diff --git a/src/main/scala/rocket/TLBPermissions.scala b/src/main/scala/rocket/TLBPermissions.scala
new file mode 100644
index 00000000..58e984de
--- /dev/null
+++ b/src/main/scala/rocket/TLBPermissions.scala
@@ -0,0 +1,97 @@
+// See LICENSE.SiFive for license details.
+
+package rocket
+
+import Chisel._
+import diplomacy._
+import uncore.tilelink2._
+
+case class TLBPermissions(
+  homogeneous: Bool, // if false, the below are undefined
+  r: Bool, // readable
+  w: Bool, // writeable
+  x: Bool, // executable
+  c: Bool, // cacheable
+  a: Bool, // arithmetic ops
+  l: Bool) // logical ops
+
+object TLBPageLookup
+{
+  private case class TLBFixedPermissions(
+    r: Boolean, // readable
+    w: Boolean, // writeable
+    x: Boolean, // executable
+    c: Boolean, // cacheable
+    a: Boolean, // arithmetic ops
+    l: Boolean) { // logical ops
+    val useful = r || w || x || c || a || l
+  }
+
+  // Unmapped memory is considered to be inhomogeneous
+  def apply(managers: Seq[TLManagerParameters], xLen: Int, cacheBlockBytes: Int, pageSize: BigInt): UInt => TLBPermissions = {
+    require (isPow2(xLen) && xLen >= 8)
+    require (isPow2(cacheBlockBytes) && cacheBlockBytes >= xLen/8)
+    require (isPow2(pageSize) && pageSize >= cacheBlockBytes)
+
+    val xferSizes = TransferSizes(cacheBlockBytes, cacheBlockBytes)
+    val allSizes = TransferSizes(1, cacheBlockBytes)
+    val amoSizes = TransferSizes(4, xLen/8)
+
+    val permissions = managers.map { m =>
+      require (!m.supportsGet        || m.supportsGet       .contains(allSizes),  s"MemoryMap region ${m.name} only supports ${m.supportsGet} Get, but must support ${allSizes}")
+      require (!m.supportsPutFull    || m.supportsPutFull   .contains(allSizes),  s"MemoryMap region ${m.name} only supports ${m.supportsPutFull} PutFull, but must support ${allSizes}")
+      require (!m.supportsAcquireB   || m.supportsAcquireB  .contains(xferSizes), s"MemoryMap region ${m.name} only supports ${m.supportsAcquireB} AcquireB, but must support ${xferSizes}")
+      require (!m.supportsAcquireT   || m.supportsAcquireT  .contains(xferSizes), s"MemoryMap region ${m.name} only supports ${m.supportsAcquireT} AcquireT, but must support ${xferSizes}")
+      require (!m.supportsLogical    || m.supportsLogical   .contains(amoSizes),  s"MemoryMap region ${m.name} only supports ${m.supportsLogical} Logical, but must support ${amoSizes}")
+      require (!m.supportsArithmetic || m.supportsArithmetic.contains(amoSizes),  s"MemoryMap region ${m.name} only supports ${m.supportsArithmetic} Arithmetic, but must support ${amoSizes}")
+      require (m.supportsAcquireT || !m.supportsAcquireB, s"MemoryMap region ${m.name} supports AcquireB (cached read) but not AcquireT (cached write)... and rocket assumes this")
+
+      (m.address, TLBFixedPermissions(
+        r = m.supportsGet     || m.supportsAcquireB, // if cached, never uses Get
+        w = m.supportsPutFull || m.supportsAcquireT, // if cached, never uses Put
+        x = m.executable,
+        c = m.supportsAcquireB,
+        a = m.supportsArithmetic,
+        l = m.supportsLogical))
+    }
+
+    val grouped: Map[TLBFixedPermissions, Seq[AddressSet]] = permissions
+      .filter(_._2.useful) // get rid of no-permission devices
+      .groupBy(_._2) // group by permission type
+      .mapValues(seq => 
+        AddressSet.unify(seq.flatMap(_._1)) // coalesce same-permission regions
+        .filter(_.alignment >= pageSize)) // discard any region that's not big enough
+
+    def lowCostProperty(prop: TLBFixedPermissions => Boolean): UInt => Bool = {
+      val (yesm, nom) = grouped.partition { case (k, eq) => prop(k) }
+      val (yes, no) = (yesm.values.flatten.toList, nom.values.flatten.toList)
+      // Find the minimal bits needed to distinguish between yes and no
+      val decisionMask = AddressDecoder(Seq(yes, no))
+      def simplify(x: Seq[AddressSet]) = AddressSet.unify(x.map(_.widen(~decisionMask)).distinct)
+      val (yesf, nof) = (simplify(yes), simplify(no))
+      if (yesf.size < no.size) {
+        (x: UInt) => yesf.map(_.contains(x)).reduce(_ || _)
+      } else {
+        (x: UInt) => !nof.map(_.contains(x)).reduce(_ || _)
+      }
+    }
+
+    // Derive simplified property circuits (don't care when !homo)
+    val rfn = lowCostProperty(_.r)
+    val wfn = lowCostProperty(_.w)
+    val xfn = lowCostProperty(_.x)
+    val cfn = lowCostProperty(_.c)
+    val afn = lowCostProperty(_.a)
+    val lfn = lowCostProperty(_.l)
+
+    val homo = AddressSet.unify(grouped.values.flatten.toList)
+    (x: UInt) => TLBPermissions(
+      homogeneous = homo.map(_.contains(x)).reduce(_ || _),
+      r = rfn(x),
+      w = wfn(x),
+      x = xfn(x),
+      c = cfn(x),
+      a = afn(x),
+      l = lfn(x))
+  }
+}