I'm currently working with windows kernel driver that allocate memory which should be shared with a program.

Afaik an application can ask the driver to create a memory buffer of max 4G size for windows 10. The driver then create this buffer in KernelSpace with MmAllocatePagesForMdl, and then map this buffer in User mode with MmMapLockedPagesSpecifyCache. The resulting pointer is given back to the application which can directly write in it like in any ordinary buffer. I attempt to make this in order to share my kernel buffer with the application. As first step I allocate an mdl:

        KdPrint((" STEP 1 IoAllocateMdl !!!! \n"));

        deviceExtension->mainDmaWriteBufferMdl = IoAllocateMdl(
            (PVOID)((ULONG_PTR)deviceExtension->DMA.CommonBuffer),// 
            MAX_Buf_Size,   // Size is 1G
            FALSE,  // No IRP associated
            FALSE, //TRUE,  // Top driver 
            NULL);   // Associated IRP not specified

then map this buffer in User mode

            KdPrint((" STEP 2 MmBuildMdlForNonPagedPool !!!! \n"));
            MmBuildMdlForNonPagedPool(deviceExtension->mainDmaWriteBufferMdl);

KdPrint((" STEP 3 MmMapLockedPagesSpecifyCache !!!! \n"));

                if (deviceExtension->mainDmaWriteBufferMdl->MdlFlags & (MDL_MAPPED_TO_SYSTEM_VA | MDL_SOURCE_IS_NONPAGED_POOL))
                {
                    KdPrint(("WDM 1.0  !!!! \n"));
                    deviceExtension->userSpaceMainDmaWriteBuffer = deviceExtension->mainDmaWriteBufferMdl->MappedSystemVa;
                }
                else
                {
                    deviceExtension->userSpaceMainDmaWriteBuffer = MmMapLockedPagesSpecifyCache(
                        deviceExtension->mainDmaWriteBufferMdl,
                        KernelMode,    //UserMode,   //
                        MmNonCached,
                        NULL,               // No user space address specified (system choose it)
                        FALSE,
                        NormalPagePriority | MdlMappingNoWrite | MdlMappingNoExecute);
                }

The application should only read from buffer. All seems to be ok, and I receive a deviceExtension->userSpaceMainDmaWriteBuffer different from null that i return to main appilcation. But when I attempt to read from this pointer I receive an exception. This is the log from DebugView:

STEP 1 IoAllocateMdl !!!!

Main DMA: Common Write Buffer MDL: FFFF850F3B010000

STEP 2 MmBuildMdlForNonPagedPool !!!!

STEP 3 MmMapLockedPagesSpecifyCache !!!!

WDM 1.0 !!!!

Main DMA: DMA Write Buffer mapped in user space at FFFFD77400000000 (2)

[3132] MapMemorySpace : DeviceIOControl ok, address 0xffffd77400000000

No changes if in step 3 I force call to MmMapLockedPagesSpecifyCache, that is:

KdPrint((" STEP 3 MmMapLockedPagesSpecifyCache !!!! \n"));

                    deviceExtension->userSpaceMainDmaWriteBuffer = MmMapLockedPagesSpecifyCache(
                        deviceExtension->mainDmaWriteBufferMdl,
                        KernelMode,    //UserMode,   //
                        MmNonCached,
                        NULL,               // No user space address specified (system choose it)
                        FALSE,
                        NormalPagePriority | MdlMappingNoWrite | MdlMappingNoExecute);

Where I am going wrong ? Anyone can explain ?