Say yes to build a 64-bit kernel - formerly known as x86_64 Say no to build a 32-bit kernel - formerly known as i386
We keep the static function tracing (!DYNAMIC_FTRACE) around in order to test the non static function tracing in the generic code, as other architectures still use it. But we only need to keep it around for x86_64. No need to keep it for x86_32. For x86_32, force DYNAMIC_FTRACE.
We have to make sure stack protector is unconditionally disabled if the compiler produces broken code or if it does not let us control the segment on 32-bit kernels.
DMA memory allocation support allows devices with less than 32-bit addressing to allocate within the first 16MB of address space. Disable if no such devices will be used. If unsure, say Y.
This enables support for systems with more than one CPU. If you have a system with only one CPU, say N. If you have a system with more than one CPU, say Y. If you say N here, the kernel will run on uni- and multiprocessor machines, but will use only one CPU of a multiprocessor machine. If you say Y here, the kernel will run on many, but not all, uniprocessor machines. On a uniprocessor machine, the kernel will run faster if you say N here. Note that if you say Y here and choose architecture "586" or "Pentium" under "Processor family", the kernel will not work on 486 architectures. Similarly, multiprocessor kernels for the "PPro" architecture may not work on all Pentium based boards. People using multiprocessor machines who say Y here should also say Y to "Enhanced Real Time Clock Support", below. The "Advanced Power Management" code will be disabled if you say Y here. See also <file:Documentation/x86/i386/IO-APIC.rst>, <file:Documentation/admin-guide/lockup-watchdogs.rst> and the SMP-HOWTO available at <http://www.tldp.org/docs.html#howto>. If you don't know what to do here, say N.
This option compiles in a table of x86 feature bits and corresponding names. This is required to support /proc/cpuinfo and a few kernel messages. You can disable this to save space, at the expense of making those few kernel messages show numeric feature bits instead. If in doubt, say Y.
This enables x2apic support on CPUs that have this feature. This allows 32-bit apic IDs (so it can support very large systems), and accesses the local apic via MSRs not via mmio. If you don't know what to do here, say N.
For old smp systems that do not have proper acpi support. Newer systems (esp with 64bit cpus) with acpi support, MADT and DSDT will override it
Compile kernel with the retpoline compiler options to guard against kernel-to-user data leaks by avoiding speculative indirect branches. Requires a compiler with -mindirect-branch=thunk-extern support for full protection. The kernel may run slower.
Enable x86 CPU resource control support. Provide support for the allocation and monitoring of system resources usage by the CPU. Intel calls this Intel Resource Director Technology (Intel(R) RDT). More information about RDT can be found in the Intel x86 Architecture Software Developer Manual. AMD calls this AMD Platform Quality of Service (AMD QoS). More information about AMD QoS can be found in the AMD64 Technology Platform Quality of Service Extensions manual. Say N if unsure.
This option is needed for the systems that have more than 8 CPUs.
If you disable this option then the kernel will only support standard PC platforms. (which covers the vast majority of systems out there.) If you enable this option then you'll be able to select support for the following (non-PC) 32 bit x86 platforms: Goldfish (Android emulator) AMD Elan RDC R-321x SoC SGI 320/540 (Visual Workstation) STA2X11-based (e.g. Northville) Moorestown MID devices If you have one of these systems, or if you want to build a generic distribution kernel, say Y here - otherwise say N.
If you disable this option then the kernel will only support standard PC platforms. (which covers the vast majority of systems out there.) If you enable this option then you'll be able to select support for the following (non-PC) 64 bit x86 platforms: Numascale NumaChip ScaleMP vSMP SGI Ultraviolet If you have one of these systems, or if you want to build a generic distribution kernel, say Y here - otherwise say N.
Adds support for Numascale NumaChip large-SMP systems. Needed to enable more than ~168 cores. If you don't have one of these, you should say N here.
Support for ScaleMP vSMP systems. Say 'Y' here if this kernel is supposed to run on these EM64T-based machines. Only choose this option if you have one of these machines.
This option is needed in order to support SGI Ultraviolet systems. If you don't have one of these, you should say N here.
Enable support for the Goldfish virtual platform used primarily for Android development. Unless you are building for the Android Goldfish emulator say N here.
Select for the Intel CE media processor (CE4100) SOC. This option compiles in support for the CE4100 SOC for settop boxes and media devices.
Select to build a kernel capable of supporting Intel MID (Mobile Internet Device) platform systems which do not have the PCI legacy interfaces. If you are building for a PC class system say N here. Intel MID platforms are based on an Intel processor and chipset which consume less power than most of the x86 derivatives.
Select to include support for Quark X1000 SoC. Say Y here if you have a Quark based system such as the Arduino compatible Intel Galileo.
Select to build support for Intel Low Power Subsystem such as found on Intel Lynxpoint PCH. Selecting this option enables things like clock tree (common clock framework) and pincontrol which are needed by the LPSS peripheral drivers.
Select to interpret AMD specific ACPI device to platform device such as I2C, UART, GPIO found on AMD Carrizo and later chipsets. I2C and UART depend on COMMON_CLK to set clock. GPIO driver is implemented under PINCTRL subsystem.
This option enables sideband register access support for Intel SoC platforms. On these platforms the IOSF sideband is used in lieu of MSR's for some register accesses, mostly but not limited to thermal and power. Drivers may query the availability of this device to determine if they need the sideband in order to work on these platforms. The sideband is available on the following SoC products. This list is not meant to be exclusive. - BayTrail - Braswell - Quark You should say Y if you are running a kernel on one of these SoC's.
Select this option to expose the IOSF sideband access registers (MCR, MDR, MCRX) through debugfs to write and read register information from different units on the SoC. This is most useful for obtaining device state information for debug and analysis. As this is a general access mechanism, users of this option would have specific knowledge of the device they want to access. If you don't require the option or are in doubt, say N.
This option is needed for RDC R-321x system-on-chip, also known as R-8610-(G). If you don't have one of these chips, you should say N here.
This option compiles in the bigsmp and STA2X11 default subarchitectures. It is intended for a generic binary kernel. If you select them all, kernel will probe it one by one and will fallback to default.
This adds support for boards based on the STA2X11 IO-Hub, a.k.a. "ConneXt". The chip is used in place of the standard PC chipset, so all "standard" peripherals are missing. If this option is selected the kernel will still be able to boot on standard PC machines.
The Iris machines from EuroBraille do not have APM or ACPI support to shut themselves down properly. A special I/O sequence is needed to do so, which is what this module does at kernel shutdown. This is only for Iris machines from EuroBraille. If unused, say N.
Calculate simpler /proc/<PID>/wchan values. If this option is disabled then wchan values will recurse back to the caller function. This provides more accurate wchan values, at the expense of slightly more scheduling overhead. If in doubt, say "Y".
Say Y here to enable options for running Linux under various hyper- visors. This option enables basic hypervisor detection and platform setup. If you say N, all options in this submenu will be skipped and disabled, and Linux guest support won't be built in.
This changes the kernel so it can modify itself when it is run under a hypervisor, potentially improving performance significantly over full virtualization. However, when run without a hypervisor the kernel is theoretically slower and slightly larger.
Enable to debug paravirt_ops internals. Specifically, BUG if a paravirt_op is missing when it is called.
Paravirtualized spinlocks allow a pvops backend to replace the spinlock implementation with something virtualization-friendly (for example, block the virtual CPU rather than spinning). It has a minimal impact on native kernels and gives a nice performance benefit on paravirtualized KVM / Xen kernels. If you are unsure how to answer this question, answer Y.
This option enables various optimizations for running under the KVM hypervisor. It includes a paravirtualized clock, so that instead of relying on a PIT (or probably other) emulation by the underlying device model, the host provides the guest with timing infrastructure such as time of day, and system time
If virtualized under KVM, disable host haltpoll.
This option enables the PVH entry point for guest virtual machines as specified in the x86/HVM direct boot ABI.
Select this option to enable fine granularity task steal time accounting. Time spent executing other tasks in parallel with the current vCPU is discounted from the vCPU power. To account for that, there can be a small performance impact. If in doubt, say N here.
This option allows to run Linux as guest in a Jailhouse non-root cell. You can leave this option disabled if you only want to start Jailhouse and run Linux afterwards in the root cell.
This option allows to run Linux as guest in the ACRN hypervisor. ACRN is a flexible, lightweight reference open-source hypervisor, built with real-time and safety-criticality in mind. It is built for embedded IOT with small footprint and real-time features. More details can be found in https://projectacrn.org/.
Use the IA-PC HPET (High Precision Event Timer) to manage time in preference to the PIT and RTC, if a HPET is present. HPET is the next generation timer replacing legacy 8254s. The HPET provides a stable time base on SMP systems, unlike the TSC, but it is more expensive to access, as it is off-chip. The interface used is documented in the HPET spec, revision 1. You can safely choose Y here. However, HPET will only be activated if the platform and the BIOS support this feature. Otherwise the 8254 will be used for timing services. Choose N to continue using the legacy 8254 timer.
Enabled scanning of DMI to identify machine quirks. Say Y here unless you have verified that your setup is not affected by entries in the DMI blacklist. Required by PNP BIOS code.
Provides a driver for older AMD Athlon64/Opteron/Turion/Sempron GART based hardware IOMMUs. The GART supports full DMA access for devices with 32-bit access limitations, on systems with more than 3 GB. This is usually needed for USB, sound, many IDE/SATA chipsets and some other devices. Newer systems typically have a modern AMD IOMMU, supported via the CONFIG_AMD_IOMMU=y config option. In normal configurations this driver is only active when needed: there's more than 3 GB of memory and the system contains a 32-bit limited device. If unsure, say Y.
Enable maximum number of CPUS and NUMA Nodes for this architecture. If unsure, say N.
This allows you to specify the maximum number of CPUs which this kernel will support. If CPUMASK_OFFSTACK is enabled, the maximum supported value is 8192, otherwise the maximum value is 512. The minimum value which makes sense is 2. This is purely to save memory: each supported CPU adds about 8KB to the kernel image.
Multi-core scheduler support improves the CPU scheduler's decision making when dealing with multi-core CPU chips at a cost of slightly increased overhead in some places. If unsure say N here.
Intel Turbo Boost Max Technology 3.0 enabled CPUs have a core ordering determined at manufacturing time, which allows certain cores to reach higher turbo frequencies (when running single threaded workloads) than others. Enabling this kernel feature teaches the scheduler about the TBM3 (aka ITMT) priority order of the CPU cores and adjusts the scheduler's CPU selection logic accordingly, so that higher overall system performance can be achieved. This feature will have no effect on CPUs without this feature. If unsure say Y here.
A local APIC (Advanced Programmable Interrupt Controller) is an integrated interrupt controller in the CPU. If you have a single-CPU system which has a processor with a local APIC, you can say Y here to enable and use it. If you say Y here even though your machine doesn't have a local APIC, then the kernel will still run with no slowdown at all. The local APIC supports CPU-generated self-interrupts (timer, performance counters), and the NMI watchdog which detects hard lockups.
An IO-APIC (I/O Advanced Programmable Interrupt Controller) is an SMP-capable replacement for PC-style interrupt controllers. Most SMP systems and many recent uniprocessor systems have one. If you have a single-CPU system with an IO-APIC, you can say Y here to use it. If you say Y here even though your machine doesn't have an IO-APIC, then the kernel will still run with no slowdown at all.
This option enables a workaround that fixes a source of spurious interrupts. This is recommended when threaded interrupt handling is used on systems where the generation of superfluous "boot interrupts" cannot be disabled. Some chipsets generate a legacy INTx "boot IRQ" when the IRQ entry in the chipset's IO-APIC is masked (as, e.g. the RT kernel does during interrupt handling). On chipsets where this boot IRQ generation cannot be disabled, this workaround keeps the original IRQ line masked so that only the equivalent "boot IRQ" is delivered to the CPUs. The workaround also tells the kernel to set up the IRQ handler on the boot IRQ line. In this way only one interrupt is delivered to the kernel. Otherwise the spurious second interrupt may cause the kernel to bring down (vital) interrupt lines. Only affects "broken" chipsets. Interrupt sharing may be increased on these systems.
Machine Check support allows the processor to notify the kernel if it detects a problem (e.g. overheating, data corruption). The action the kernel takes depends on the severity of the problem, ranging from warning messages to halting the machine.
Enable support for /dev/mcelog which is needed by the old mcelog userspace logging daemon. Consider switching to the new generation rasdaemon solution.
Additional support for intel specific MCE features such as the thermal monitor.
Additional support for AMD specific MCE features such as the DRAM Error Threshold.
Include support for machine check handling on old Pentium 5 or WinChip systems. These typically need to be enabled explicitly on the command line.
Provide support for injecting machine checks for testing purposes. If you don't know what a machine check is and you don't do kernel QA it is safe to say n.
This option allows user programs to put the CPU into V8086 mode, which is an 80286-era approximation of 16-bit real mode. Some very old versions of X and/or vbetool require this option for user mode setting. Similarly, DOSEMU will use it if available to accelerate real mode DOS programs. However, any recent version of DOSEMU, X, or vbetool should be fully functional even without kernel VM86 support, as they will all fall back to software emulation. Nevertheless, if you are using a 16-bit DOS program where 16-bit performance matters, vm86 mode might be faster than emulation and you might want to enable this option. Note that any app that works on a 64-bit kernel is unlikely to need this option, as 64-bit kernels don't, and can't, support V8086 mode. This option is also unrelated to 16-bit protected mode and is not needed to run most 16-bit programs under Wine. Enabling this option increases the complexity of the kernel and slows down exception handling a tiny bit. If unsure, say N here.
This option is required by programs like Wine to run 16-bit protected mode legacy code on x86 processors. Disabling this option saves about 300 bytes on i386, or around 6K text plus 16K runtime memory on x86-64,
This enables emulation of the legacy vsyscall page. Disabling it is roughly equivalent to booting with vsyscall=none, except that it will also disable the helpful warning if a program tries to use a vsyscall. With this option set to N, offending programs will just segfault, citing addresses of the form 0xffffffffff600?00. This option is required by many programs built before 2013, and care should be used even with newer programs if set to N. Disabling this option saves about 7K of kernel size and possibly 4K of additional runtime pagetable memory.
This enables the ioperm() and iopl() syscalls which are necessary for legacy applications. Legacy IOPL support is an overbroad mechanism which allows user space aside of accessing all 65536 I/O ports also to disable interrupts. To gain this access the caller needs CAP_SYS_RAWIO capabilities and permission from potentially active security modules. The emulation restricts the functionality of the syscall to only allowing the full range I/O port access, but prevents the ability to disable interrupts from user space which would be granted if the hardware IOPL mechanism would be used.
This adds a driver to safely access the System Management Mode of the CPU on Toshiba portables with a genuine Toshiba BIOS. It does not work on models with a Phoenix BIOS. The System Management Mode is used to set the BIOS and power saving options on Toshiba portables. For information on utilities to make use of this driver see the Toshiba Linux utilities web site at: <http://www.buzzard.org.uk/toshiba/>. Say Y if you intend to run this kernel on a Toshiba portable. Say N otherwise.
This option enables legacy /proc/i8k userspace interface in hwmon dell-smm-hwmon driver. Character file /proc/i8k reports bios version, temperature and allows controlling fan speeds of Dell laptops via System Management Mode. For old Dell laptops (like Dell Inspiron 8000) it reports also power and hotkey status. For fan speed control is needed userspace package i8kutils. Say Y if you intend to run this kernel on old Dell laptops or want to use userspace package i8kutils. Say N otherwise.
This enables chipset and/or board specific fixups to be done in order to get reboot to work correctly. This is only needed on some combinations of hardware and BIOS. The symptom, for which this config is intended, is when reboot ends with a stalled/hung system. Currently, the only fixup is for the Geode machines using CS5530A and CS5536 chipsets and the RDC R-321x SoC. Say Y if you want to enable the fixup. Currently, it's safe to enable this option even if you don't need it. Say N otherwise.
If you say Y here, you will be able to update the microcode on Intel and AMD processors. The Intel support is for the IA32 family, e.g. Pentium Pro, Pentium II, Pentium III, Pentium 4, Xeon etc. The AMD support is for families 0x10 and later. You will obviously need the actual microcode binary data itself which is not shipped with the Linux kernel. The preferred method to load microcode from a detached initrd is described in Documentation/x86/microcode.rst. For that you need to enable CONFIG_BLK_DEV_INITRD in order for the loader to be able to scan the initrd for microcode blobs. In addition, you can build the microcode into the kernel. For that you need to add the vendor-supplied microcode to the CONFIG_EXTRA_FIRMWARE config option.
This options enables microcode patch loading support for Intel processors. For the current Intel microcode data package go to <https://downloadcenter.intel.com> and search for 'Linux Processor Microcode Data File'.
If you select this option, microcode patch loading support for AMD processors will be enabled.
DO NOT USE THIS! This is the ancient /dev/cpu/microcode interface which was used by userspace tools like iucode_tool and microcode.ctl. It is inadequate because it runs too late to be able to properly load microcode on a machine and it needs special tools. Instead, you should've switched to the early loading method with the initrd or builtin microcode by now: Documentation/x86/microcode.rst
This device gives privileged processes access to the x86 Model-Specific Registers (MSRs). It is a character device with major 202 and minors 0 to 31 for /dev/cpu/0/msr to /dev/cpu/31/msr. MSR accesses are directed to a specific CPU on multi-processor systems.
This device gives processes access to the x86 CPUID instruction to be executed on a specific processor. It is a character device with major 203 and minors 0 to 31 for /dev/cpu/0/cpuid to /dev/cpu/31/cpuid.
Linux can use up to 64 Gigabytes of physical memory on x86 systems. However, the address space of 32-bit x86 processors is only 4 Gigabytes large. That means that, if you have a large amount of physical memory, not all of it can be "permanently mapped" by the kernel. The physical memory that's not permanently mapped is called "high memory". If you are compiling a kernel which will never run on a machine with more than 1 Gigabyte total physical RAM, answer "off" here (default choice and suitable for most users). This will result in a "3GB/1GB" split: 3GB are mapped so that each process sees a 3GB virtual memory space and the remaining part of the 4GB virtual memory space is used by the kernel to permanently map as much physical memory as possible. If the machine has between 1 and 4 Gigabytes physical RAM, then answer "4GB" here. If more than 4 Gigabytes is used then answer "64GB" here. This selection turns Intel PAE (Physical Address Extension) mode on. PAE implements 3-level paging on IA32 processors. PAE is fully supported by Linux, PAE mode is implemented on all recent Intel processors (Pentium Pro and better). NOTE: If you say "64GB" here, then the kernel will not boot on CPUs that don't support PAE! The actual amount of total physical memory will either be auto detected or can be forced by using a kernel command line option such as "mem=256M". (Try "man bootparam" or see the documentation of your boot loader (lilo or loadlin) about how to pass options to the kernel at boot time.) If unsure, say "off".
Select this if you have a 32-bit processor and between 1 and 4 gigabytes of physical RAM.
Select this if you have a 32-bit processor and more than 4 gigabytes of physical RAM.
Select the desired split between kernel and user memory. If the address range available to the kernel is less than the physical memory installed, the remaining memory will be available as "high memory". Accessing high memory is a little more costly than low memory, as it needs to be mapped into the kernel first. Note that increasing the kernel address space limits the range available to user programs, making the address space there tighter. Selecting anything other than the default 3G/1G split will also likely make your kernel incompatible with binary-only kernel modules. If you are not absolutely sure what you are doing, leave this option alone! config VMSPLIT_3G bool "3G/1G user/kernel split" config VMSPLIT_3G_OPT depends on !X86_PAE bool "3G/1G user/kernel split (for full 1G low memory)" config VMSPLIT_2G bool "2G/2G user/kernel split" config VMSPLIT_2G_OPT depends on !X86_PAE bool "2G/2G user/kernel split (for full 2G low memory)" config VMSPLIT_1G bool "1G/3G user/kernel split"
PAE is required for NX support, and furthermore enables larger swapspace support for non-overcommit purposes. It has the cost of more pagetable lookup overhead, and also consumes more pagetable space per process.
5-level paging enables access to larger address space: upto 128 PiB of virtual address space and 4 PiB of physical address space. It will be supported by future Intel CPUs. A kernel with the option enabled can be booted on machines that support 4- or 5-level paging. See Documentation/x86/x86_64/5level-paging.rst for more information. Say N if unsure.
Certain kernel features effectively disable kernel linear 1 GB mappings (even if the CPU otherwise supports them), so don't confuse the user by printing that we have them enabled.
Expose statistics about the Change Page Attribute mechanism, which helps to determine the effectiveness of preserving large and huge page mappings when mapping protections are changed.
Say yes to enable support for the encryption of system memory. This requires an AMD processor that supports Secure Memory Encryption (SME).
Say yes to have system memory encrypted by default if running on an AMD processor that supports Secure Memory Encryption (SME). If set to Y, then the encryption of system memory can be deactivated with the mem_encrypt=off command line option. If set to N, then the encryption of system memory can be activated with the mem_encrypt=on command line option.
Enable NUMA (Non-Uniform Memory Access) support. The kernel will try to allocate memory used by a CPU on the local memory controller of the CPU and add some more NUMA awareness to the kernel. For 64-bit this is recommended if the system is Intel Core i7 (or later), AMD Opteron, or EM64T NUMA. For 32-bit this is only needed if you boot a 32-bit kernel on a 64-bit NUMA platform. Otherwise, you should say N.
Enable AMD NUMA node topology detection. You should say Y here if you have a multi processor AMD system. This uses an old method to read the NUMA configuration directly from the builtin Northbridge of Opteron. It is recommended to use X86_64_ACPI_NUMA instead, which also takes priority if both are compiled in.
Enable ACPI SRAT based node topology detection.
Enable NUMA emulation. A flat machine will be split into virtual nodes when booted with "numa=fake=N", where N is the number of nodes. This is only useful for debugging.
Specify the maximum number of NUMA Nodes available on the target system. Increases memory reserved to accommodate various tables.
This option enables a sysfs memory/probe interface for testing. See Documentation/admin-guide/mm/memory-hotplug.rst for more information. If you are unsure how to answer this question, answer N.
Treat memory marked using the non-standard e820 type of 12 as used by the Intel Sandy Bridge-EP reference BIOS as protected memory. The kernel will offer these regions to the 'pmem' driver so they can be used for persistent storage. Say Y if unsure.
The VM uses one page table entry for each page of physical memory. For systems with a lot of RAM, this can be wasteful of precious low memory. Setting this option will put user-space page table entries in high memory.
Periodically check for memory corruption in low memory, which is suspected to be caused by BIOS. Even when enabled in the configuration, it is disabled at runtime. Enable it by setting "memory_corruption_check=1" on the kernel command line. By default it scans the low 64k of memory every 60 seconds; see the memory_corruption_check_size and memory_corruption_check_period parameters in Documentation/admin-guide/kernel-parameters.rst to adjust this. When enabled with the default parameters, this option has almost no overhead, as it reserves a relatively small amount of memory and scans it infrequently. It both detects corruption and prevents it from affecting the running system. It is, however, intended as a diagnostic tool; if repeatable BIOS-originated corruption always affects the same memory, you can use memmap= to prevent the kernel from using that memory.
Set whether the default state of memory_corruption_check is on or off.
Specify the amount of low memory to reserve for the BIOS. The first page contains BIOS data structures that the kernel must not use, so that page must always be reserved. By default we reserve the first 64K of physical RAM, as a number of BIOSes are known to corrupt that memory range during events such as suspend/resume or monitor cable insertion, so it must not be used by the kernel. You can set this to 4 if you are absolutely sure that you trust the BIOS to get all its memory reservations and usages right. If you know your BIOS have problems beyond the default 64K area, you can set this to 640 to avoid using the entire low memory range. If you have doubts about the BIOS (e.g. suspend/resume does not work or there's kernel crashes after certain hardware hotplug events) then you might want to enable X86_CHECK_BIOS_CORRUPTION=y to allow the kernel to check typical corruption patterns. Leave this to the default value of 64 if you are unsure.
Linux can emulate a math coprocessor (used for floating point operations) if you don't have one. 486DX and Pentium processors have a math coprocessor built in, 486SX and 386 do not, unless you added a 487DX or 387, respectively. (The messages during boot time can give you some hints here ["man dmesg"].) Everyone needs either a coprocessor or this emulation. If you don't have a math coprocessor, you need to say Y here; if you say Y here even though you have a coprocessor, the coprocessor will be used nevertheless. (This behavior can be changed with the kernel command line option "no387", which comes handy if your coprocessor is broken. Try "man bootparam" or see the documentation of your boot loader (lilo or loadlin) about how to pass options to the kernel at boot time.) This means that it is a good idea to say Y here if you intend to use this kernel on different machines. More information about the internals of the Linux math coprocessor emulation can be found in <file:arch/x86/math-emu/README>. If you are not sure, say Y; apart from resulting in a 66 KB bigger kernel, it won't hurt.
On Intel P6 family processors (Pentium Pro, Pentium II and later) the Memory Type Range Registers (MTRRs) may be used to control processor access to memory ranges. This is most useful if you have a video (VGA) card on a PCI or AGP bus. Enabling write-combining allows bus write transfers to be combined into a larger transfer before bursting over the PCI/AGP bus. This can increase performance of image write operations 2.5 times or more. Saying Y here creates a /proc/mtrr file which may be used to manipulate your processor's MTRRs. Typically the X server should use this. This code has a reasonably generic interface so that similar control registers on other processors can be easily supported as well: The Cyrix 6x86, 6x86MX and M II processors have Address Range Registers (ARRs) which provide a similar functionality to MTRRs. For these, the ARRs are used to emulate the MTRRs. The AMD K6-2 (stepping 8 and above) and K6-3 processors have two MTRRs. The Centaur C6 (WinChip) has 8 MCRs, allowing write-combining. All of these processors are supported by this code and it makes sense to say Y here if you have one of them. Saying Y here also fixes a problem with buggy SMP BIOSes which only set the MTRRs for the boot CPU and not for the secondary CPUs. This can lead to all sorts of problems, so it's good to say Y here. You can safely say Y even if your machine doesn't have MTRRs, you'll just add about 9 KB to your kernel. See <file:Documentation/x86/mtrr.rst> for more information.
Convert MTRR layout from continuous to discrete, so X drivers can add writeback entries. Can be disabled with disable_mtrr_cleanup on the kernel command line. The largest mtrr entry size for a continuous block can be set with mtrr_chunk_size. If unsure, say Y.
Enable mtrr cleanup default value
mtrr cleanup spare entries default, it can be changed via mtrr_spare_reg_nr=N on the kernel command line.
Use PAT attributes to setup page level cache control. PATs are the modern equivalents of MTRRs and are much more flexible than MTRRs. Say N here if you see bootup problems (boot crash, boot hang, spontaneous reboots) or a non-working video driver. If unsure, say Y.
Enable the x86 architectural RDRAND instruction (Intel Bull Mountain technology) to generate random numbers. If supported, this is a high bandwidth, cryptographically secure hardware random number generator.
Supervisor Mode Access Prevention (SMAP) is a security feature in newer Intel processors. There is a small performance cost if this enabled and turned on; there is also a small increase in the kernel size if this is enabled. If unsure, say Y.
User Mode Instruction Prevention (UMIP) is a security feature in some x86 processors. If enabled, a general protection fault is issued if the SGDT, SLDT, SIDT, SMSW or STR instructions are executed in user mode. These instructions unnecessarily expose information about the hardware state. The vast majority of applications do not use these instructions. For the very few that do, software emulation is provided in specific cases in protected and virtual-8086 modes. Emulated results are dummy.
Memory Protection Keys provides a mechanism for enforcing page-based protections, but without requiring modification of the page tables when an application changes protection domains. For details, see Documentation/core-api/protection-keys.rst If unsure, say y.
Intel's TSX (Transactional Synchronization Extensions) feature allows to optimize locking protocols through lock elision which can lead to a noticeable performance boost. On the other hand it has been shown that TSX can be exploited to form side channel attacks (e.g. TAA) and chances are there will be more of those attacks discovered in the future. Therefore TSX is not enabled by default (aka tsx=off). An admin might override this decision by tsx=on the command line parameter. Even with TSX enabled, the kernel will attempt to enable the best possible TAA mitigation setting depending on the microcode available for the particular machine. This option allows to set the default tsx mode between tsx=on, =off and =auto. See Documentation/admin-guide/kernel-parameters.txt for more details. Say off if not sure, auto if TSX is in use but it should be used on safe platforms or on if TSX is in use and the security aspect of tsx is not relevant.
TSX is disabled if possible - equals to tsx=off command line parameter.
TSX is always enabled on TSX capable HW - equals the tsx=on command line parameter.
TSX is enabled on TSX capable HW that is believed to be safe against side channel attacks- equals the tsx=auto command line parameter.
Intel(R) Software Guard eXtensions (SGX) is a set of CPU instructions that can be used by applications to set aside private regions of code and data, referred to as enclaves. An enclave's private memory can only be accessed by code running within the enclave. Accesses from outside the enclave, including other enclaves, are disallowed by hardware. If unsure, say N.
This enables the kernel to use EFI runtime services that are available (such as the EFI variable services). This option is only useful on systems that have EFI firmware. In addition, you should use the latest ELILO loader available at <http://elilo.sourceforge.net> in order to take advantage of EFI runtime services. However, even with this option, the resultant kernel should continue to boot on existing non-EFI platforms.
This kernel feature allows a bzImage to be loaded directly by EFI firmware without the use of a bootloader. See Documentation/admin-guide/efi-stub.rst for more information.
Enabling this feature allows a 64-bit kernel to be booted on a 32-bit firmware, provided that your CPU supports 64-bit mode. Note that it is not possible to boot a mixed-mode enabled kernel via the EFI boot stub - a bootloader that supports the EFI handover protocol must be used. If unsure, say N.
kexec is a system call that implements the ability to shutdown your current kernel, and to start another kernel. It is like a reboot but it is independent of the system firmware. And like a reboot you can start any kernel with it, not just Linux. The name comes from the similarity to the exec system call. It is an ongoing process to be certain the hardware in a machine is properly shutdown, so do not be surprised if this code does not initially work for you. As of this writing the exact hardware interface is strongly in flux, so no good recommendation can be made.
This is new version of kexec system call. This system call is file based and takes file descriptors as system call argument for kernel and initramfs as opposed to list of segments as accepted by previous system call.
This option makes the kexec_file_load() syscall check for a valid signature of the kernel image. The image can still be loaded without a valid signature unless you also enable KEXEC_SIG_FORCE, though if there's a signature that we can check, then it must be valid. In addition to this option, you need to enable signature verification for the corresponding kernel image type being loaded in order for this to work.
This option makes kernel signature verification mandatory for the kexec_file_load() syscall.
Enable bzImage signature verification support.
Generate crash dump after being started by kexec. This should be normally only set in special crash dump kernels which are loaded in the main kernel with kexec-tools into a specially reserved region and then later executed after a crash by kdump/kexec. The crash dump kernel must be compiled to a memory address not used by the main kernel or BIOS using PHYSICAL_START, or it must be built as a relocatable image (CONFIG_RELOCATABLE=y). For more details see Documentation/admin-guide/kdump/kdump.rst
Jump between original kernel and kexeced kernel and invoke code in physical address mode via KEXEC
This gives the physical address where the kernel is loaded. If kernel is a not relocatable (CONFIG_RELOCATABLE=n) then bzImage will decompress itself to above physical address and run from there. Otherwise, bzImage will run from the address where it has been loaded by the boot loader and will ignore above physical address. In normal kdump cases one does not have to set/change this option as now bzImage can be compiled as a completely relocatable image (CONFIG_RELOCATABLE=y) and be used to load and run from a different address. This option is mainly useful for the folks who don't want to use a bzImage for capturing the crash dump and want to use a vmlinux instead. vmlinux is not relocatable hence a kernel needs to be specifically compiled to run from a specific memory area (normally a reserved region) and this option comes handy. So if you are using bzImage for capturing the crash dump, leave the value here unchanged to 0x1000000 and set CONFIG_RELOCATABLE=y. Otherwise if you plan to use vmlinux for capturing the crash dump change this value to start of the reserved region. In other words, it can be set based on the "X" value as specified in the "crashkernel=YM@XM" command line boot parameter passed to the panic-ed kernel. Please take a look at Documentation/admin-guide/kdump/kdump.rst for more details about crash dumps. Usage of bzImage for capturing the crash dump is recommended as one does not have to build two kernels. Same kernel can be used as production kernel and capture kernel. Above option should have gone away after relocatable bzImage support is introduced. But it is present because there are users out there who continue to use vmlinux for dump capture. This option should go away down the line. Don't change this unless you know what you are doing.
This builds a kernel image that retains relocation information so it can be loaded someplace besides the default 1MB. The relocations tend to make the kernel binary about 10% larger, but are discarded at runtime. One use is for the kexec on panic case where the recovery kernel must live at a different physical address than the primary kernel. Note: If CONFIG_RELOCATABLE=y, then the kernel runs from the address it has been loaded at and the compile time physical address (CONFIG_PHYSICAL_START) is used as the minimum location.
In support of Kernel Address Space Layout Randomization (KASLR), this randomizes the physical address at which the kernel image is decompressed and the virtual address where the kernel image is mapped, as a security feature that deters exploit attempts relying on knowledge of the location of kernel code internals. On 64-bit, the kernel physical and virtual addresses are randomized separately. The physical address will be anywhere between 16MB and the top of physical memory (up to 64TB). The virtual address will be randomized from 16MB up to 1GB (9 bits of entropy). Note that this also reduces the memory space available to kernel modules from 1.5GB to 1GB. On 32-bit, the kernel physical and virtual addresses are randomized together. They will be randomized from 16MB up to 512MB (8 bits of entropy). Entropy is generated using the RDRAND instruction if it is supported. If RDTSC is supported, its value is mixed into the entropy pool as well. If neither RDRAND nor RDTSC are supported, then entropy is read from the i8254 timer. The usable entropy is limited by the kernel being built using 2GB addressing, and that PHYSICAL_ALIGN must be at a minimum of 2MB. As a result, only 10 bits of entropy are theoretically possible, but the implementations are further limited due to memory layouts. If unsure, say Y.
This value puts the alignment restrictions on physical address where kernel is loaded and run from. Kernel is compiled for an address which meets above alignment restriction. If bootloader loads the kernel at a non-aligned address and CONFIG_RELOCATABLE is set, kernel will move itself to nearest address aligned to above value and run from there. If bootloader loads the kernel at a non-aligned address and CONFIG_RELOCATABLE is not set, kernel will ignore the run time load address and decompress itself to the address it has been compiled for and run from there. The address for which kernel is compiled already meets above alignment restrictions. Hence the end result is that kernel runs from a physical address meeting above alignment restrictions. On 32-bit this value must be a multiple of 0x2000. On 64-bit this value must be a multiple of 0x200000. Don't change this unless you know what you are doing.
This option makes base addresses of vmalloc and vmemmap as well as __PAGE_OFFSET movable during boot.
Randomizes the base virtual address of kernel memory sections (physical memory mapping, vmalloc & vmemmap). This security feature makes exploits relying on predictable memory locations less reliable. The order of allocations remains unchanged. Entropy is generated in the same way as RANDOMIZE_BASE. Current implementation in the optimal configuration have in average 30,000 different possible virtual addresses for each memory section. If unsure, say Y.
Define the padding in terabytes added to the existing physical memory size during kernel memory randomization. It is useful for memory hotplug support but reduces the entropy available for address randomization. If unsure, leave at the default value.
Set whether default state of cpu0_hotpluggable is on or off. Say Y here to enable CPU0 hotplug by default. If this switch is turned on, there is no need to give cpu0_hotplug kernel parameter and the CPU0 hotplug feature is enabled by default. Please note: there are two known CPU0 dependencies if you want to enable the CPU0 hotplug feature either by this switch or by cpu0_hotplug kernel parameter. First, resume from hibernate or suspend always starts from CPU0. So hibernate and suspend are prevented if CPU0 is offline. Second dependency is PIC interrupts always go to CPU0. CPU0 can not offline if any interrupt can not migrate out of CPU0. There may be other CPU0 dependencies. Please make sure the dependencies are under your control before you enable this feature. Say N if you don't want to enable CPU0 hotplug feature by default. You still can enable the CPU0 hotplug feature at boot by kernel parameter cpu0_hotplug.
Enabling this option offlines CPU0 (if CPU0 can be offlined) as soon as possible and boots up userspace with CPU0 offlined. User can online CPU0 back after boot time. To debug CPU0 hotplug, you need to enable CPU0 offline/online feature by either turning on CONFIG_BOOTPARAM_HOTPLUG_CPU0 during compilation or giving cpu0_hotplug kernel parameter at boot. If unsure, say N.
Certain buggy versions of glibc will crash if they are presented with a 32-bit vDSO that is not mapped at the address indicated in its segment table. The bug was introduced by f866314b89d56845f55e6f365e18b31ec978ec3a and fixed by 3b3ddb4f7db98ec9e912ccdf54d35df4aa30e04a and 49ad572a70b8aeb91e57483a11dd1b77e31c4468. Glibc 2.3.3 is the only released version with the bug, but OpenSUSE 9 contains a buggy "glibc 2.3.2". The symptom of the bug is that everything crashes on startup, saying: dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! Saying Y here changes the default value of the vdso32 boot option from 1 to 0, which turns off the 32-bit vDSO entirely. This works around the glibc bug but hurts performance. If unsure, say N: if you are compiling your own kernel, you are unlikely to be using a buggy version of glibc.
Legacy user code that does not know how to find the vDSO expects to be able to issue three syscalls by calling fixed addresses in kernel space. Since this location is not randomized with ASLR, it can be used to assist security vulnerability exploitation. This setting can be changed at boot time via the kernel command line parameter vsyscall=[emulate|xonly|none]. On a system with recent enough glibc (2.14 or newer) and no static binaries, you can say None without a performance penalty to improve security. If unsure, select "Emulate execution only". config LEGACY_VSYSCALL_EMULATE bool "Full emulation" help The kernel traps and emulates calls into the fixed vsyscall address mapping. This makes the mapping non-executable, but it still contains readable known contents, which could be used in certain rare security vulnerability exploits. This configuration is recommended when using legacy userspace that still uses vsyscalls along with legacy binary instrumentation tools that require code to be readable. An example of this type of legacy userspace is running Pin on an old binary that still uses vsyscalls. config LEGACY_VSYSCALL_XONLY bool "Emulate execution only" help The kernel traps and emulates calls into the fixed vsyscall address mapping and does not allow reads. This configuration is recommended when userspace might use the legacy vsyscall area but support for legacy binary instrumentation of legacy code is not needed. It mitigates certain uses of the vsyscall area as an ASLR-bypassing buffer. config LEGACY_VSYSCALL_NONE bool "None" help There will be no vsyscall mapping at all. This will eliminate any risk of ASLR bypass due to the vsyscall fixed address mapping. Attempts to use the vsyscalls will be reported to dmesg, so that either old or malicious userspace programs can be identified.
Allow for specifying boot arguments to the kernel at build time. On some systems (e.g. embedded ones), it is necessary or convenient to provide some or all of the kernel boot arguments with the kernel itself (that is, to not rely on the boot loader to provide them.) To compile command line arguments into the kernel, set this option to 'Y', then fill in the boot arguments in CONFIG_CMDLINE. Systems with fully functional boot loaders (i.e. non-embedded) should leave this option set to 'N'.
Enter arguments here that should be compiled into the kernel image and used at boot time. If the boot loader provides a command line at boot time, it is appended to this string to form the full kernel command line, when the system boots. However, you can use the CONFIG_CMDLINE_OVERRIDE option to change this behavior. In most cases, the command line (whether built-in or provided by the boot loader) should specify the device for the root file system.
Set this option to 'Y' to have the kernel ignore the boot loader command line, and use ONLY the built-in command line. This is used to work around broken boot loaders. This should be set to 'N' under normal conditions.
Linux can allow user programs to install a per-process x86 Local Descriptor Table (LDT) using the modify_ldt(2) system call. This is required to run 16-bit or segmented code such as DOSEMU or some Wine programs. It is also used by some very old threading libraries. Enabling this feature adds a small amount of overhead to context switches and increases the low-level kernel attack surface. Disabling it removes the modify_ldt(2) system call. Saying 'N' here may make sense for embedded or server kernels.
APM is a BIOS specification for saving power using several different
techniques. This is mostly useful for battery powered laptops with
APM compliant BIOSes. If you say Y here, the system time will be
reset after a RESUME operation, the /proc/apm device will provide
battery status information, and user-space programs will receive
notification of APM "events" (e.g. battery status change).
If you select "Y" here, you can disable actual use of the APM
BIOS by passing the "apm=off" option to the kernel at boot time.
Note that the APM support is almost completely disabled for
machines with more than one CPU.
In order to use APM, you will need supporting software. For location
and more information, read <file:Documentation/power/apm-acpi.rst>
and the Battery Powered Linux mini-HOWTO, available from
<http://www.tldp.org/docs.html#howto>.
This driver does not spin down disk drives (see the hdparm(8)
manpage ("man 8 hdparm") for that), and it doesn't turn off
VESA-compliant "green" monitors.
This driver does not support the TI 4000M TravelMate and the ACER
486/DX4/75 because they don't have compliant BIOSes. Many "green"
desktop machines also don't have compliant BIOSes, and this driver
may cause those machines to panic during the boot phase.
Generally, if you don't have a battery in your machine, there isn't
much point in using this driver and you should say N. If you get
random kernel OOPSes or reboots that don't seem to be related to
anything, try disabling/enabling this option (or disabling/enabling
APM in your BIOS).
Some other things you should try when experiencing seemingly random,
"weird" problems:
1) make sure that you have enough swap space and that it is
enabled.
2) pass the "no-hlt" option to the kernel
3) switch on floating point emulation in the kernel and pass
the "no387" option to the kernel
4) pass the "floppy=nodma" option to the kernel
5) pass the "mem=4M" option to the kernel (thereby disabling
all but the first 4 MB of RAM)
6) make sure that the CPU is not over clocked.
7) read the sig11 FAQ at <http://www.bitwizard.nl/sig11/>
8) disable the cache from your BIOS settings
9) install a fan for the video card or exchange video RAM
10) install a better fan for the CPU
11) exchange RAM chips
12) exchange the motherboard.
To compile this driver as a module, choose M here: the
module will be called apm.
This option will ignore USER SUSPEND requests. On machines with a compliant APM BIOS, you want to say N. However, on the NEC Versa M series notebooks, it is necessary to say Y because of a BIOS bug.
Enable APM features at boot time. From page 36 of the APM BIOS specification: "When disabled, the APM BIOS does not automatically power manage devices, enter the Standby State, enter the Suspend State, or take power saving steps in response to CPU Idle calls." This driver will make CPU Idle calls when Linux is idle (unless this feature is turned off -- see "Do CPU IDLE calls", below). This should always save battery power, but more complicated APM features will be dependent on your BIOS implementation. You may need to turn this option off if your computer hangs at boot time when using APM support, or if it beeps continuously instead of suspending. Turn this off if you have a NEC UltraLite Versa 33/C or a Toshiba T400CDT. This is off by default since most machines do fine without this feature.
Enable calls to APM CPU Idle/CPU Busy inside the kernel's idle loop. On some machines, this can activate improved power savings, such as a slowed CPU clock rate, when the machine is idle. These idle calls are made after the idle loop has run for some length of time (e.g., 333 mS). On some machines, this will cause a hang at boot time or whenever the CPU becomes idle. (On machines with more than one CPU, this option does nothing.)
Enable console blanking using the APM. Some laptops can use this to turn off the LCD backlight when the screen blanker of the Linux virtual console blanks the screen. Note that this is only used by the virtual console screen blanker, and won't turn off the backlight when using the X Window system. This also doesn't have anything to do with your VESA-compliant power-saving monitor. Further, this option doesn't work for all laptops -- it might not turn off your backlight at all, or it might print a lot of errors to the console, especially if you are using gpm.
Normally we disable external interrupts while we are making calls to the APM BIOS as a measure to lessen the effects of a badly behaving BIOS implementation. The BIOS should reenable interrupts if it needs to. Unfortunately, some BIOSes do not -- especially those in many of the newer IBM Thinkpads. If you experience hangs when you suspend, try setting this to Y. Otherwise, say N.
On PCI systems, the BIOS can be used to detect the PCI devices and determine their configuration. However, some old PCI motherboards have BIOS bugs and may crash if this is done. Also, some embedded PCI-based systems don't have any BIOS at all. Linux can also try to detect the PCI hardware directly without using the BIOS. With this option, you can specify how Linux should detect the PCI devices. If you choose "BIOS", the BIOS will be used, if you choose "Direct", the BIOS won't be used, and if you choose "MMConfig", then PCI Express MMCONFIG will be used. If you choose "Any", the kernel will try MMCONFIG, then the direct access method and falls back to the BIOS if that doesn't work. If unsure, go with the default, which is "Any".
Read the PCI windows out of the CNB20LE host bridge. This allows PCI hotplug to work on systems with the CNB20LE chipset which do not have ACPI. There's no public spec for this chipset, and this functionality is known to be incomplete. You should say N unless you know you need this.
Expose ISA bus device drivers and options available for selection and configuration. Enable this option if your target machine has an ISA bus. ISA is an older system, displaced by PCI and newer bus architectures -- if your target machine is modern, it probably does not have an ISA bus. If unsure, say N.
Enables ISA-style DMA support for devices requiring such controllers. If unsure, say Y.
Find out whether you have ISA slots on your motherboard. ISA is the name of a bus system, i.e. the way the CPU talks to the other stuff inside your box. Other bus systems are PCI, EISA, MicroChannel (MCA) or VESA. ISA is an older system, now being displaced by PCI; newer boards don't support it. If you have ISA, say Y, otherwise N.
This provides basic support for National Semiconductor's (now AMD's) Geode processors. The driver probes for the PCI-IDs of several on-chip devices, so its a good dependency for other scx200_* drivers. If compiled as a module, the driver is named scx200.
This driver provides a clocksource built upon the on-chip 27MHz high-resolution timer. Its also a workaround for NSC Geode SC-1100's buggy TSC, which loses time when the processor goes idle (as is done by the scheduler). The other workaround is idle=poll boot option.
Add support for detecting the unique features of the OLPC XO hardware.
Add support for poweroff and suspend of the OLPC XO-1 laptop.
Add support for the XO-1 real time clock, which can be used as a programmable wakeup source.
Add support for SCI-based features of the OLPC XO-1 laptop: - EC-driven system wakeups - Power button - Ebook switch - Lid switch - AC adapter status updates - Battery status updates
Add support for SCI-based features of the OLPC XO-1.5 laptop: - EC-driven system wakeups - AC adapter status updates - Battery status updates
This option enables system support for the PCEngines ALIX. At present this just sets up LEDs for GPIO control on ALIX2/3/6 boards. However, other system specific setup should get added here. Note: You must still enable the drivers for GPIO and LED support (GPIO_CS5535 & LEDS_GPIO) to actually use the LEDs Note: You have to set alix.force=1 for boards with Award BIOS.
This option enables system support for the Soekris Engineering net5501.
This option enables system support for the Traverse Technologies GEOS.
This option enables system support for the Technologic Systems TS-5500.
Firmwares often provide initial graphics framebuffers so the BIOS, bootloader or kernel can show basic video-output during boot for user-guidance and debugging. Historically, x86 used the VESA BIOS Extensions and EFI-framebuffers for this, which are mostly limited to x86. This option, if enabled, marks VGA/VBE/EFI framebuffers as generic framebuffers so the new generic system-framebuffer drivers can be used on x86. If the framebuffer is not compatible with the generic modes, it is advertised as fallback platform framebuffer so legacy drivers like efifb, vesafb and uvesafb can pick it up. If this option is not selected, all system framebuffers are always marked as fallback platform framebuffers as usual. Note: Legacy fbdev drivers, including vesafb, efifb, uvesafb, will not be able to pick up generic system framebuffers if this option is selected. You are highly encouraged to enable simplefb as replacement if you select this option. simplefb can correctly deal with generic system framebuffers. But you should still keep vesafb and others enabled as fallback if a system framebuffer is incompatible with simplefb. If unsure, say Y.
Include code to run legacy 32-bit programs under a 64-bit kernel. You should likely turn this on, unless you're 100% sure that you don't have any 32-bit programs left.
Support old a.out binaries in the 32bit emulation.
Include code to run binaries for the x32 native 32-bit ABI for 64-bit processors. An x32 process gets access to the full 64-bit register file and wide data path while leaving pointers at 32 bits for smaller memory footprint. You will need a recent binutils (2.22 or later) with elf32_x86_64 support enabled to compile a kernel with this option set.