn(x))
 
 static inline pte_t pfn_pte(unsigned long page_nr, pgprot_t pgprot)
 {
-       pte_t pte;
-        
-       (pte).pte = (pfn_to_mfn(page_nr) << PAGE_SHIFT);
-       (pte).pte |= pgprot_val(pgprot);
-       (pte).pte &= __supported_pte_mask;
-       return pte;
+       unsigned long pte = page_nr << PAGE_SHIFT;
+       pte |= pgprot_val(pgprot);
+       pte &= __supported_pte_mask;
+       return __pte(pte);
 }
 
 /*
@@ -446,18 +447,25 @@ static inline pud_t *pud_offset_k(pgd_t *pgd, unsigned long address)
 /* physical address -> PTE */
 static inline pte_t mk_pte_phys(unsigned long physpage, pgprot_t pgprot)
 { 
-       pte_t pte;
-       (pte).pte = physpage | pgprot_val(pgprot); 
-       return pte; 
+       unsigned long pteval;
+       pteval = physpage | pgprot_val(pgprot);
+       return __pte(pteval);
 }
  
 /* Change flags of a PTE */
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 { 
-        (pte).pte &= _PAGE_CHG_MASK;
-       (pte).pte |= pgprot_val(newprot);
-       (pte).pte &= __supported_pte_mask;
-       return pte; 
+       /*
+        * Since this might change the present bit (which controls whether
+        * a pte_t object has undergone p2m translation), we must use
+        * pte_val() on the input pte and __pte() for the return value.
+        */
+       unsigned long pteval = pte_val(pte);
+
+       pteval &= _PAGE_CHG_MASK;
+       pteval |= pgprot_val(newprot);
+       pteval &= __supported_pte_mask;
+       return __pte(pteval);
 }
 
 #define pte_index(address) \