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SUBPAGE_PROT(2) Linux Programmer's Manual SUBPAGE_PROT(2)
subpage_prot - define a subpage protection for an address range
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 starting 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 arguments 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 subpage
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-protected.
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 memory-management
unit (MMU) and normal system calls for controlling page protections. (The
emulator could emulate the MMU by checking and possibly remapping the address
for each memory access in software, but that is slow.) The idea is that the
emulator supplies an array of protection masks to apply to a specified range
of virtual addresses. These masks are applied at the level where hardware
page-table entries (PTEs) are inserted into the hardware page table based on
the Linux 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).
syscall(2);
the kernel source file Documentation/vm/hugetlbpage.txt.
This page is part of release 3.32 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 2010-10-30 SUBPAGE_PROT(2)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface