Replace mfn_to_page(lXe_get_pfn()) by lXe_get_page().

However, what I got surprised by while looking for all of these is that
ptwr_emulated_update() uses gmfn_to_mfn() on the pte loaded from the
emulation context, while ptwr_do_page_fault() doesn't on the pte stored
into that context. Shouldn't these two be symmetric?

Index: 2007-02-20/xen/arch/x86/mm.c
===================================================================
--- 2007-02-20.orig/xen/arch/x86/mm.c	2007-02-20 10:55:57.000000000 +0100
+++ 2007-02-20/xen/arch/x86/mm.c	2007-02-20 10:56:12.000000000 +0100
@@ -794,7 +794,7 @@ static void put_page_from_l2e(l2_pgentry
 {
     if ( (l2e_get_flags(l2e) & _PAGE_PRESENT) && 
          (l2e_get_pfn(l2e) != pfn) )
-        put_page_and_type(mfn_to_page(l2e_get_pfn(l2e)));
+        put_page_and_type(l2e_get_page(l2e));
 }
 
 
@@ -803,7 +803,7 @@ static void put_page_from_l3e(l3_pgentry
 {
     if ( (l3e_get_flags(l3e) & _PAGE_PRESENT) && 
          (l3e_get_pfn(l3e) != pfn) )
-        put_page_and_type(mfn_to_page(l3e_get_pfn(l3e)));
+        put_page_and_type(l3e_get_page(l3e));
 }
 #endif
 
@@ -812,7 +812,7 @@ static void put_page_from_l4e(l4_pgentry
 {
     if ( (l4e_get_flags(l4e) & _PAGE_PRESENT) && 
          (l4e_get_pfn(l4e) != pfn) )
-        put_page_and_type(mfn_to_page(l4e_get_pfn(l4e)));
+        put_page_and_type(l4e_get_page(l4e));
 }
 #endif
 
@@ -3369,7 +3369,6 @@ int ptwr_do_page_fault(struct vcpu *v, u
                        struct cpu_user_regs *regs)
 {
     struct domain *d = v->domain;
-    unsigned long     pfn;
     struct page_info *page;
     l1_pgentry_t      pte;
     struct ptwr_emulate_ctxt ptwr_ctxt;
@@ -3383,8 +3382,7 @@ int ptwr_do_page_fault(struct vcpu *v, u
     guest_get_eff_l1e(v, addr, &pte);
     if ( !(l1e_get_flags(pte) & _PAGE_PRESENT) )
         goto bail;
-    pfn  = l1e_get_pfn(pte);
-    page = mfn_to_page(pfn);
+    page = l1e_get_page(pte);
 
     /* We are looking only for read-only mappings of p.t. pages. */
     if ( ((l1e_get_flags(pte) & (_PAGE_PRESENT|_PAGE_RW)) != _PAGE_PRESENT) ||