197 lines
5.2 KiB
HTML
197 lines
5.2 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of SUBPAGE_PROT</TITLE>
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</HEAD><BODY>
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<H1>SUBPAGE_PROT</H1>
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Section: Linux Programmer's Manual (2)<BR>Updated: 2019-03-06<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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subpage_prot - define a subpage protection for an address range
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>long subpage_prot(unsigned long </B><I>addr</I><B>, unsigned long </B><I>len</I><B>,</B>
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<B> uint32_t *</B><I>map</I><B>);</B>
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</PRE>
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<P>
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<I>Note</I>:
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There is no glibc wrapper for this system call; see NOTES.
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The PowerPC-specific
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<B>subpage_prot</B>()
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system call provides the facility to control the access
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permissions on individual 4 kB subpages on systems configured with
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a page size of 64 kB.
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<P>
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The protection map is applied to the memory pages in the region starting at
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<I>addr</I>
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and continuing for
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<I>len</I>
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bytes.
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Both of these arguments must be aligned to a 64-kB boundary.
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<P>
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The protection map is specified in the buffer pointed to by
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<I>map</I>.
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The map has 2 bits per 4 kB subpage;
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thus each 32-bit word specifies the protections of 16 4 kB subpages
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inside a 64 kB page
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(so, the number of 32-bit words pointed to by
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<I>map</I>
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should equate to the number of 64-kB pages specified by
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<I>len</I>).
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Each 2-bit field in the protection map is either 0 to allow any access,
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1 to prevent writes, or 2 or 3 to prevent all accesses.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success,
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<B>subpage_prot</B>()
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returns 0.
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Otherwise, one of the error codes specified below is returned.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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<DL COMPACT>
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<DT id="1"><B>EFAULT</B>
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<DD>
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The buffer referred to by
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<I>map</I>
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is not accessible.
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<DT id="2"><B>EINVAL</B>
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<DD>
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The
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<I>addr</I>
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or
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<I>len</I>
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arguments are incorrect.
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Both of these arguments must be aligned to a multiple of the system page size,
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and they must not refer to a region outside of the
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address space of the process or to a region that consists of huge pages.
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<DT id="3"><B>ENOMEM</B>
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<DD>
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Out of memory.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>VERSIONS</H2>
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This system call is provided on the PowerPC architecture
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since Linux 2.6.25.
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The system call is provided only if the kernel is configured with
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<B>CONFIG_PPC_64K_PAGES</B>.
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No library support is provided.
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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This system call is Linux-specific.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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Glibc does not provide a wrapper for this system call; call it using
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<B><A HREF="/cgi-bin/man/man2html?2+syscall">syscall</A></B>(2).
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<P>
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Normal page protections (at the 64-kB page level) also apply;
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the subpage protection mechanism is an additional constraint,
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so putting 0 in a 2-bit field won't allow writes to a page that is otherwise
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write-protected.
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<A NAME="lbAJ"> </A>
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<H3>Rationale</H3>
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This system call is provided to assist writing emulators that
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operate using 64-kB pages on PowerPC systems.
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When emulating systems such as x86, which uses a smaller page size,
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the emulator can no longer use the memory-management unit (MMU)
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and normal system calls for controlling page protections.
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(The emulator could emulate the MMU by checking and possibly remapping
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the address for each memory access in software, but that is slow.)
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The idea is that the emulator supplies an array of protection masks
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to apply to a specified range of virtual addresses.
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These masks are applied at the level where hardware page-table entries (PTEs)
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are inserted into the hardware page table based on the Linux PTEs,
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so the Linux PTEs are not affected.
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Implicit in this is that the regions of the address space that are
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protected are switched to use 4-kB hardware pages rather than 64-kB
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hardware pages (on machines with hardware 64-kB page support).
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<A NAME="lbAK"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?2+mprotect">mprotect</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+syscall">syscall</A></B>(2)
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<P>
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<I>Documentation/admin-guide/mm/hugetlbpage.rst</I>
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in the Linux kernel source tree
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<A NAME="lbAL"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="4"><A HREF="#lbAB">NAME</A><DD>
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<DT id="5"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="6"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="7"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="8"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="9"><A HREF="#lbAG">VERSIONS</A><DD>
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<DT id="10"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="11"><A HREF="#lbAI">NOTES</A><DD>
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<DL>
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<DT id="12"><A HREF="#lbAJ">Rationale</A><DD>
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</DL>
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<DT id="13"><A HREF="#lbAK">SEE ALSO</A><DD>
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<DT id="14"><A HREF="#lbAL">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:34 GMT, March 31, 2021
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