--- a/include/linux/compat.h~mm-simplify-compat-numa-syscalls
+++ a/include/linux/compat.h
@@ -395,14 +395,6 @@ struct compat_kexec_segment;
 struct compat_mq_attr;
 struct compat_msgbuf;
 
-#define BITS_PER_COMPAT_LONG    (8*sizeof(compat_long_t))
-
-#define BITS_TO_COMPAT_LONGS(bits) DIV_ROUND_UP(bits, BITS_PER_COMPAT_LONG)
-
-long compat_get_bitmap(unsigned long *mask, const compat_ulong_t __user *umask,
-		       unsigned long bitmap_size);
-long compat_put_bitmap(compat_ulong_t __user *umask, unsigned long *mask,
-		       unsigned long bitmap_size);
 void copy_siginfo_to_external32(struct compat_siginfo *to,
 		const struct kernel_siginfo *from);
 int copy_siginfo_from_user32(kernel_siginfo_t *to,
@@ -976,6 +968,15 @@ static inline bool in_compat_syscall(voi
 
 #endif /* CONFIG_COMPAT */
 
+#define BITS_PER_COMPAT_LONG    (8*sizeof(compat_long_t))
+
+#define BITS_TO_COMPAT_LONGS(bits) DIV_ROUND_UP(bits, BITS_PER_COMPAT_LONG)
+
+long compat_get_bitmap(unsigned long *mask, const compat_ulong_t __user *umask,
+		       unsigned long bitmap_size);
+long compat_put_bitmap(compat_ulong_t __user *umask, unsigned long *mask,
+		       unsigned long bitmap_size);
+
 /*
  * Some legacy ABIs like the i386 one use less than natural alignment for 64-bit
  * types, and will need special compat treatment for that.  Most architectures
--- a/mm/mempolicy.c~mm-simplify-compat-numa-syscalls
+++ a/mm/mempolicy.c
@@ -1362,16 +1362,33 @@ mpol_out:
 /*
  * User space interface with variable sized bitmaps for nodelists.
  */
+static int get_bitmap(unsigned long *mask, const unsigned long __user *nmask,
+		      unsigned long maxnode)
+{
+	unsigned long nlongs = BITS_TO_LONGS(maxnode);
+	int ret;
+
+	if (in_compat_syscall())
+		ret = compat_get_bitmap(mask,
+					(const compat_ulong_t __user *)nmask,
+					maxnode);
+	else
+		ret = copy_from_user(mask, nmask,
+				     nlongs * sizeof(unsigned long));
+
+	if (ret)
+		return -EFAULT;
+
+	if (maxnode % BITS_PER_LONG)
+		mask[nlongs - 1] &= (1UL << (maxnode % BITS_PER_LONG)) - 1;
+
+	return 0;
+}
 
 /* Copy a node mask from user space. */
 static int get_nodes(nodemask_t *nodes, const unsigned long __user *nmask,
 		     unsigned long maxnode)
 {
-	unsigned long k;
-	unsigned long t;
-	unsigned long nlongs;
-	unsigned long endmask;
-
 	--maxnode;
 	nodes_clear(*nodes);
 	if (maxnode == 0 || !nmask)
@@ -1379,49 +1396,29 @@ static int get_nodes(nodemask_t *nodes,
 	if (maxnode > PAGE_SIZE*BITS_PER_BYTE)
 		return -EINVAL;
 
-	nlongs = BITS_TO_LONGS(maxnode);
-	if ((maxnode % BITS_PER_LONG) == 0)
-		endmask = ~0UL;
-	else
-		endmask = (1UL << (maxnode % BITS_PER_LONG)) - 1;
-
 	/*
 	 * When the user specified more nodes than supported just check
-	 * if the non supported part is all zero.
-	 *
-	 * If maxnode have more longs than MAX_NUMNODES, check
-	 * the bits in that area first. And then go through to
-	 * check the rest bits which equal or bigger than MAX_NUMNODES.
-	 * Otherwise, just check bits [MAX_NUMNODES, maxnode).
+	 * if the non supported part is all zero, one word at a time,
+	 * starting at the end.
 	 */
-	if (nlongs > BITS_TO_LONGS(MAX_NUMNODES)) {
-		for (k = BITS_TO_LONGS(MAX_NUMNODES); k < nlongs; k++) {
-			if (get_user(t, nmask + k))
-				return -EFAULT;
-			if (k == nlongs - 1) {
-				if (t & endmask)
-					return -EINVAL;
-			} else if (t)
-				return -EINVAL;
-		}
-		nlongs = BITS_TO_LONGS(MAX_NUMNODES);
-		endmask = ~0UL;
-	}
-
-	if (maxnode > MAX_NUMNODES && MAX_NUMNODES % BITS_PER_LONG != 0) {
-		unsigned long valid_mask = endmask;
+	while (maxnode > MAX_NUMNODES) {
+		unsigned long bits = min_t(unsigned long, maxnode, BITS_PER_LONG);
+		unsigned long t;
 
-		valid_mask &= ~((1UL << (MAX_NUMNODES % BITS_PER_LONG)) - 1);
-		if (get_user(t, nmask + nlongs - 1))
+		if (get_bitmap(&t, &nmask[maxnode / BITS_PER_LONG], bits))
 			return -EFAULT;
-		if (t & valid_mask)
+
+		if (maxnode - bits >= MAX_NUMNODES) {
+			maxnode -= bits;
+		} else {
+			maxnode = MAX_NUMNODES;
+			t &= ~((1UL << (MAX_NUMNODES % BITS_PER_LONG)) - 1);
+		}
+		if (t)
 			return -EINVAL;
 	}
 
-	if (copy_from_user(nodes_addr(*nodes), nmask, nlongs*sizeof(unsigned long)))
-		return -EFAULT;
-	nodes_addr(*nodes)[nlongs-1] &= endmask;
-	return 0;
+	return get_bitmap(nodes_addr(*nodes), nmask, maxnode);
 }
 
 /* Copy a kernel node mask to user space */
@@ -1430,6 +1427,10 @@ static int copy_nodes_to_user(unsigned l
 {
 	unsigned long copy = ALIGN(maxnode-1, 64) / 8;
 	unsigned int nbytes = BITS_TO_LONGS(nr_node_ids) * sizeof(long);
+	bool compat = in_compat_syscall();
+
+	if (compat)
+		nbytes = BITS_TO_COMPAT_LONGS(nr_node_ids) * sizeof(compat_long_t);
 
 	if (copy > nbytes) {
 		if (copy > PAGE_SIZE)
@@ -1437,7 +1438,13 @@ static int copy_nodes_to_user(unsigned l
 		if (clear_user((char __user *)mask + nbytes, copy - nbytes))
 			return -EFAULT;
 		copy = nbytes;
+		maxnode = nr_node_ids;
 	}
+
+	if (compat)
+		return compat_put_bitmap((compat_ulong_t __user *)mask,
+					 nodes_addr(*nodes), maxnode);
+
 	return copy_to_user(mask, nodes_addr(*nodes), copy) ? -EFAULT : 0;
 }
 
@@ -1649,72 +1656,22 @@ COMPAT_SYSCALL_DEFINE5(get_mempolicy, in
 		       compat_ulong_t, maxnode,
 		       compat_ulong_t, addr, compat_ulong_t, flags)
 {
-	long err;
-	unsigned long __user *nm = NULL;
-	unsigned long nr_bits, alloc_size;
-	DECLARE_BITMAP(bm, MAX_NUMNODES);
-
-	nr_bits = min_t(unsigned long, maxnode-1, nr_node_ids);
-	alloc_size = ALIGN(nr_bits, BITS_PER_LONG) / 8;
-
-	if (nmask)
-		nm = compat_alloc_user_space(alloc_size);
-
-	err = kernel_get_mempolicy(policy, nm, nr_bits+1, addr, flags);
-
-	if (!err && nmask) {
-		unsigned long copy_size;
-		copy_size = min_t(unsigned long, sizeof(bm), alloc_size);
-		err = copy_from_user(bm, nm, copy_size);
-		/* ensure entire bitmap is zeroed */
-		err |= clear_user(nmask, ALIGN(maxnode-1, 8) / 8);
-		err |= compat_put_bitmap(nmask, bm, nr_bits);
-	}
-
-	return err;
+	return kernel_get_mempolicy(policy, (unsigned long __user *)nmask,
+				    maxnode, addr, flags);
 }
 
 COMPAT_SYSCALL_DEFINE3(set_mempolicy, int, mode, compat_ulong_t __user *, nmask,
 		       compat_ulong_t, maxnode)
 {
-	unsigned long __user *nm = NULL;
-	unsigned long nr_bits, alloc_size;
-	DECLARE_BITMAP(bm, MAX_NUMNODES);
-
-	nr_bits = min_t(unsigned long, maxnode-1, MAX_NUMNODES);
-	alloc_size = ALIGN(nr_bits, BITS_PER_LONG) / 8;
-
-	if (nmask) {
-		if (compat_get_bitmap(bm, nmask, nr_bits))
-			return -EFAULT;
-		nm = compat_alloc_user_space(alloc_size);
-		if (copy_to_user(nm, bm, alloc_size))
-			return -EFAULT;
-	}
-
-	return kernel_set_mempolicy(mode, nm, nr_bits+1);
+	return kernel_set_mempolicy(mode, (unsigned long __user *)nmask, maxnode);
 }
 
 COMPAT_SYSCALL_DEFINE6(mbind, compat_ulong_t, start, compat_ulong_t, len,
 		       compat_ulong_t, mode, compat_ulong_t __user *, nmask,
 		       compat_ulong_t, maxnode, compat_ulong_t, flags)
 {
-	unsigned long __user *nm = NULL;
-	unsigned long nr_bits, alloc_size;
-	nodemask_t bm;
-
-	nr_bits = min_t(unsigned long, maxnode-1, MAX_NUMNODES);
-	alloc_size = ALIGN(nr_bits, BITS_PER_LONG) / 8;
-
-	if (nmask) {
-		if (compat_get_bitmap(nodes_addr(bm), nmask, nr_bits))
-			return -EFAULT;
-		nm = compat_alloc_user_space(alloc_size);
-		if (copy_to_user(nm, nodes_addr(bm), alloc_size))
-			return -EFAULT;
-	}
-
-	return kernel_mbind(start, len, mode, nm, nr_bits+1, flags);
+	return kernel_mbind(start, len, mode, (unsigned long __user *)nmask,
+			    maxnode, flags);
 }
 
 COMPAT_SYSCALL_DEFINE4(migrate_pages, compat_pid_t, pid,
@@ -1722,32 +1679,9 @@ COMPAT_SYSCALL_DEFINE4(migrate_pages, co
 		       const compat_ulong_t __user *, old_nodes,
 		       const compat_ulong_t __user *, new_nodes)
 {
-	unsigned long __user *old = NULL;
-	unsigned long __user *new = NULL;
-	nodemask_t tmp_mask;
-	unsigned long nr_bits;
-	unsigned long size;
-
-	nr_bits = min_t(unsigned long, maxnode - 1, MAX_NUMNODES);
-	size = ALIGN(nr_bits, BITS_PER_LONG) / 8;
-	if (old_nodes) {
-		if (compat_get_bitmap(nodes_addr(tmp_mask), old_nodes, nr_bits))
-			return -EFAULT;
-		old = compat_alloc_user_space(new_nodes ? size * 2 : size);
-		if (new_nodes)
-			new = old + size / sizeof(unsigned long);
-		if (copy_to_user(old, nodes_addr(tmp_mask), size))
-			return -EFAULT;
-	}
-	if (new_nodes) {
-		if (compat_get_bitmap(nodes_addr(tmp_mask), new_nodes, nr_bits))
-			return -EFAULT;
-		if (new == NULL)
-			new = compat_alloc_user_space(size);
-		if (copy_to_user(new, nodes_addr(tmp_mask), size))
-			return -EFAULT;
-	}
-	return kernel_migrate_pages(pid, nr_bits + 1, old, new);
+	return kernel_migrate_pages(pid, maxnode,
+				    (const unsigned long __user *)old_nodes,
+				    (const unsigned long __user *)new_nodes);
 }
 
 #endif /* CONFIG_COMPAT */
