Index: head-2006-06-07/arch/i386/mm/pgtable-xen.c
===================================================================
--- head-2006-06-07.orig/arch/i386/mm/pgtable-xen.c	2006-06-08 12:41:06.000000000 +0200
+++ head-2006-06-07/arch/i386/mm/pgtable-xen.c	2006-06-08 12:41:33.000000000 +0200
@@ -614,6 +614,12 @@ void mm_pin_all(void)
 	}
 }
 
+void _arch_dup_mmap(struct mm_struct *mm)
+{
+	if (!test_bit(PG_pinned, &virt_to_page(mm->pgd)->flags))
+		mm_pin(mm);
+}
+
 void _arch_exit_mmap(struct mm_struct *mm)
 {
 	struct task_struct *tsk = current;
Index: head-2006-06-07/arch/x86_64/mm/pageattr-xen.c
===================================================================
--- head-2006-06-07.orig/arch/x86_64/mm/pageattr-xen.c	2006-06-08 12:41:06.000000000 +0200
+++ head-2006-06-07/arch/x86_64/mm/pageattr-xen.c	2006-06-08 12:41:33.000000000 +0200
@@ -130,6 +130,12 @@ void mm_pin_all(void)
 				  context.unpinned));
 }
 
+void _arch_dup_mmap(struct mm_struct *mm)
+{
+    if (!mm->context.pinned)
+        mm_pin(mm);
+}
+
 void _arch_exit_mmap(struct mm_struct *mm)
 {
     struct task_struct *tsk = current;
Index: head-2006-06-07/include/asm-i386/mach-xen/asm/mmu.h
===================================================================
--- head-2006-06-07.orig/include/asm-i386/mach-xen/asm/mmu.h	2006-06-08 12:41:06.000000000 +0200
+++ head-2006-06-07/include/asm-i386/mach-xen/asm/mmu.h	2006-06-08 12:41:33.000000000 +0200
@@ -18,4 +18,8 @@ typedef struct { 
 extern void _arch_exit_mmap(struct mm_struct *mm);
 #define arch_exit_mmap(_mm) _arch_exit_mmap(_mm)
 
+/* kernel/fork.c:dup_mmap hook */
+extern void _arch_dup_mmap(struct mm_struct *mm);
+#define arch_dup_mmap(mm, oldmm) ((void)(oldmm), _arch_dup_mmap(mm))
+
 #endif
Index: head-2006-06-07/include/asm-i386/mach-xen/asm/mmu_context.h
===================================================================
--- head-2006-06-07.orig/include/asm-i386/mach-xen/asm/mmu_context.h	2006-06-08 12:41:06.000000000 +0200
+++ head-2006-06-07/include/asm-i386/mach-xen/asm/mmu_context.h	2006-06-08 12:41:33.000000000 +0200
@@ -51,8 +51,7 @@ static inline void switch_mm(struct mm_s
 	struct mmuext_op _op[2], *op = _op;
 
 	if (likely(prev != next)) {
-		if (!test_bit(PG_pinned, &virt_to_page(next->pgd)->flags))
-			mm_pin(next);
+		BUG_ON(!test_bit(PG_pinned, &virt_to_page(next->pgd)->flags));
 
 		/* stop flush ipis for the previous mm */
 		cpu_clear(cpu, prev->cpu_vm_mask);
@@ -99,7 +98,11 @@ static inline void switch_mm(struct mm_s
 #define deactivate_mm(tsk, mm) \
 	asm("movl %0,%%fs ; movl %0,%%gs": :"r" (0))
 
-#define activate_mm(prev, next) \
-	switch_mm((prev),(next),NULL)
+static inline void activate_mm(struct mm_struct *prev, struct mm_struct *next)
+{
+	if (!test_bit(PG_pinned, &virt_to_page(next->pgd)->flags))
+		mm_pin(next);
+	switch_mm(prev, next, NULL);
+}
 
 #endif
Index: head-2006-06-07/include/asm-x86_64/mach-xen/asm/mmu.h
===================================================================
--- head-2006-06-07.orig/include/asm-x86_64/mach-xen/asm/mmu.h	2006-06-08 12:41:06.000000000 +0200
+++ head-2006-06-07/include/asm-x86_64/mach-xen/asm/mmu.h	2006-06-08 12:41:33.000000000 +0200
@@ -28,6 +28,10 @@ extern spinlock_t mm_unpinned_lock;
 /* mm/memory.c:exit_mmap hook */
 extern void _arch_exit_mmap(struct mm_struct *mm);
 #define arch_exit_mmap(_mm) _arch_exit_mmap(_mm)
+
+/* kernel/fork.c:dup_mmap hook */
+extern void _arch_dup_mmap(struct mm_struct *mm);
+#define arch_dup_mmap(mm, oldmm) ((void)(oldmm), _arch_dup_mmap(mm))
 #endif
 
 #endif
Index: head-2006-06-07/include/asm-x86_64/mach-xen/asm/mmu_context.h
===================================================================
--- head-2006-06-07.orig/include/asm-x86_64/mach-xen/asm/mmu_context.h	2006-06-08 12:41:06.000000000 +0200
+++ head-2006-06-07/include/asm-x86_64/mach-xen/asm/mmu_context.h	2006-06-08 12:41:33.000000000 +0200
@@ -73,8 +73,7 @@ static inline void switch_mm(struct mm_s
 	struct mmuext_op _op[3], *op = _op;
 
 	if (likely(prev != next)) {
-		if (!next->context.pinned)
-			mm_pin(next);
+		BUG_ON(!next->context.pinned);
 
 		/* stop flush ipis for the previous mm */
 		clear_bit(cpu, &prev->cpu_vm_mask);
@@ -127,8 +126,11 @@ static inline void switch_mm(struct mm_s
 	asm volatile("movl %0,%%fs"::"r"(0));  \
 } while(0)
 
-#define activate_mm(prev, next) do {		\
-	switch_mm((prev),(next),NULL);		\
-} while (0)
+static inline void activate_mm(struct mm_struct *prev, struct mm_struct *next)
+{
+	if (!next->context.pinned)
+		mm_pin(next);
+	switch_mm(prev, next, NULL);
+}
 
 #endif
Index: head-2006-06-07/kernel/fork.c
===================================================================
--- head-2006-06-07.orig/kernel/fork.c	2006-06-08 12:41:06.000000000 +0200
+++ head-2006-06-07/kernel/fork.c	2006-06-08 12:41:33.000000000 +0200
@@ -280,6 +280,9 @@ static inline int dup_mmap(struct mm_str
 		if (retval)
 			goto out;
 	}
+#ifdef arch_dup_mmap
+	arch_dup_mmap(mm, oldmm);
+#endif
 	retval = 0;
 out:
 	up_write(&mm->mmap_sem);