subpage_prot — define a subpage protection for an address range
||unsigned long addr,|
|unsigned long len,|
|There is no glibc wrapper for this system call; see NOTES.|
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
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.
returns 0. Otherwise, one of the error codes specified below
The buffer referred to by
map is not
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
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
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 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).
This page is part of release 4.07 of the Linux
man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
Copyright (c) 2010 Michael Kerrisk <mtk.manpagesgmail.com>
based on a proposal from Stephan Mueller <smuelleratsec.com>
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Formatted or processed versions of this manual, if unaccompanied by
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Various pieces of text taken from the kernel source and the commentary
in kernel commit fa28237cfcc5827553044cbd6ee52e33692b0faa
both written by Paul Mackerras <paulussamba.org>