src/mem/backdoor.hh

   1 /*
   2  * Copyright 2019 Google, Inc.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions are
   6  * met: redistributions of source code must retain the above copyright
   7  * notice, this list of conditions and the following disclaimer;
   8  * redistributions in binary form must reproduce the above copyright
   9  * notice, this list of conditions and the following disclaimer in the
  10  * documentation and/or other materials provided with the distribution;
  11  * neither the name of the copyright holders nor the names of its
  12  * contributors may be used to endorse or promote products derived from
  13  * this software without specific prior written permission.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  16  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  17  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  18  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  19  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  20  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  21  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  22  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  23  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  24  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  25  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  26  */
  27
  28 #ifndef __MEM_BACKDOOR_HH__
  29 #define __MEM_BACKDOOR_HH__
  30
  31 #include <cstdint>
  32 #include <functional>
  33 #include <memory>
  34
  35 #include "base/addr_range.hh"
  36 #include "base/callback.hh"
  37
  38 class MemBackdoor
  39 {
  40   public:
  41     // Callbacks from this back door are set up using a callable which accepts
  42     // a const reference to this back door as their only parameter.
  43     typedef std::function<void(const MemBackdoor &backdoor)> CbFunction;
  44
  45   private:
  46     // This wrapper class holds the callables described above so that they
  47     // can be stored in a generic CallbackQueue.
  48     class Callback : public ::Callback
  49     {
  50       public:
  51         Callback(MemBackdoor &bd, CbFunction cb) :
  52             _backdoor(bd), cbFunction(cb)
  53         {}
  54
  55         void process() override { cbFunction(_backdoor); }
  56         // It looks like this is only called when the CallbackQueue is
  57         // destroyed and this Callback is currently in the queue.
  58         void autoDestruct() override { delete this; }
  59
  60         MemBackdoor &backdoor() { return _backdoor; }
  61
  62       private:
  63         MemBackdoor &_backdoor;
  64         CbFunction cbFunction;
  65     };
  66
  67   public:
  68     enum Flags{
  69         // How data is allowed to be accessed through this backdoor.
  70         NoAccess = 0x0,
  71         Readable = 0x1,
  72         Writeable = 0x2
  73     };
  74
  75     // The range in the guest address space covered by this back door.
  76     const AddrRange &range() const { return _range; }
  77     void range(const AddrRange &r) { _range = r; }
  78
  79     // A pointer to the data accessible through this back door.
  80     uint8_t *ptr() const { return _ptr; }
  81     void ptr(uint8_t *p) { _ptr = p; }
  82
  83     /*
  84      * Helper functions to make it easier to set/check particular flags.
  85      */
  86
  87     bool readable() const { return _flags & Readable; }
  88     void
  89     readable(bool r)
  90     {
  91         if (r)
  92             _flags = (Flags)(_flags | Readable);
  93         else
  94             _flags = (Flags)(_flags & ~Readable);
  95     }
  96
  97     bool writeable() const { return _flags & Writeable; }
  98     void
  99     writeable(bool w)
 100     {
 101         if (w)
 102             _flags = (Flags)(_flags | Writeable);
 103         else
 104             _flags = (Flags)(_flags & ~Writeable);
 105     }
 106
 107     Flags flags() const { return _flags; }
 108     void flags(Flags f) { _flags = f; }
 109
 110     MemBackdoor(AddrRange r, uint8_t *p, Flags flags) :
 111         invalidationCallbacks(new CallbackQueue),
 112         _range(r), _ptr(p), _flags(flags)
 113     {}
 114
 115     MemBackdoor() : MemBackdoor(AddrRange(), nullptr, NoAccess)
 116     {}
 117
 118     // Set up a callable to be called when this back door is invalidated. This
 119     // lets holders update their bookkeeping to remove any references to it,
 120     // and/or to propogate that invalidation to other interested parties.
 121     void
 122     addInvalidationCallback(CbFunction func)
 123     {
 124         auto *cb = new MemBackdoor::Callback(*this, func);
 125         assert(cb);
 126         invalidationCallbacks->add(cb);
 127     }
 128
 129     // Notify and clear invalidation callbacks when the data in the backdoor
 130     // structure is no longer valid/current. The backdoor might then be
 131     // updated or even deleted without having to worry about stale data being
 132     // used.
 133     void
 134     invalidate()
 135     {
 136         invalidationCallbacks->process();
 137         // Delete and recreate the callback queue to ensure the callback
 138         // objects are deleted.
 139         invalidationCallbacks.reset(new CallbackQueue());
 140     }
 141
 142   private:
 143     std::unique_ptr<CallbackQueue> invalidationCallbacks;
 144
 145     AddrRange _range;
 146     uint8_t *_ptr;
 147     Flags _flags;
 148 };
 149
 150 typedef MemBackdoor *MemBackdoorPtr;
 151
 152 #endif  //__MEM_BACKDOOR_HH__