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  * Authors: Gabe Black
  28  */
  29
  30 #ifndef __MEM_BACKDOOR_HH__
  31 #define __MEM_BACKDOOR_HH__
  32
  33 #include <cstdint>
  34 #include <functional>
  35 #include <memory>
  36
  37 #include "base/addr_range.hh"
  38 #include "base/callback.hh"
  39
  40 class MemBackdoor
  41 {
  42   public:
  43     // Callbacks from this back door are set up using a callable which accepts
  44     // a const reference to this back door as their only parameter.
  45     typedef std::function<void(const MemBackdoor &backdoor)> CbFunction;
  46
  47   private:
  48     // This wrapper class holds the callables described above so that they
  49     // can be stored in a generic CallbackQueue.
  50     class Callback : public ::Callback
  51     {
  52       public:
  53         Callback(MemBackdoor &bd, CbFunction cb) :
  54             _backdoor(bd), cbFunction(cb)
  55         {}
  56
  57         void process() override { cbFunction(_backdoor); }
  58         // It looks like this is only called when the CallbackQueue is
  59         // destroyed and this Callback is currently in the queue.
  60         void autoDestruct() override { delete this; }
  61
  62         MemBackdoor &backdoor() { return _backdoor; }
  63
  64       private:
  65         MemBackdoor &_backdoor;
  66         CbFunction cbFunction;
  67     };
  68
  69   public:
  70     enum Flags{
  71         // How data is allowed to be accessed through this backdoor.
  72         NoAccess = 0x0,
  73         Readable = 0x1,
  74         Writeable = 0x2
  75     };
  76
  77     // The range in the guest address space covered by this back door.
  78     const AddrRange &range() const { return _range; }
  79     void range(const AddrRange &r) { _range = r; }
  80
  81     // A pointer to the data accessible through this back door.
  82     uint8_t *ptr() const { return _ptr; }
  83     void ptr(uint8_t *p) { _ptr = p; }
  84
  85     /*
  86      * Helper functions to make it easier to set/check particular flags.
  87      */
  88
  89     bool readable() const { return _flags & Readable; }
  90     void
  91     readable(bool r)
  92     {
  93         if (r)
  94             _flags = (Flags)(_flags | Readable);
  95         else
  96             _flags = (Flags)(_flags & ~Readable);
  97     }
  98
  99     bool writeable() const { return _flags & Writeable; }
 100     void
 101     writeable(bool w)
 102     {
 103         if (w)
 104             _flags = (Flags)(_flags | Writeable);
 105         else
 106             _flags = (Flags)(_flags & ~Writeable);
 107     }
 108
 109     Flags flags() const { return _flags; }
 110     void flags(Flags f) { _flags = f; }
 111
 112     MemBackdoor(AddrRange r, uint8_t *p, Flags flags) :
 113         invalidationCallbacks(new CallbackQueue),
 114         _range(r), _ptr(p), _flags(flags)
 115     {}
 116
 117     MemBackdoor() : MemBackdoor(AddrRange(), nullptr, NoAccess)
 118     {}
 119
 120     // Set up a callable to be called when this back door is invalidated. This
 121     // lets holders update their bookkeeping to remove any references to it,
 122     // and/or to propogate that invalidation to other interested parties.
 123     void
 124     addInvalidationCallback(CbFunction func)
 125     {
 126         auto *cb = new MemBackdoor::Callback(*this, func);
 127         assert(cb);
 128         invalidationCallbacks->add(cb);
 129     }
 130
 131     // Notify and clear invalidation callbacks when the data in the backdoor
 132     // structure is no longer valid/current. The backdoor might then be
 133     // updated or even deleted without having to worry about stale data being
 134     // used.
 135     void
 136     invalidate()
 137     {
 138         invalidationCallbacks->process();
 139         // Delete and recreate the callback queue to ensure the callback
 140         // objects are deleted.
 141         invalidationCallbacks.reset(new CallbackQueue());
 142     }
 143
 144   private:
 145     std::unique_ptr<CallbackQueue> invalidationCallbacks;
 146
 147     AddrRange _range;
 148     uint8_t *_ptr;
 149     Flags _flags;
 150 };
 151
 152 typedef MemBackdoor *MemBackdoorPtr;
 153
 154 #endif  //__MEM_BACKDOOR_HH__