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TDA4VM: Cannot access memory at address 0xffff8aaeb000

Part Number: TDA4VM

hi TI expert,

     I can't access some virtual address when i use GDB to debug my code on TDA4VM platform. 

     first, i map a vximage which get from a objectArray

              status = vxMapImagePatch(obj.onScreenImage[0], &rect, 0, &map_id, &image_addr, &data_ptr, VX_WRITE_ONLY, VX_MEMORY_TYPE_HOST,VX_NOGAP_X);

     second, i set a breakpoint after vxMapImagePatch successful and run to this breakpoint, then i use print to show the data in the data_ptr, the whole operation as below:

               (gdb) p data_ptr
                        $7 = (vx_uint8 *) 0xffff8aaeb000 <error: Cannot access memory at address 0xffff8aaeb000>

               (gdb) p *0xffff8aaeb000
                       Cannot access memory at address 0xffff8aaeb000 

               (gdb) p *0xffff8c003000
                        $8 = 0

               (gdb) info proc map
                      process 2648
                      Mapped address spaces:

                      Start Addr End Addr Size Offset objfile

                      0x3f3000 0xaeb4000 0xaac1000 0x0 [heap]
                      0xffff89d6b000 0xffff8a1a3000 0x438000 0x0 /dmabuf:
                      0xffff8a1a3000 0xffff8a5db000 0x438000 0x0 /dmabuf:
                      0xffff8a5db000 0xffff8aa13000 0x438000 0x0 /dmabuf:
                      0xffff8aa13000 0xffff8aaeb000 0xd8000 0x0 /dmabuf:
                      0xffff8aaeb000 0xffff8af23000 0x438000 0x0 /dmabuf:
                      0xffff8af23000 0xffff8b35b000 0x438000 0x0 /dmabuf:
                      0xffff8b35b000 0xffff8b793000 0x438000 0x0 /dmabuf:
                      0xffff8b793000 0xffff8bbcb000 0x438000 0x0 /dmabuf:
                      0xffff8bbcb000 0xffff8c003000 0x438000 0x0 /dmabuf:
                      0xffff8c003000 0xffff8c013000 0x10000 0x0
                      0xffff8c013000 0xffff8c813000 0x800000 0x0
                      0xffff8c813000 0xffff8c823000 0x10000 0x0

                    according to my test, the virtual addr named dambuf  can't be accessed and others can be accessed, why ? waiting for your help, Thanks.