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    The following form allows you to view linux man pages.

    Command:

    subpage_prot

    
    
    

    SYNOPSIS

           long subpage_prot(unsigned long addr, unsigned long len,
                             uint32_t *map);
    
           Note: There is no glibc wrapper for this system call; see NOTES.
    
    
    

    DESCRIPTION

           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.
    
    
    

    RETURN VALUE

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

    ERRORS

           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.
    
    
    

    VERSIONS

           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.
    
    
    

    CONFORMING TO

           This system call is Linux-specific.
    
    
    

    NOTES

           Glibc  does  not  provide a wrapper for this system call; call it using
           syscall(2).
    
           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-
           regions of the address space that are protected  are  switched  to  use
           4-kB  hardware pages rather than 64-kB hardware pages (on machines with
           hardware 64-kB page support).
    
    
    

    SEE ALSO

           mprotect(2), syscall(2)
    
           Documentation/vm/hugetlbpage.txt in the Linux kernel source tree
    
    
    

    Linux 2012-07-13 SUBPAGE_PROT(2)

    
    
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