Index: src/module/cmemk.c
===================================================================
--- src/module/cmemk.c	(revision 14484)
+++ src/module/cmemk.c	(working copy)
@@ -95,6 +95,17 @@
 
 #endif /* LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,18) */
 
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,31)
+
+/*
+ * Linux 2.6.31 introduced the follow_pfn function which can be
+ * used to find the PFN for a user virtual address for certain
+ * kinds of mappings.
+ */
+#define USE_FOLLOW_PFN
+
+#endif /* LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,31) */
+
 #include "../interface/cmem.h"
 
 /*
@@ -562,6 +573,9 @@ static unsigned long get_phys(unsigned long virtp)
     struct mm_struct *mm = current->mm;
     struct vm_area_struct *vma;
     int bi;
+#ifdef USE_FOLLOW_PFN
+    unsigned long pfn;
+#endif
 
     /* For CMEM block kernel addresses */
     for (bi = 0; bi < NBLOCKS; bi++) {
@@ -579,18 +593,29 @@ static unsigned long get_phys(unsigned long virtp)
         physp = virt_to_phys((void *)virtp);
         __D("get_phys: virt_to_phys translated direct-mapped %#lx to %#lx\n",
             virtp, physp);
+        return physp;
     }
 
     /* this will catch, kernel-allocated, mmaped-to-usermode addresses */
-    else if ((vma = find_vma(mm, virtp)) &&
-             (vma->vm_flags & VM_IO) &&
-             (vma->vm_pgoff)) {
+    vma = find_vma(mm, virtp);
+#ifdef USE_FOLLOW_PFN
+    if (vma && follow_pfn(vma, (virtp & PAGE_MASK), &pfn) == 0) {
+        physp = (pfn << PAGE_SHIFT) | (virtp & ~PAGE_MASK);
+        __D("get_phys: find_vma + follow_pfn translated user %#lx to %#lx\n",
+            virtp, physp);
+        return physp;
+    }
+#else
+    if (vma && (vma->vm_flags & VM_IO) && (vma->vm_pgoff)) {
         physp =  (vma->vm_pgoff << PAGE_SHIFT) + (virtp - vma->vm_start);
-        __D("get_phys: find_vma translated user %#lx to %#lx\n", virtp, physp);
+        __D("get_phys: find_vma + vm_pgoff translated user %#lx to %#lx\n",
+            virtp, physp);
+        return physp;
     }
+#endif
 
     /* otherwise, use get_user_pages() for general userland pages */
-    else {
+    {
         int res, nr_pages = 1;
         struct page *pages;