DX12: PageGuardManager may fail to track pages of overlapping placed resources

[davidd-lunarg]

When memory is mapped in DX12, its pointer is used as the identifier for the memory.

In D3D12CaptureManager::PostProcess_ID3D12Resource_Map:
manager->AddTrackedMemory(reinterpret_cast<uint64_t>(mapped_subresource.data),

In PageGuardManager::AddTrackedMemory:

auto entry =
    memory_info_.emplace(std::piecewise_construct,
                     std::forward_as_tuple(memory_id),
                     std::forward_as_tuple(mapped_memory,
                                           mapped_range,
                                           shadow_memory,
                                           shadow_size,
                                           aligned_address,
                                           aligned_offset,
                                           total_pages,
                                           last_segment_size,
                                           start_address,
                                           static_cast<const uint8_t*>(start_address) + mapped_range,
                                           use_write_watch,
                                           shadow_memory_handle == kNullShadowHandle));

If two overlapping resources are created and mapped at the same resource (with CreatePlacedResource), the second call to AddTrackedMemory does not update the memory_info_ map. And if the second resource mapped is larger than the first resource, the additional memory pages it covers won't be processed in PageGuardManager::LoadActiveWriteStates because the dirty pages are retrieved based on the information stored in the memory_info_ map:

    if (GetWriteWatch(WRITE_WATCH_FLAG_RESET,
                      memory_info->aligned_address,
                      memory_info->mapped_range + memory_info->aligned_offset,
                      modified_addresses,
                      &modified_count,
                      &granularity) == 0)

This is a potential issue identified by code inspection. I am not aware of a real world use case that encounters this problem.