long subpage_prot(unsigned long addr, unsigned long len,
Note: There is no glibc wrapper for this system call; see NOTES.
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
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.
Glibc does not provide a wrapper for this system call; call it using
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-
PTEs, so the Linux PTEs are not affected. Implicit in this is that the
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).
Documentation/vm/hugetlbpage.txt in the Linux kernel source tree
This page is part of release 3.54 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2012-07-13 SUBPAGE_PROT(2)
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