mem: Add a MemBackdoor type to track memory backdoors.

These are similar to the structures TLM's DMI mechanism uses. Instead
of having an invalidation broadcast which propogates backwards up the
port hierarchy, this mechanism tracks a set of callbacks which are
triggered when a back door is invalidated to let other holders clean
up their bookkeeping.

Change-Id: If24489258dcaee14d7b6e5b996dfb1c2636f26ab
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17589
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>

diff --git a/src/mem/backdoor.hh b/src/mem/backdoor.hh
new file mode 100644 (file)
index 0000000..24db2c9
--- /dev/null
+++ b/src/mem/backdoor.hh
@@ -0,0 +1,154 @@
+/*
+ * Copyright 2019 Google, Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Gabe Black
+ */
+
+#ifndef __MEM_BACKDOOR_HH__
+#define __MEM_BACKDOOR_HH__
+
+#include <cstdint>
+#include <functional>
+#include <memory>
+
+#include "base/addr_range.hh"
+#include "base/callback.hh"
+
+class MemBackdoor
+{
+  public:
+    // Callbacks from this back door are set up using a callable which accepts
+    // a const reference to this back door as their only parameter.
+    typedef std::function<void(const MemBackdoor &backdoor)> CbFunction;
+
+  private:
+    // This wrapper class holds the callables described above so that they
+    // can be stored in a generic CallbackQueue.
+    class Callback : public ::Callback
+    {
+      public:
+        Callback(MemBackdoor &bd, CbFunction cb) :
+            _backdoor(bd), cbFunction(cb)
+        {}
+
+        void process() override { cbFunction(_backdoor); }
+        // It looks like this is only called when the CallbackQueue is
+        // destroyed and this Callback is currently in the queue.
+        void autoDestruct() override { delete this; }
+
+        MemBackdoor &backdoor() { return _backdoor; }
+
+      private:
+        MemBackdoor &_backdoor;
+        CbFunction cbFunction;
+    };
+
+  public:
+    enum Flags{
+        // How data is allowed to be accessed through this backdoor.
+        NoAccess = 0x0,
+        Readable = 0x1,
+        Writeable = 0x2
+    };
+
+    // The range in the guest address space covered by this back door.
+    const AddrRange &range() const { return _range; }
+    void range(const AddrRange &r) { _range = r; }
+
+    // A pointer to the data accessible through this back door.
+    uint8_t *ptr() const { return _ptr; }
+    void ptr(uint8_t *p) { _ptr = p; }
+
+    /*
+     * Helper functions to make it easier to set/check particular flags.
+     */
+
+    bool readable() const { return _flags & Readable; }
+    void
+    readable(bool r)
+    {
+        if (r)
+            _flags = (Flags)(_flags | Readable);
+        else
+            _flags = (Flags)(_flags & ~Readable);
+    }
+
+    bool writeable() const { return _flags & Writeable; }
+    void
+    writeable(bool w)
+    {
+        if (w)
+            _flags = (Flags)(_flags | Writeable);
+        else
+            _flags = (Flags)(_flags & ~Writeable);
+    }
+
+    Flags flags() const { return _flags; }
+    void flags(Flags f) { _flags = f; }
+
+    MemBackdoor(AddrRange r, uint8_t *p, Flags flags) :
+        invalidationCallbacks(new CallbackQueue),
+        _range(r), _ptr(p), _flags(flags)
+    {}
+
+    MemBackdoor() : MemBackdoor(AddrRange(), nullptr, NoAccess)
+    {}
+
+    // Set up a callable to be called when this back door is invalidated. This
+    // lets holders update their bookkeeping to remove any references to it,
+    // and/or to propogate that invalidation to other interested parties.
+    void
+    addInvalidationCallback(CbFunction func)
+    {
+        auto *cb = new MemBackdoor::Callback(*this, func);
+        assert(cb);
+        invalidationCallbacks->add(cb);
+    }
+
+    // Notify and clear invalidation callbacks when the data in the backdoor
+    // structure is no longer valid/current. The backdoor might then be
+    // updated or even deleted without having to worry about stale data being
+    // used.
+    void
+    invalidate()
+    {
+        invalidationCallbacks->process();
+        // Delete and recreate the callback queue to ensure the callback
+        // objects are deleted.
+        invalidationCallbacks.reset(new CallbackQueue());
+    }
+
+  private:
+    std::unique_ptr<CallbackQueue> invalidationCallbacks;
+
+    AddrRange _range;
+    uint8_t *_ptr;
+    Flags _flags;
+};
+
+typedef MemBackdoor *MemBackdoorPtr;
+
+#endif  //__MEM_BACKDOOR_HH__