long subpage_prot(unsigned long addr, unsigned long len,
                         uint32_t *map);

       The  PowerPC-specific  subpage_prot() system call provides the facility
       to control the access permissions on individual 4kB subpages on systems
       configured with a page size of 64kB.

       The  protection map is applied to the memory pages in the region start-
       ing at addr and continuing for len bytes.  Both of these arguments must
       be aligned to a 64-kB boundary.

       The  protection  map is specified in the buffer pointed to by map.  The
       map has 2 bits per 4kB subpage; thus each  32-bit  word  specifies  the
       protections  of  16  4kB subpages inside a 64kB page (so, the number of
       32-bit words pointed to by map should equate to  the  number  of  64-kB
       pages  specified  by  len).   Each 2-bit field in the protection map is
       either 0 to allow any access, 1 to prevent writes, or 2 or 3 to prevent
       all accesses.

       On  success,  subpage_prot()  returns  0.   Otherwise, one of the error
       codes specified below is returned.

       EFAULT The buffer referred to by map is not accessible.

       EINVAL The addr or len arguments are incorrect.  Both  of  these  argu-
              ments must be aligned to a multiple of the system page size, and
              they must not refer to a region outside of the address space  of
              the process or to a region that consists of huge pages.

       ENOMEM Out of memory.

       This  system  call  is provided on the PowerPC architecture since Linux
       2.6.25.  The system call is provided only if the kernel  is  configured
       with CONFIG_PPC_64K_PAGES.  No library support is provided.

       This system call is Linux-specific.

       Normal  page protections (at the 64-kB page level) also apply; the sub-
       page protection mechanism is an additional constraint, so putting 0  in
       a 2-bit field won't allow writes to a page that is otherwise write-pro-

       This system call is provided to assist writing emulators  that  operate
       using  64-kB  pages on PowerPC systems.  When emulating systems such as
       x86, which uses a smaller page size, the emulator can no longer use the

       mprotect(2), syscall(2);
       the kernel source file Documentation/vm/hugetlbpage.txt.

       This  page  is  part of release 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

Linux                             2010-10-30                   SUBPAGE_PROT(2)
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