long subpage_prot(unsigned long addr, unsigned long len,
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.
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
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 http://man7.org/linux/man-pages/.
Linux 2010-10-30 SUBPAGE_PROT(2)
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