diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/00-INDEX | 6 | ||||
| -rw-r--r-- | Documentation/DocBook/Makefile | 2 | ||||
| -rw-r--r-- | Documentation/DocBook/kgdb.tmpl | 447 | ||||
| -rw-r--r-- | Documentation/feature-removal-schedule.txt | 2 | ||||
| -rw-r--r-- | Documentation/i386/boot.txt | 28 | ||||
| -rw-r--r-- | Documentation/kernel-parameters.txt | 23 | ||||
| -rw-r--r-- | Documentation/s390/s390dbf.txt | 21 | ||||
| -rw-r--r-- | Documentation/timers/highres.txt (renamed from Documentation/hrtimers/highres.txt) | 0 | ||||
| -rw-r--r-- | Documentation/timers/hrtimers.txt (renamed from Documentation/hrtimers/hrtimers.txt) | 0 | ||||
| -rw-r--r-- | Documentation/timers/timer_stats.txt (renamed from Documentation/hrtimer/timer_stats.txt) | 0 | ||||
| -rw-r--r-- | Documentation/x86/pat.txt | 100 | ||||
| -rw-r--r-- | Documentation/x86_64/boot-options.txt | 5 |
12 files changed, 628 insertions, 6 deletions
diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX index e8fb2467196..f7923a42e76 100644 --- a/Documentation/00-INDEX +++ b/Documentation/00-INDEX @@ -167,10 +167,8 @@ highuid.txt - notes on the change from 16 bit to 32 bit user/group IDs. hpet.txt - High Precision Event Timer Driver for Linux. -hrtimer/ - - info on the timer_stats debugging facility for timer (ab)use. -hrtimers/ - - info on the hrtimers subsystem for high-resolution kernel timers. +timers/ + - info on the timer related topics hw_random.txt - info on Linux support for random number generator in i8xx chipsets. hwmon/ diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index 300e1707893..e471bc466a7 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -9,7 +9,7 @@ DOCBOOKS := wanbook.xml z8530book.xml mcabook.xml videobook.xml \ kernel-hacking.xml kernel-locking.xml deviceiobook.xml \ procfs-guide.xml writing_usb_driver.xml networking.xml \ - kernel-api.xml filesystems.xml lsm.xml usb.xml \ + kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml \ gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \ genericirq.xml s390-drivers.xml uio-howto.xml scsi.xml diff --git a/Documentation/DocBook/kgdb.tmpl b/Documentation/DocBook/kgdb.tmpl new file mode 100644 index 00000000000..97618bed4d6 --- /dev/null +++ b/Documentation/DocBook/kgdb.tmpl @@ -0,0 +1,447 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="kgdbOnLinux"> + <bookinfo> + <title>Using kgdb and the kgdb Internals</title> + + <authorgroup> + <author> + <firstname>Jason</firstname> + <surname>Wessel</surname> + <affiliation> + <address> + <email>jason.wessel@windriver.com</email> + </address> + </affiliation> + </author> + </authorgroup> + + <authorgroup> + <author> + <firstname>Tom</firstname> + <surname>Rini</surname> + <affiliation> + <address> + <email>trini@kernel.crashing.org</email> + </address> + </affiliation> + </author> + </authorgroup> + + <authorgroup> + <author> + <firstname>Amit S.</firstname> + <surname>Kale</surname> + <affiliation> + <address> + <email>amitkale@linsyssoft.com</email> + </address> + </affiliation> + </author> + </authorgroup> + + <copyright> + <year>2008</year> + <holder>Wind River Systems, Inc.</holder> + </copyright> + <copyright> + <year>2004-2005</year> + <holder>MontaVista Software, Inc.</holder> + </copyright> + <copyright> + <year>2004</year> + <holder>Amit S. Kale</holder> + </copyright> + + <legalnotice> + <para> + This file is licensed under the terms of the GNU General Public License + version 2. This program is licensed "as is" without any warranty of any + kind, whether express or implied. + </para> + + </legalnotice> + </bookinfo> + +<toc></toc> + <chapter id="Introduction"> + <title>Introduction</title> + <para> + kgdb is a source level debugger for linux kernel. It is used along + with gdb to debug a linux kernel. The expectation is that gdb can + be used to "break in" to the kernel to inspect memory, variables + and look through a cal stack information similar to what an + application developer would use gdb for. It is possible to place + breakpoints in kernel code and perform some limited execution + stepping. + </para> + <para> + Two machines are required for using kgdb. One of these machines is a + development machine and the other is a test machine. The kernel + to be debugged runs on the test machine. The development machine + runs an instance of gdb against the vmlinux file which contains + the symbols (not boot image such as bzImage, zImage, uImage...). + In gdb the developer specifies the connection parameters and + connects to kgdb. Depending on which kgdb I/O modules exist in + the kernel for a given architecture, it may be possible to debug + the test machine's kernel with the development machine using a + rs232 or ethernet connection. + </para> + </chapter> + <chapter id="CompilingAKernel"> + <title>Compiling a kernel</title> + <para> + To enable <symbol>CONFIG_KGDB</symbol>, look under the "Kernel debugging" + and then select "KGDB: kernel debugging with remote gdb". + </para> + <para> + Next you should choose one of more I/O drivers to interconnect debugging + host and debugged target. Early boot debugging requires a KGDB + I/O driver that supports early debugging and the driver must be + built into the kernel directly. Kgdb I/O driver configuration + takes place via kernel or module parameters, see following + chapter. + </para> + <para> + The kgdb test compile options are described in the kgdb test suite chapter. + </para> + + </chapter> + <chapter id="EnableKGDB"> + <title>Enable kgdb for debugging</title> + <para> + In order to use kgdb you must activate it by passing configuration + information to one of the kgdb I/O drivers. If you do not pass any + configuration information kgdb will not do anything at all. Kgdb + will only actively hook up to the kernel trap hooks if a kgdb I/O + driver is loaded and configured. If you unconfigure a kgdb I/O + driver, kgdb will unregister all the kernel hook points. + </para> + <para> + All drivers can be reconfigured at run time, if + <symbol>CONFIG_SYSFS</symbol> and <symbol>CONFIG_MODULES</symbol> + are enabled, by echo'ing a new config string to + <constant>/sys/module/<driver>/parameter/<option></constant>. + The driver can be unconfigured by passing an empty string. You cannot + change the configuration while the debugger is attached. Make sure + to detach the debugger with the <constant>detach</constant> command + prior to trying unconfigure a kgdb I/O driver. + </para> + <sect1 id="kgdbwait"> + <title>Kernel parameter: kgdbwait</title> + <para> + The Kernel command line option <constant>kgdbwait</constant> makes + kgdb wait for a debugger connection during booting of a kernel. You + can only use this option you compiled a kgdb I/O driver into the + kernel and you specified the I/O driver configuration as a kernel + command line option. The kgdbwait parameter should always follow the + configuration parameter for the kgdb I/O driver in the kernel + command line else the I/O driver will not be configured prior to + asking the kernel to use it to wait. + </para> + <para> + The kernel will stop and wait as early as the I/O driver and + architecture will allow when you use this option. If you build the + kgdb I/O driver as a kernel module kgdbwait will not do anything. + </para> + </sect1> + <sect1 id="kgdboc"> + <title>Kernel parameter: kgdboc</title> + <para> + The kgdboc driver was originally an abbreviation meant to stand for + "kgdb over console". Kgdboc is designed to work with a single + serial port. It was meant to cover the circumstance + where you wanted to use a serial console as your primary console as + well as using it to perform kernel debugging. Of course you can + also use kgdboc without assigning a console to the same port. + </para> + <sect2 id="UsingKgdboc"> + <title>Using kgdboc</title> + <para> + You can configure kgdboc via sysfs or a module or kernel boot line + parameter depending on if you build with CONFIG_KGDBOC as a module + or built-in. + <orderedlist> + <listitem><para>From the module load or build-in</para> + <para><constant>kgdboc=<tty-device>,[baud]</constant></para> + <para> + The example here would be if your console port was typically ttyS0, you would use something like <constant>kgdboc=ttyS0,115200</constant> or on the ARM Versatile AB you would likely use <constant>kgdboc=ttyAMA0,115200</constant> + </para> + </listitem> + <listitem><para>From sysfs</para> + <para><constant>echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc</constant></para> + </listitem> + </orderedlist> + </para> + <para> + NOTE: Kgdboc does not support interrupting the target via the + gdb remote protocol. You must manually send a sysrq-g unless you + have a proxy that splits console output to a terminal problem and + has a separate port for the debugger to connect to that sends the + sysrq-g for you. + </para> + <para>When using kgdboc with no debugger proxy, you can end up + connecting the debugger for one of two entry points. If an + exception occurs after you have loaded kgdboc a message should print + on the console stating it is waiting for the debugger. In case you + disconnect your terminal program and then connect the debugger in + its place. If you want to interrupt the target system and forcibly + enter a debug session you have to issue a Sysrq sequence and then + type the letter <constant>g</constant>. Then you disconnect the + terminal session and connect gdb. Your options if you don't like + this are to hack gdb to send the sysrq-g for you as well as on the + initial connect, or to use a debugger proxy that allows an + unmodified gdb to do the debugging. + </para> + </sect2> + </sect1> + <sect1 id="kgdbcon"> + <title>Kernel parameter: kgdbcon</title> + <para> + Kgdb supports using the gdb serial protocol to send console messages + to the debugger when the debugger is connected and running. There + are two ways to activate this feature. + <orderedlist> + <listitem><para>Activate with the kernel command line option:</para> + <para><constant>kgdbcon</constant></para> + </listitem> + <listitem><para>Use sysfs before configuring an io driver</para> + <para> + <constant>echo 1 > /sys/module/kgdb/parameters/kgdb_use_con</constant> + </para> + <para> + NOTE: If you do this after you configure the kgdb I/O driver, the + setting will not take effect until the next point the I/O is + reconfigured. + </para> + </listitem> + </orderedlist> + </para> + <para> + IMPORTANT NOTE: Using this option with kgdb over the console + (kgdboc) or kgdb over ethernet (kgdboe) is not supported. + </para> + </sect1> + </chapter> + <chapter id="ConnectingGDB"> + <title>Connecting gdb</title> + <para> + If you are using kgdboc, you need to have used kgdbwait as a boot + argument, issued a sysrq-g, or the system you are going to debug + has already taken an exception and is waiting for the debugger to + attach before you can connect gdb. + </para> + <para> + If you are not using different kgdb I/O driver other than kgdboc, + you should be able to connect and the target will automatically + respond. + </para> + <para> + Example (using a serial port): + </para> + <programlisting> + % gdb ./vmlinux + (gdb) set remotebaud 115200 + (gdb) target remote /dev/ttyS0 + </programlisting> + <para> + Example (kgdb to a terminal server): + </para> + <programlisting> + % gdb ./vmlinux + (gdb) target remote udp:192.168.2.2:6443 + </programlisting> + <para> + Example (kgdb over ethernet): + </para> + <programlisting> + % gdb ./vmlinux + (gdb) target remote udp:192.168.2.2:6443 + </programlisting> + <para> + Once connected, you can debug a kernel the way you would debug an + application program. + </para> + <para> + If you are having problems connecting or something is going + seriously wrong while debugging, it will most often be the case + that you want to enable gdb to be verbose about its target + communications. You do this prior to issuing the <constant>target + remote</constant> command by typing in: <constant>set remote debug 1</constant> + </para> + </chapter> + <chapter id="KGDBTestSuite"> + <title>kgdb Test Suite</title> + <para> + When kgdb is enabled in the kernel config you can also elect to + enable the config parameter KGDB_TESTS. Turning this on will + enable a special kgdb I/O module which is designed to test the + kgdb internal functions. + </para> + <para> + The kgdb tests are mainly intended for developers to test the kgdb + internals as well as a tool for developing a new kgdb architecture + specific implementation. These tests are not really for end users + of the Linux kernel. The primary source of documentation would be + to look in the drivers/misc/kgdbts.c file. + </para> + <para> + The kgdb test suite can also be configured at compile time to run + the core set of tests by setting the kernel config parameter + KGDB_TESTS_ON_BOOT. This particular option is aimed at automated + regression testing and does not require modifying the kernel boot + config arguments. If this is turned on, the kgdb test suite can + be disabled by specifying "kgdbts=" as a kernel boot argument. + </para> + </chapter> + <chapter id="CommonBackEndReq"> + <title>KGDB Internals</title> + <sect1 id="kgdbArchitecture"> + <title>Architecture Specifics</title> + <para> + Kgdb is organized into three basic components: + <orderedlist> + <listitem><para>kgdb core</para> + <para> + The kgdb core is found in kernel/kgdb.c. It contains: + <itemizedlist> + <listitem><para>All the logic to implement the gdb serial protocol</para></listitem> + <listitem><para>A generic OS exception handler which includes sync'ing the processors into a stopped state on an multi cpu system.</para></listitem> + <listitem><para>The API to talk to the kgdb I/O drivers</para></listitem> + <listitem><para>The API to make calls to the arch specific kgdb implementation</para></listitem> + <listitem><para>The logic to perform safe memory reads and writes to memory while using the debugger</para></listitem> + <listitem><para>A full implementation for software breakpoints unless overridden by the arch</para></listitem> + </itemizedlist> + </para> + </listitem> + <listitem><para>kgdb arch specific implementation</para> + <para> + This implementation is generally found in arch/*/kernel/kgdb.c. + As an example, arch/x86/kernel/kgdb.c contains the specifics to + implement HW breakpoint as well as the initialization to + dynamically register and unregister for the trap handlers on + this architecture. The arch specific portion implements: + <itemizedlist> + <listitem><para>contains an arch specific trap catcher which + invokes kgdb_handle_exception() to start kgdb about doing its + work</para></listitem> + <listitem><para>translation to and from gdb specific packet format to pt_regs</para></listitem> + <listitem><para>Registration and unregistration of architecture specific trap hooks</para></listitem> + <listitem><para>Any special exception handling and cleanup</para></listitem> + <listitem><para>NMI exception handling and cleanup</para></listitem> + <listitem><para>(optional)HW breakpoints</para></listitem> + </itemizedlist> + </para> + </listitem> + <listitem><para>kgdb I/O driver</para> + <para> + Each kgdb I/O driver has to provide an implemenation for the following: + <itemizedlist> + <listitem><para>configuration via builtin or module</para></listitem> + <listitem><para>dynamic configuration and kgdb hook registration calls</para></listitem> + <listitem><para>read and write character interface</para></listitem> + <listitem><para>A cleanup handler for unconfiguring from the kgdb core</para></listitem> + <listitem><para>(optional) Early debug methodology</para></listitem> + </itemizedlist> + Any given kgdb I/O driver has to operate very closely with the + hardware and must do it in such a way that does not enable + interrupts or change other parts of the system context without + completely restoring them. The kgdb core will repeatedly "poll" + a kgdb I/O driver for characters when it needs input. The I/O + driver is expected to return immediately if there is no data + available. Doing so allows for the future possibility to touch + watch dog hardware in such a way as to have a target system not + reset when these are enabled. + </para> + </listitem> + </orderedlist> + </para> + <para> + If you are intent on adding kgdb architecture specific support + for a new architecture, the architecture should define + <constant>HAVE_ARCH_KGDB</constant> in the architecture specific + Kconfig file. This will enable kgdb for the architecture, and + at that point you must create an architecture specific kgdb + implementation. + </para> + <para> + There are a few flags which must be set on every architecture in + their <asm/kgdb.h> file. These are: + <itemizedlist> + <listitem> + <para> + NUMREGBYTES: The size in bytes of all of the registers, so + that we can ensure they will all fit into a packet. + </para> + <para> + BUFMAX: The size in bytes of the buffer GDB will read into. + This must be larger than NUMREGBYTES. + </para> + <para> + CACHE_FLUSH_IS_SAFE: Set to 1 if it is always safe to call + flush_cache_range or flush_icache_range. On some architectures, + these functions may not be safe to call on SMP since we keep other + CPUs in a holding pattern. + </para> + </listitem> + </itemizedlist> + </para> + <para> + There are also the following functions for the common backend, + found in kernel/kgdb.c, that must be supplied by the + architecture-specific backend unless marked as (optional), in + which case a default function maybe used if the architecture + does not need to provide a specific implementation. + </para> +!Iinclude/linux/kgdb.h + </sect1> + <sect1 id="kgdbocDesign"> + <title>kgdboc internals</title> + <para> + The kgdboc driver is actually a very thin driver that relies on the + underlying low level to the hardware driver having "polling hooks" + which the to which the tty driver is attached. In the initial + implementation of kgdboc it the serial_core was changed to expose a + low level uart hook for doing polled mode reading and writing of a + single character while in an atomic context. When kgdb makes an I/O + request to the debugger, kgdboc invokes a call back in the serial + core which in turn uses the call back in the uart driver. It is + certainly possible to extend kgdboc to work with non-uart based + consoles in the future. + </para> + <para> + When using kgdboc with a uart, the uart driver must implement two callbacks in the <constant>struct uart_ops</constant>. Example from drivers/8250.c:<programlisting> +#ifdef CONFIG_CONSOLE_POLL + .poll_get_char = serial8250_get_poll_char, + .poll_put_char = serial8250_put_poll_char, +#endif + </programlisting> + Any implementation specifics around creating a polling driver use the + <constant>#ifdef CONFIG_CONSOLE_POLL</constant>, as shown above. + Keep in mind that polling hooks have to be implemented in such a way + that they can be called from an atomic context and have to restore + the state of the uart chip on return such that the system can return + to normal when the debugger detaches. You need to be very careful + with any kind of lock you consider, because failing here is most + going to mean pressing the reset button. + </para> + </sect1> + </chapter> + <chapter id="credits"> + <title>Credits</title> + <para> + The following people have contributed to this document: + <orderedlist> + <listitem><para>Amit Kale<email>amitkale@linsyssoft.com</email></para></listitem> + <listitem><para>Tom Rini<email>trini@kernel.crashing.org</email></para></listitem> + </orderedlist> + In March 2008 this document was completely rewritten by: + <itemizedlist> + <listitem><para>Jason Wessel<email>jason.wessel@windriver.com</email></para></listitem> + </itemizedlist> + </para> + </chapter> +</book> + diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt index bf0e3df8e7a..164c89394cf 100644 --- a/Documentation/feature-removal-schedule.txt +++ b/Documentation/feature-removal-schedule.txt @@ -212,7 +212,7 @@ Who: Stephen Hemminger <shemminger@linux-foundation.org> --------------------------- What: i386/x86_64 bzImage symlinks -When: April 2008 +When: April 2010 Why: The i386/x86_64 merge provides a symlink to the old bzImage location so not yet updated user space tools, e.g. package diff --git a/Documentation/i386/boot.txt b/Documentation/i386/boot.txt index fc49b79bc1a..2eb16100bb3 100644 --- a/Documentation/i386/boot.txt +++ b/Documentation/i386/boot.txt @@ -170,6 +170,8 @@ Offset Proto Name Meaning 0238/4 2.06+ cmdline_size Maximum size of the kernel command line 023C/4 2.07+ hardware_subarch Hardware subarchitecture 0240/8 2.07+ hardware_subarch_data Subarchitecture-specific data +0248/4 2.08+ payload_offset Offset of kernel payload +024C/4 2.08+ payload_length Length of kernel payload (1) For backwards compatibility, if the setup_sects field contains 0, the real value is 4. @@ -512,6 +514,32 @@ Protocol: 2.07+ A pointer to data that is specific to hardware subarch +Field name: payload_offset +Type: read +Offset/size: 0x248/4 +Protocol: 2.08+ + + If non-zero then this field contains the offset from the end of the + real-mode code to the payload. + + The payload may be compressed. The format of both the compressed and + uncompressed data should be determined using the standard magic + numbers. Currently only gzip compressed ELF is used. + +Field name: payload_length +Type: read +Offset/size: 0x24c/4 +Protocol: 2.08+ + + The length of the payload. + +**** THE IMAGE CHECKSUM + +From boot protocol version 2.08 onwards the CRC-32 is calculated over +the entire file using the characteristic polynomial 0x04C11DB7 and an +initial remainder of 0xffffffff. The checksum is appended to the +file; therefore the CRC of the file up to the limit specified in the +syssize field of the header is always 0. **** THE KERNEL COMMAND LINE diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 239e78a1fcd..cd6f464b919 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -812,6 +812,19 @@ and is between 256 and 4096 characters. It is defined in the file inttest= [IA64] + iommu= [x86] + off + force + noforce + biomerge + panic + nopanic + merge + nomerge + forcesac + soft + + intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option off Disable intel iommu driver. @@ -928,6 +941,11 @@ and is between 256 and 4096 characters. It is defined in the file kstack=N [X86-32,X86-64] Print N words from the kernel stack in oops dumps. + kgdboc= [HW] kgdb over consoles. + Requires a tty driver that supports console polling. + (only serial suported for now) + Format: <serial_device>[,baud] + l2cr= [PPC] lapic [X86-32,APIC] Enable the local APIC even if BIOS @@ -1134,6 +1152,11 @@ and is between 256 and 4096 characters. It is defined in the file or memmap=0x10000$0x18690000 + memtest= [KNL,X86_64] Enable memtest + Format: <integer> + range: 0,4 : pattern number + default : 0 <disable> + meye.*= [HW] Set MotionEye Camera parameters See Documentation/video4linux/meye.txt. diff --git a/Documentation/s390/s390dbf.txt b/Documentation/s390/s390dbf.txt index 0eb7c58916d..e0542097369 100644 --- a/Documentation/s390/s390dbf.txt +++ b/Documentation/s390/s390dbf.txt @@ -115,6 +115,27 @@ Return Value: Handle for generated debug area Description: Allocates memory for a debug log Must not be called within an interrupt handler +---------------------------------------------------------------------------- +debug_info_t *debug_register_mode(char *name, int pages, int nr_areas, + int buf_size, mode_t mode, uid_t uid, + gid_t gid); + +Parameter: name: Name of debug log (e.g. used for debugfs entry) + pages: Number of pages, which will be allocated per area + nr_areas: Number of debug areas + buf_size: Size of data area in each debug entry + mode: File mode for debugfs files. E.g. S_IRWXUGO + uid: User ID for debugfs files. Currently only 0 is + supported. + gid: Group ID for debugfs files. Currently only 0 is + supported. + +Return Value: Handle for generated debug area + NULL if register failed + +Description: Allocates memory for a debug log + Must not be called within an interrupt handler + --------------------------------------------------------------------------- void debug_unregister (debug_info_t * id); diff --git a/Documentation/hrtimers/highres.txt b/Documentation/timers/highres.txt index a73ecf5b4bd..a73ecf5b4bd 100644 --- a/Documentation/hrtimers/highres.txt +++ b/Documentation/timers/highres.txt diff --git a/Documentation/hrtimers/hrtimers.txt b/Documentation/timers/hrtimers.txt index ce31f65e12e..ce31f65e12e 100644 --- a/Documentation/hrtimers/hrtimers.txt +++ b/Documentation/timers/hrtimers.txt diff --git a/Documentation/hrtimer/timer_stats.txt b/Documentation/timers/timer_stats.txt index 20d368c5981..20d368c5981 100644 --- a/Documentation/hrtimer/timer_stats.txt +++ b/Documentation/timers/timer_stats.txt diff --git a/Documentation/x86/pat.txt b/Documentation/x86/pat.txt new file mode 100644 index 00000000000..17965f927c1 --- /dev/null +++ b/Documentation/x86/pat.txt @@ -0,0 +1,100 @@ + +PAT (Page Attribute Table) + +x86 Page Attribute Table (PAT) allows for setting the memory attribute at the +page level granularity. PAT is complementary to the MTRR settings which allows +for setting of memory types over physical address ranges. However, PAT is +more flexible than MTRR due to its capability to set attributes at page level +and also due to the fact that there are no hardware limitations on number of +such attribute settings allowed. Added flexibility comes with guidelines for +not having memory type aliasing for the same physical memory with multiple +virtual addresses. + +PAT allows for different types of memory attributes. The most commonly used +ones that will be supported at this time are Write-back, Uncached, +Write-combined and Uncached Minus. + +There are many different APIs in the kernel that allows setting of memory +attributes at the page level. In order to avoid aliasing, these interfaces +should be used thoughtfully. Below is a table of interfaces available, +their intended usage and their memory attribute relationships. Internally, +these APIs use a reserve_memtype()/free_memtype() interface on the physical +address range to avoid any aliasing. + + +------------------------------------------------------------------- +API | RAM | ACPI,... | Reserved/Holes | +-----------------------|----------|------------|------------------| + | | | | +ioremap | -- | UC | UC | + | | | | +ioremap_cache | -- | WB | WB | + | | | | +ioremap_nocache | -- | UC | UC | + | | | | +ioremap_wc | -- | -- | WC | + | | | | +set_memory_uc | UC | -- | -- | + set_memory_wb | | | | + | | | | +set_memory_wc | WC | -- | -- | + set_memory_wb | | | | + | | | | +pci sysfs resource | -- | -- | UC | + | | | | +pci sysfs resource_wc | -- | -- | WC | + is IORESOURCE_PREFETCH| | | | + | | | | +pci proc | -- | -- | UC | + !PCIIOC_WRITE_COMBINE | | | | + | | | | +pci proc | -- | -- | WC | + PCIIOC_WRITE_COMBINE | | | | + | | | | +/dev/mem | -- | UC | UC | + read-write | | | | + | | | | +/dev/mem | -- | UC | UC | + mmap SYNC flag | | | | + | | | | +/dev/mem | -- | WB/WC/UC | WB/WC/UC | + mmap !SYNC flag | |(from exist-| (from exist- | + and | | ing alias)| ing alias) | + any alias to this area| | | | + | | | | +/dev/mem | -- | WB | WB | + mmap !SYNC flag | | | | + no alias to this area | | | | + and | | | | + MTRR says WB | | | | + | | | | +/dev/mem | -- | -- | UC_MINUS | + mmap !SYNC flag | | | | + no alias to this area | | | | + and | | | | + MTRR says !WB | | | | + | | | | +------------------------------------------------------------------- + +Notes: + +-- in the above table mean "Not suggested usage for the API". Some of the --'s +are strictly enforced by the kernel. Some others are not really enforced +today, but may be enforced in future. + +For ioremap and pci access through /sys or /proc - The actual type returned +can be more restrictive, in case of any existing aliasing for that address. +For example: If there is an existing uncached mapping, a new ioremap_wc can +return uncached mapping in place of write-combine requested. + +set_memory_[uc|wc] and set_memory_wb should be used in pairs, where driver will +first make a region uc or wc and switch it back to wb after use. + +Over time writes to /proc/mtrr will be deprecated in favor of using PAT based +interfaces. Users writing to /proc/mtrr are suggested to use above interfaces. + +Drivers should use ioremap_[uc|wc] to access PCI BARs with [uc|wc] access +types. + +Drivers should use set_memory_[uc|wc] to set access type for RAM ranges. + diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt index 34abae4e944..b0c7b6c4abd 100644 --- a/Documentation/x86_64/boot-options.txt +++ b/Documentation/x86_64/boot-options.txt @@ -307,3 +307,8 @@ Debugging stuck (default) Miscellaneous + + nogbpages + Do not use GB pages for kernel direct mappings. + gbpages + Use GB pages for kernel direct mappings. |