observe physical address content - linux

Question

I compile and run the pagemap_dump.c from here :
/proc/[pid]/pagemaps and /proc/[pid]/maps | linux
and another application attach a exist shared memory and every time I run pagemap_dump , the shared memory's physical address is really the same (virtual memory address is different each time I observe) :
./pagemap_dump.exe 2135 <== 2135 is pid
./pagemap_dump.exe 5864 <== 5864 is pid
./pagemap_dump.exe 5110 <== 5110 is pid
the output :
7fabb37e1000 54edde 0 1 0 1 /dev/shm/memtest.shared
7f0040fa1000 54edde 0 1 0 1 /dev/shm/memtest.shared
7ffbd2869000 54edde 0 1 0 1 /dev/shm/memtest.shared
these 3 application attach memtest.shared and their physical address are all 0x54edde in my linux ,
then I try to access the contents from /dev/mem in this
physical address :
How to access physical addresses from user space in Linux?
int main(int argc, char** argv)
{
if (argc < 3) {
printf("Usage: %s <phys_addr> <offset>\n", argv[0]);
return 0;
}
off_t offset = strtoul(argv[1], NULL, 0);
size_t len = strtoul(argv[2], NULL, 0);
// Truncate offset to a multiple of the page size, or mmap will fail.
size_t pagesize = sysconf(_SC_PAGE_SIZE);
off_t page_base = (offset / pagesize) * pagesize;
off_t page_offset = offset - page_base;
int fd = open("/dev/mem", O_RDONLY|O_SYNC);
unsigned char *mem = (unsigned char *) mmap(NULL, page_offset + len, PROT_READ , MAP_SHARED, fd, page_base);
if (mem == MAP_FAILED) {
perror("Can't map memory");
return -1;
}
size_t i;
for (i = 0; i < len; ++i)
printf("%02x ", (int)mem[page_offset + i]);
return 0;
} // main
chown root testz1.exe
chmod 4775 testz1.exe
./testz1.exe 5565918 16 <=== 0x54edde = 5565918
I got Can't map memory: Operation not permitted
./testz1.exe 54edde 16
I got some thing not like "hello world" what I strcpy to
/dev/shm/memtest.shared when I create it .
Since I seems to get the physical address of /dev/shm/memtest.shared , how can I get the right way to get the contents from /dev/mem of this physical address ?!
Edit :
After download devmem2.c and run :
./devmem2.exe 0x54edde w
get the following message :
/dev/mem opened.
Error at line 75, file devmem2.c (1) [Operation not permitted]
Look like 0x54edde is not a physical address as I expect , but Why it happened?!
pagemap_dump.c really show the physical address of /dev/shm/memtest.shared
for all processes which attach it the value 0x54edde , then Why
devmem2.c can not access it right ?!