1 Xen Hypervisor Command Line Options

This document covers the command line options which the Xen Hypervisor.

1.1 Types of parameter

Most parameters take the form option=value. Different options on the command line should be space delimited. All options are case sensitive, as are all values unless explicitly noted.

1.1.1 Boolean (<boolean>)

All boolean option may be explicitly enabled using a value of > yes, on, true, enable or 1

They may be explicitly disabled using a value of > no, off, false, disable or 0

In addition, a boolean option may be enabled by simply stating its name, and may be disabled by prefixing its name with no-.

1.1.1.1 Examples

Enable noreboot mode > noreboot=true

Disable x2apic support (if present) > x2apic=off

Enable synchronous console mode > sync_console

Explicitly specifying any value other than those listed above is undefined, as is stacking a no- prefix with an explicit value.

1.1.2 Integer (<integer>)

An integer parameter will default to decimal and may be prefixed with a - for negative numbers. Alternatively, a hexadecimal number may be used by prefixing the number with 0x, or an octal number may be used if a leading 0 is present.

Providing a string which does not validly convert to an integer is undefined.

1.1.3 Size (<size>)

A size parameter may be any integer, with a single size suffix

Without a size suffix, the default will be kilo. Providing a suffix other than those listed above is undefined.

1.1.4 String

Many parameters are more complicated and require more intricate configuration. The detailed description of each individual parameter specify which values are valid.

1.1.5 List

Some options take a comma separated list of values.

1.1.6 Combination

Some parameters act as combinations of the above, most commonly a mix of Boolean and String. These are noted in the relevant sections.

1.2 Parameter details

1.2.1 acpi

= force | ht | noirq | <boolean>

String, or Boolean to disable.

The acpi option is used to control a set of four related boolean flags; acpi_force, acpi_ht, acpi_noirq and acpi_disabled.

By default, Xen will scan the DMI data and blacklist certain systems which are known to have broken ACPI setups. Providing acpi=force will cause Xen to ignore the blacklist and attempt to use all ACPI features.

Using acpi=ht causes Xen to parse the ACPI tables enough to enumerate all CPUs, but will not use other ACPI features. This is not common, and only has an effect if your system is blacklisted.

The acpi=noirq option causes Xen to not parse the ACPI MADT table looking for IO-APIC entries. This is also not common, and any system which requires this option to function should be blacklisted. Additionally, this will not prevent Xen from finding IO-APIC entries from the MP tables.

Finally, any of the boolean false options can be used to disable ACPI usage entirely.

Because responsibility for ACPI processing is shared between Xen and the domain 0 kernel this option is automatically propagated to the domain 0 command line

1.2.2 acpi_apic_instance

= <integer>

Specify which ACPI MADT table to parse for APIC information, if more than one is present.

1.2.3 acpi_pstate_strict (x86)

= <boolean>

Default: false

Enforce checking that P-state transitions by the ACPI cpufreq driver actually result in the nominated frequency to be established. A warning message will be logged if that isn't the case.

1.2.4 acpi_skip_timer_override (x86)

= <boolean>

Instruct Xen to ignore timer-interrupt override.

1.2.5 acpi_sleep (x86)

= s3_bios | s3_mode

s3_bios instructs Xen to invoke video BIOS initialization during S3 resume.

s3_mode instructs Xen to set up the boot time (option vga=) video mode during S3 resume.

1.2.6 allow_unsafe (x86)

= <boolean>

Default: false

Force boot on potentially unsafe systems. By default Xen will refuse to boot on systems with the following errata:

1.2.7 altp2m (Intel)

= <boolean>

Default: false

Permit multiple copies of host p2m.

1.2.8 apic (x86)

= bigsmp | default

Override Xen's logic for choosing the APIC driver. By default, if there are more than 8 CPUs, Xen will switch to bigsmp over default.

1.2.9 apicv (Intel)

= <boolean>

Default: true

Permit Xen to use APIC Virtualisation Extensions. This is an optimisation available as part of VT-x, and allows hardware to take care of the guests APIC handling, rather than requiring emulation in Xen.

1.2.10 apic_verbosity (x86)

= verbose | debug

Increase the verbosity of the APIC code from the default value.

1.2.11 arat (x86)

= <boolean>

Default: true

Permit Xen to use "Always Running APIC Timer" support on compatible hardware in combination with cpuidle. This option is only expected to be useful for developers wishing Xen to fall back to older timing methods on newer hardware.

1.2.12 argo

= List of [ <bool>, mac-permissive=<bool> ]

Controls for the Argo hypervisor-mediated interdomain communication service.

The functionality that this option controls is only available when Xen has been compiled with the build setting for Argo enabled in the build configuration.

Argo is a interdomain communication mechanism, where Xen acts as the central point of authority. Guests may register memory rings to recieve messages, query the status of other domains, and send messages by hypercall, all subject to appropriate auditing by Xen. Argo is disabled by default.

1.2.13 asid (x86)

= <boolean>

Default: true

Permit Xen to use Address Space Identifiers. This is an optimisation which tags the TLB entries with an ID per vcpu. This allows for guest TLB flushes to be performed without the overhead of a complete TLB flush.

1.2.14 async-show-all (x86)

= <boolean>

Default: false

Forces all CPUs' full state to be logged upon certain fatal asynchronous exceptions (watchdog NMIs and unexpected MCEs).

1.2.15 ats (x86)

= <boolean>

Default: false

Permits Xen to set up and use PCI Address Translation Services. This is a performance optimisation for PCI Passthrough.

WARNING: Xen cannot currently safely use ATS because of its synchronous wait loops for Queued Invalidation completions.

1.2.16 availmem

= <size>

Default: 0 (no limit)

Specify a maximum amount of available memory, to which Xen will clamp the e820 table.

1.2.17 badpage

= List of [ <integer> | <integer>-<integer> ]

Specify that certain pages, or certain ranges of pages contain bad bytes and should not be used. For example, if your memory tester says that byte 0x12345678 is bad, you would place badpage=0x12345 on Xen's command line.

1.2.18 bootscrub

= idle | <boolean>

Default: idle

Scrub free RAM during boot. This is a safety feature to prevent accidentally leaking sensitive VM data into other VMs if Xen crashes and reboots.

In idle mode, RAM is scrubbed in background on all CPUs during idle-loop with a guarantee that memory allocations always provide scrubbed pages. This option reduces boot time on machines with a large amount of RAM while still providing security benefits.

1.2.19 bootscrub_chunk

= <size>

Default: 128M

Maximum RAM block size chunks to be scrubbed whilst holding the page heap lock and not running softirqs. Reduce this if softirqs are not being run frequently enough. Setting this to a high value may cause boot failure, particularly if the NMI watchdog is also enabled.

1.2.20 clocksource (x86)

= pit | hpet | acpi | tsc

If set, override Xen's default choice for the platform timer. Having TSC as platform timer requires being explicitly set. This is because TSC can only be safely used if CPU hotplug isn't performed on the system. On some platforms, the "maxcpus" option may need to be used to further adjust the number of allowed CPUs. When running on platforms that can guarantee a monotonic TSC across sockets you may want to adjust the "tsc" command line parameter to "stable:socket".

1.2.21 cmci-threshold (Intel)

= <integer>

Default: 2

Specify the event count threshold for raising Corrected Machine Check Interrupts. Specifying zero disables CMCI handling.

1.2.22 cmos-rtc-probe (x86)

= <boolean>

Default: false

Flag to indicate whether to probe for a CMOS Real Time Clock irrespective of ACPI indicating none to be there.

1.2.23 com1

1.2.24 com2

= <baud>[/<base-baud>][,[DPS][,[<io-base>|pci|amt][,[<irq>|msi][,[<port-bdf>][,[<bridge-bdf>]]]]]]

Both option com1 and com2 follow the same format.

A typical setup for most situations might be com1=115200,8n1

In addition to the above positional specification for UART parameters, name=value pair specfications are also supported. This is used to add flexibility for UART devices which require additional UART parameter configurations.

The comma separation still delineates positional parameters. Hence, unless the parameter is explicitly specified with name=value option, it will be considered a positional parameter.

The syntax consists of com1=(comma-separated positional parameters),(comma separated name-value pairs)

The accepted name keywords for name=value pairs are:

The following are examples of correct specifications:

com1=115200,8n1,0x3f8,4
com1=115200,8n1,0x3f8,4,reg_width=4,reg_shift=2
com1=baud=115200,parity=n,stop_bits=1,io_base=0x3f8,reg_width=4

1.2.25 conring_size

= <size>

Default: conring_size=16k

Specify the size of the console ring buffer.

1.2.26 console

= List of [ vga | com1[H,L] | com2[H,L] | pv | dbgp | none ]

Default: console=com1,vga

Specify which console(s) Xen should use.

vga indicates that Xen should try and use the vga graphics adapter.

com1 and com2 indicates that Xen should use serial ports 1 and 2 respectively. Optionally, these arguments may be followed by an H or L. H indicates that transmitted characters will have their MSB set, while received characters must have their MSB set. L indicates the converse; transmitted and received characters will have their MSB cleared. This allows a single port to be shared by two subsystems (e.g. console and debugger).

pv indicates that Xen should use Xen's PV console. This option is only available when used together with pv-in-pvh.

dbgp indicates that Xen should use a USB debug port.

none indicates that Xen should not use a console. This option only makes sense on its own.

1.2.27 console_timestamps

= none | date | datems | boot | raw

Default: none

Can be modified at runtime

Specify which timestamp format Xen should use for each console line.

For compatibility with the older boolean parameter, specifying console_timestamps alone will enable the date option.

1.2.28 console_to_ring

= <boolean>

Default: false

Flag to indicate whether all guest console output should be copied into the console ring buffer.

1.2.29 conswitch

= <switch char>[x]

Default: conswitch=a

Can be modified at runtime

Specify which character should be used to switch serial input between Xen and dom0. The required sequence is CTRL-<switch char> three times.

The optional trailing x indicates that Xen should not automatically switch the console input to dom0 during boot. Any other value, including omission, causes Xen to automatically switch to the dom0 console during dom0 boot. Use conswitch=ax to keep the default switch character, but for xen to keep the console.

1.2.30 core_parking

= power | performance

Default: power

1.2.31 cpu_type (x86)

= arch_perfmon

If set, force use of the performance counters for oprofile, rather than detecting available support.

1.2.32 cpufreq

= none | {{ <boolean> | xen } [:[powersave|performance|ondemand|userspace][,<maxfreq>][,[<minfreq>][,[verbose]]]]} | dom0-kernel

Default: xen

Indicate where the responsibility for driving power states lies. Note that the choice of dom0-kernel is deprecated and not supported by all Dom0 kernels.

1.2.33 cpuid (x86)

= List of comma separated booleans

This option allows for fine tuning of the facilities Xen will use, after accounting for hardware capabilities as enumerated via CPUID.

Currently accepted:

The Speculation Control hardware features md-clear, ibrsb, stibp, ibpb, l1d-flush and ssbd are used by default if available and applicable. They can be ignored, e.g. no-ibrsb, at which point Xen won't use them itself, and won't offer them to guests.

1.2.34 cpuid_mask_cpu

= fam_0f_rev_[cdefg] | fam_10_rev_[bc] | fam_11_rev_b

Applicability: AMD

If none of the other cpuid_mask_* options are given, Xen has a set of pre-configured masks to make the current processor appear to be family/revision specified.

See below for general information on masking.

Warning: This option is not fully effective on Family 15h processors or later.

1.2.35 cpuid_mask_ecx

1.2.36 cpuid_mask_edx

1.2.37 cpuid_mask_ext_ecx

1.2.38 cpuid_mask_ext_edx

1.2.39 cpuid_mask_l7s0_eax

1.2.40 cpuid_mask_l7s0_ebx

1.2.41 cpuid_mask_thermal_ecx

1.2.42 cpuid_mask_xsave_eax

= <integer>

Applicability: x86. Default: ~0 (all bits set)

The availability of these options are model specific. Some processors don't support any of them, and no processor supports all of them. Xen will ignore options on processors which are lacking support.

These options can be used to alter the features visible via the CPUID instruction. Settings applied here take effect globally, including for Xen and all guests.

Note: Since Xen 4.7, it is no longer necessary to mask a host to create migration safety in heterogeneous scenarios. All necessary CPUID settings should be provided in the VM configuration file. Furthermore, it is recommended not to use this option, as doing so causes an unnecessary reduction of features at Xen's disposal to manage guests.

1.2.43 cpuidle (x86)

= <boolean>

1.2.44 cpuinfo (x86)

= <boolean>

1.2.45 crashinfo_maxaddr

= <size>

Default: 4G

Specify the maximum address to allocate certain structures, if used in combination with the low_crashinfo command line option.

1.2.46 crashkernel

= <ramsize-range>:<size>[,...][{@,<}<offset>] = <size>[{@,<}<offset>] = <size>,below=offset

Specify sizes and optionally placement of the crash kernel reservation area. The <ramsize-range>:<size> pairs indicate how much memory to set aside for a crash kernel (<size>) for a given range of installed RAM (<ramsize-range>). Each <ramsize-range> is of the form <start>-[<end>].

A trailing @<offset> specifies the exact address this area should be placed at, whereas < in place of @ just specifies an upper bound of the address range the area should fall into.

< and below are synonyomous, the latter being useful for grub2 systems which would otherwise require escaping of the < option

1.2.47 credit2_balance_over

= <integer>

1.2.48 credit2_balance_under

= <integer>

1.2.49 credit2_cap_period_ms

= <integer>

Default: 10

Domains subject to a cap receive a replenishment of their runtime budget once every cap period interval. Default is 10 ms. The amount of budget they receive depends on their cap. For instance, a domain with a 50% cap will receive 50% of 10 ms, so 5 ms.

1.2.50 credit2_load_precision_shift

= <integer>

Default: 18

Specify the number of bits to use for the fractional part of the values involved in Credit2 load tracking and load balancing math.

1.2.51 credit2_load_window_shift

= <integer>

Default: 30

Specify the number of bits to use to represent the length of the window (in nanoseconds) we use for load tracking inside Credit2. This means that, with the default value (30), we use 2^30 nsec ~= 1 sec long window.

Load tracking is done by means of a variation of exponentially weighted moving average (EWMA). The window length defined here is what tells for how long we give value to previous history of the load itself. In fact, after a full window has passed, what happens is that we discard all previous history entirely.

A short window will make the load balancer quick at reacting to load changes, but also short-sighted about previous history (and hence, e.g., long term load trends). A long window will make the load balancer thoughtful of previous history (and hence capable of capturing, e.g., long term load trends), but also slow in responding to load changes.

The default value of 1 sec is rather long.

1.2.52 credit2_runqueue

= cpu | core | socket | node | all

Default: socket

Specify how host CPUs are arranged in runqueues. Runqueues are kept balanced with respect to the load generated by the vCPUs running on them. Smaller runqueues (as in with core) means more accurate load balancing (for instance, it will deal better with hyperthreading), but also more overhead.

Available alternatives, with their meaning, are: * cpu: one runqueue per each logical pCPUs of the host; * core: one runqueue per each physical core of the host; * socket: one runqueue per each physical socket (which often, but not always, matches a NUMA node) of the host; * node: one runqueue per each NUMA node of the host; * all: just one runqueue shared by all the logical pCPUs of the host

1.2.53 dbgp

= ehci[ <integer> | @pci<bus>:<slot>.<func> ]

Specify the USB controller to use, either by instance number (when going over the PCI busses sequentially) or by PCI device (must be on segment 0).

1.2.54 debug_stack_lines

= <integer>

Default: 20

Limits the number lines printed in Xen stack traces.

1.2.55 debugtrace

= <integer>

Default: 128

Specify the size of the console debug trace buffer in KiB. The debug trace feature is only enabled in debugging builds of Xen.

1.2.56 dma_bits

= <integer>

Specify the bit width of the DMA heap.

1.2.57 dom0

= List of [ pv | pvh, shadow=<bool>, verbose=<bool> ]

Applicability: x86

Controls for how dom0 is constructed on x86 systems.

1.2.58 dom0-iommu

= List of [ passthrough=<bool>, strict=<bool>, map-inclusive=<bool>,
            map-reserved=<bool>, none ]

Controls for the dom0 IOMMU setup.

1.2.59 dom0_ioports_disable (x86)

= List of <hex>-<hex>

Specify a list of IO ports to be excluded from dom0 access.

1.2.60 dom0_max_vcpus

Either:

= <integer>.

The number of VCPUs to give to dom0. This number of VCPUs can be more than the number of PCPUs on the host. The default is the number of PCPUs.

Or:

= <min>-<max> where <min> and <max> are integers.

Gives dom0 a number of VCPUs equal to the number of PCPUs, but always at least <min> and no more than <max>. Using <min> may give more VCPUs than PCPUs. <min> or <max> may be omitted and the defaults of 1 and unlimited respectively are used instead.

For example, with dom0_max_vcpus=4-8:

   Number of
PCPUs | Dom0 VCPUs
 2    |  4
 4    |  4
 6    |  6
 8    |  8
10    |  8

1.2.61 dom0_mem (ARM)

= <size>

Set the amount of memory for the initial domain (dom0). It must be greater than zero. This parameter is required.

1.2.62 dom0_mem (x86)

= List of ( min:<sz> | max:<sz> | <sz> )

Set the amount of memory for the initial domain (dom0). If a size is positive, it represents an absolute value. If a size is negative, it is subtracted from the total available memory.

If <sz> is not specified, the default is all the available memory minus some reserve. The reserve is 1/16 of the available memory or 128 MB (whichever is smaller).

The amount of memory will be at least the minimum but never more than the maximum (i.e., max overrides the min option). If there isn't enough memory then as much as possible is allocated.

max:<sz> also sets the maximum reservation (the maximum amount of memory dom0 can balloon up to). If this is omitted then the maximum reservation is unlimited.

For example, to set dom0's initial memory allocation to 512MB but allow it to balloon up as far as 1GB use dom0_mem=512M,max:1G

<sz> is: <size> | [<size>+]<frac>% <frac> is an integer < 100

So <sz> being 1G+25% on a 256 GB host would result in 65 GB.

If you use this option then it is highly recommended that you disable any dom0 autoballooning feature present in your toolstack. See the xl.conf(5) man page or Xen Best Practices.

This option doesn't have effect if pv-shim mode is enabled.

1.2.63 dom0_nodes (x86)

= List of [ <integer> | relaxed | strict ]

Default: strict

Specify the NUMA nodes to place Dom0 on. Defaults for vCPU-s created and memory assigned to Dom0 will be adjusted to match the node restrictions set up here. Note that the values to be specified here are ACPI PXM ones, not Xen internal node numbers. relaxed sets up vCPU affinities to prefer but be not limited to the specified node(s).

1.2.64 dom0_vcpus_pin

= <boolean>

Default: false

Pin dom0 vcpus to their respective pcpus

1.2.65 dtuart (ARM)

= path [:options]

Default: ""

Specify the full path in the device tree for the UART. If the path doesn't start with /, it is assumed to be an alias. The options are device specific.

1.2.66 e820-mtrr-clip (x86)

= <boolean>

Flag that specifies if RAM should be clipped to the highest cacheable MTRR.

Default: true on Intel CPUs, otherwise false

1.2.67 e820-verbose (x86)

= <boolean>

Default: false

Flag that enables verbose output when processing e820 information and applying clipping.

1.2.68 edd (x86)

= off | on | skipmbr

Control retrieval of Extended Disc Data (EDD) from the BIOS during boot.

1.2.69 edid (x86)

= no | force

Either force retrieval of monitor EDID information via VESA DDC, or disable it (edid=no). This option should not normally be required except for debugging purposes.

1.2.70 efi

= List of [ rs=<bool>, attr=no|uc ]

Controls for interacting with the system Extended Firmware Interface.

1.2.71 ept

= List of [ ad=<bool>, pml=<bool> ]

Applicability: Intel

Extended Page Tables are a feature of Intel's VT-x technology, whereby hardware manages the virtualisation of HVM guest pagetables. EPT was introduced with the Nehalem architecture.

1.2.72 extra_guest_irqs

= [<domU number>][,<dom0 number>]

Default: 32,<variable>

Change the number of PIRQs available for guests. The optional first number is common for all domUs, while the optional second number (preceded by a comma) is for dom0. Changing the setting for domU has no impact on dom0 and vice versa. For example to change dom0 without changing domU, use extra_guest_irqs=,512. The default value for Dom0 and an eventual separate hardware domain is architecture dependent. Note that specifying zero as domU value means zero, while for dom0 it means to use the default.

1.2.73 flask

= permissive | enforcing | late | disabled

Default: enforcing

Specify how the FLASK security server should be configured. This option is only available if the hypervisor was compiled with FLASK support. This can be enabled by running either: - make -C xen config and enabling XSM and FLASK. - make -C xen menuconfig and enabling 'FLux Advanced Security Kernel support' and 'Xen Security Modules support'

1.2.74 font

= <height> where height is 8x8 | 8x14 | 8x16

Specify the font size when using the VESA console driver.

1.2.75 force-ept (Intel)

= <boolean>

Default: false

Allow EPT to be enabled when VMX feature VM_ENTRY_LOAD_GUEST_PAT is not present.

Warning: Due to CVE-2013-2212, VMX feature VM_ENTRY_LOAD_GUEST_PAT is by default required as a prerequisite for using EPT. If you are not using PCI Passthrough, or trust the guest administrator who would be using passthrough, then the requirement can be relaxed. This option is particularly useful for nested virtualization, to allow the L1 hypervisor to use EPT even if the L0 hypervisor does not provide VM_ENTRY_LOAD_GUEST_PAT.

1.2.76 gdb

= com1[H,L] | com2[H,L] | dbgp

Default: ``

Specify which console gdbstub should use. See console.

1.2.77 gnttab

= List of [ max-ver:<integer>, transitive=<bool> ]

Default: gnttab=max-ver:2,transitive

Control various aspects of the grant table behaviour available to guests.

The usage of gnttab v2 is not security supported on ARM platforms.

1.2.78 gnttab_max_frames

= <integer>

Default: 64

Can be modified at runtime

Specify the maximum number of frames which any domain may use as part of its grant table. This value is an upper boundary of the per-domain value settable via Xen tools.

Dom0 is using this value for sizing its grant table.

1.2.79 gnttab_max_maptrack_frames

= <integer>

Default: 1024

Can be modified at runtime

Specify the maximum number of frames to use as part of a domains maptrack array. This value is an upper boundary of the per-domain value settable via Xen tools.

Dom0 is using this value for sizing its maptrack table.

1.2.80 guest_loglvl

= <level>[/<rate-limited level>] where level is none | error | warning | info | debug | all

Default: guest_loglvl=none/warning

Can be modified at runtime

Set the logging level for Xen guests. Any log message with equal more more importance will be printed.

The optional <rate-limited level> option instructs which severities should be rate limited.

1.2.81 hap (x86)

= <boolean>

Default: true

Flag to globally enable or disable support for Hardware Assisted Paging (HAP)

1.2.82 hap_1gb (x86)

= <boolean>

Default: true

Flag to enable 1 GB host page table support for Hardware Assisted Paging (HAP).

1.2.83 hap_2mb (x86)

= <boolean>

Default: true

Flag to enable 2 MB host page table support for Hardware Assisted Paging (HAP).

1.2.84 hardware_dom

= <domid>

Default: 0

Enable late hardware domain creation using the specified domain ID. This is intended to be used when domain 0 is a stub domain which builds a disaggregated system including a hardware domain with the specified domain ID. This option is supported only when compiled with XSM on x86.

1.2.85 hest_disable

= <boolean>

Default: false

Control Xens use of the APEI Hardware Error Source Table, should one be found.

1.2.86 highmem-start (x86)

= <size>

Specify the memory boundary past which memory will be treated as highmem (x86 debug hypervisor only).

1.2.87 hmp-unsafe (arm)

= <boolean>

Default : false

Say yes at your own risk if you want to enable heterogenous computing (such as big.LITTLE). This may result to an unstable and insecure platform, unless you manually specify the cpu affinity of all domains so that all vcpus are scheduled on the same class of pcpus (big or LITTLE but not both). vcpu migration between big cores and LITTLE cores is not supported. See docs/misc/arm/big.LITTLE.txt for more information.

When the hmp-unsafe option is disabled (default), CPUs that are not identical to the boot CPU will be parked and not used by Xen.

1.2.88 hpetbroadcast (x86)

= <boolean>

1.2.89 hvm_debug (x86)

= <integer>

The specified value is a bit mask with the individual bits having the following meaning:

Bit  0 - debug level 0 (unused at present)
Bit  1 - debug level 1 (Control Register logging)
Bit  2 - debug level 2 (VMX logging of MSR restores when context switching)
Bit  3 - debug level 3 (unused at present)
Bit  4 - I/O operation logging
Bit  5 - vMMU logging
Bit  6 - vLAPIC general logging
Bit  7 - vLAPIC timer logging
Bit  8 - vLAPIC interrupt logging
Bit  9 - vIOAPIC logging
Bit 10 - hypercall logging
Bit 11 - MSR operation logging

Recognized in debug builds of the hypervisor only.

1.2.90 hvm_fep (x86)

= <boolean>

Default: false

Allow use of the Forced Emulation Prefix in HVM guests, to allow emulation of arbitrary instructions.

This option is intended for development and testing purposes.

Warning As this feature opens up the instruction emulator to arbitrary instruction from an HVM guest, don't use this in production system. No security support is provided when this flag is set.

1.2.91 hvm_port80 (x86)

= <boolean>

Default: true

Specify whether guests are to be given access to physical port 80 (often used for debugging purposes), to override the DMI based detection of systems known to misbehave upon accesses to that port.

1.2.92 idle_latency_factor (x86)

= <integer>

1.2.93 ioapic_ack (x86)

= old | new

Default: new unless directed-EOI is supported

1.2.94 iommu

= List of [ <bool>, verbose, debug, force, required,
            sharept, intremap, intpost, crash-disable,
            snoop, qinval, igfx, amd-iommu-perdev-intremap,
            dom0-{passthrough,strict} ]

All sub-options are boolean in nature.

I/O Memory Memory Units perform a function similar to the CPU MMU (hence the name), but typically exist as a discrete device, integrated as part of a PCI Root Complex. The most common configuration is to have one IOMMU per package (for on-die PCIe devices and directly attached PCIe lanes), and one IOMMU covering the remaining I/O in the system.

The functionality in an IOMMU commonly falls into two orthogonal categories:

  1. DMA remapping which uses a pagetable-like hierarchical structure and maps I/O Virtual Addresses (DFNs - Device Frame Numbers in Xen's terminology) to System Physical Addresses (MFNs - Machine Frame Numbers in Xen's terminology).

  2. Interrupt Remapping, which controls incoming Message Signalled Interrupt requests, including their routing to specific CPUs.

IOMMU functionality can be used to provide a translation which the hardware device driver isn't aware of (e.g. PCI Passthrough and a native driver inside the guest) and/or to enforce fine-grained control over the memory and interrupts which a device is attempting to access.

By default, IOMMUs are configured for use if they are available. An overall boolean (e.g. iommu=no) can override this and leave the IOMMUs disabled.

The following options are specific to Intel VT-d hardware:

The following options are specific to AMD-Vi hardware:

WARNING: The dom0-passthrough and dom0-strict booleans are both deprecated, and superseded by dom0-iommu={passthrough,strict} respectively - using both the old and new command line options in combination is undefined.

1.2.95 iommu_dev_iotlb_timeout

= <integer>

Default: 1000

Specify the timeout of the device IOTLB invalidation in milliseconds. By default, the timeout is 1000 ms. When you see error 'Queue invalidate wait descriptor timed out', try increasing this value.

1.2.96 iommu_inclusive_mapping

= <boolean>

WARNING: This command line option is deprecated, and superseded by dom0-iommu=map-inclusive - using both options in combination is undefined.

1.2.97 irq_ratelimit (x86)

= <integer>

1.2.98 irq_vector_map (x86)

1.2.99 ivrs_hpet[<hpet>] (AMD)

=[<seg>:]<bus>:<device>.<func>

Force the use of [<seg>:]<bus>:<device>.<func> as device ID of HPET <hpet> instead of the one specified by the IVHD sub-tables of the IVRS ACPI table.

1.2.100 ivrs_ioapic[<ioapic>] (AMD)

=[<seg>:]<bus>:<device>.<func>

Force the use of [<seg>:]<bus>:<device>.<func> as device ID of IO-APIC <ioapic> instead of the one specified by the IVHD sub-tables of the IVRS ACPI table.

1.2.101 lapic (x86)

= <boolean>

Force the use of use of the local APIC on a uniprocessor system, even if left disabled by the BIOS.

1.2.102 lapic_timer_c2_ok (x86)

= <boolean>

1.2.103 ler (x86)

= <boolean>

Default: false

This option is intended for debugging purposes only. Enable MSR_DEBUGCTL.LBR in hypervisor context to be able to dump the Last Interrupt/Exception To/From record with other registers.

1.2.104 loglvl

= <level>[/<rate-limited level>] where level is none | error | warning | info | debug | all

Default: loglvl=warning

Can be modified at runtime

Set the logging level for Xen. Any log message with equal more more importance will be printed.

The optional <rate-limited level> option instructs which severities should be rate limited.

1.2.105 low_crashinfo

= none | min | all

Default: none if not specified at all, or to min if low_crashinfo is present without qualification.

This option is only useful for hosts with a 32bit dom0 kernel, wishing to use kexec functionality in the case of a crash. It represents which data structures should be deliberately allocated in low memory, so the crash kernel may find find them. Should be used in combination with crashinfo_maxaddr.

1.2.106 low_mem_virq_limit

= <size>

Default: 64M

Specify the threshold below which Xen will inform dom0 that the quantity of free memory is getting low. Specifying 0 will disable this notification.

1.2.107 maxcpus (x86)

= <integer>

Specify the maximum number of CPUs that should be brought up.

This option is ignored in pv-shim mode.

1.2.108 max_cstate (x86)

= <integer>

1.2.109 max_gsi_irqs (x86)

= <integer>

Specifies the number of interrupts to be use for pin (IO-APIC or legacy PIC) based interrupts. Any higher IRQs will be available for use via PCI MSI.

1.2.110 max_lpi_bits (arm)

= <integer>

Specifies the number of ARM GICv3 LPI interrupts to allocate on the host, presented as the number of bits needed to encode it. This must be at least 14 and not exceed 32, and each LPI requires one byte (configuration) and one pending bit to be allocated. Defaults to 20 bits (to cover at most 1048576 interrupts).

1.2.111 mce (x86)

= <integer>

1.2.112 mce_fb (Intel)

= <integer>

1.2.113 mce_verbosity (x86)

= verbose

Specify verbose machine check output.

1.2.114 mem (x86)

= <size>

Specify the maximum address of physical RAM. Any RAM beyond this limit is ignored by Xen.

1.2.115 memop-max-order

= [<domU>][,[<ctldom>][,[<hwdom>][,<ptdom>]]]

x86 default: 9,18,12,12 ARM default: 9,18,10,10

Change the maximum order permitted for allocation (or allocation-like) requests issued by the various kinds of domains (in this order: ordinary DomU, control domain, hardware domain, and - when supported by the platform - DomU with pass-through device assigned).

1.2.116 mmcfg (x86)

= <boolean>[,amd-fam10]

Default: 1

Specify if the MMConfig space should be enabled.

1.2.117 mmio-relax (x86)

= <boolean> | all

Default: false

By default, domains may not create cached mappings to MMIO regions. This option relaxes the check for Domain 0 (or when using all, all PV domains), to permit the use of cacheable MMIO mappings.

1.2.118 msi (x86)

= <boolean>

Default: true

Force Xen to (not) use PCI-MSI, even if ACPI FADT says otherwise.

1.2.119 mtrr.show (x86)

= <boolean>

Default: false

Print boot time MTRR state.

1.2.120 mwait-idle (x86)

= <boolean>

Default: true

Use the MWAIT idle driver (with model specific C-state knowledge) instead of the ACPI based one.

1.2.121 nmi (x86)

= ignore | dom0 | fatal

Default: fatal for a debug build, or dom0 for a non-debug build

Specify what Xen should do in the event of an NMI parity or I/O error. ignore discards the error; dom0 causes Xen to report the error to dom0, while 'fatal' causes Xen to print diagnostics and then hang.

1.2.122 noapic (x86)

Instruct Xen to ignore any IOAPICs that are present in the system, and instead continue to use the legacy PIC. This is not recommended with pvops type kernels.

Because responsibility for APIC setup is shared between Xen and the domain 0 kernel this option is automatically propagated to the domain 0 command line.

1.2.123 invpcid (x86)

= <boolean>

Default: true

By default, Xen will use the INVPCID instruction for TLB management if it is available. This option can be used to cause Xen to fall back to older mechanisms, which are generally slower.

1.2.124 noirqbalance (x86)

= <boolean>

Disable software IRQ balancing and affinity. This can be used on systems such as Dell 1850/2850 that have workarounds in hardware for IRQ routing issues.

1.2.125 nolapic (x86)

= <boolean>

Default: false

Ignore the local APIC on a uniprocessor system, even if enabled by the BIOS.

1.2.126 no-real-mode (x86)

= <boolean>

Do not execute real-mode bootstrap code when booting Xen. This option should not be used except for debugging. It will effectively disable the vga option, which relies on real mode to set the video mode.

1.2.127 noreboot

= <boolean>

Do not automatically reboot after an error. This is useful for catching debug output. Defaults to automatically reboot after 5 seconds.

1.2.128 nosmp (x86)

= <boolean>

Disable SMP support. No secondary processors will be booted. Defaults to booting secondary processors.

This option is ignored in pv-shim mode.

1.2.129 nr_irqs (x86)

= <integer>

1.2.130 numa (x86)

= on | off | fake=<integer> | noacpi

Default: on

1.2.131 pci

= List of [ serr=<bool>, perr=<bool> ]

Default: Signaling left as set by firmware.

Override the firmware settings, and explicitly enable or disable the signalling of PCI System and Parity errors.

1.2.132 pci-phantom

=[<seg>:]<bus>:<device>,<stride>

Mark a group of PCI devices as using phantom functions without actually advertising so, so the IOMMU can create translation contexts for them.

All numbers specified must be hexadecimal ones.

This option can be specified more than once (up to 8 times at present).

1.2.133 pcid (x86)

= <boolean> | xpti=<bool>

Default: xpti

Can be modified at runtime (change takes effect only for domains created afterwards)

If available, control usage of the PCID feature of the processor for 64-bit pv-domains. PCID can be used either for no domain at all (false), for all of them (true), only for those subject to XPTI (xpti) or for those not subject to XPTI (no-xpti). The feature is used only in case INVPCID is supported and not disabled via invpcid=false.

1.2.134 pku (x86)

= <boolean>

Default: true

Flag to enable Memory Protection Keys.

The protection-key feature provides an additional mechanism by which IA-32e paging controls access to usermode addresses.

1.2.135 ple_gap

= <integer>

1.2.136 ple_window (Intel)

= <integer>

1.2.137 psr (Intel)

= List of ( cmt:<boolean> | rmid_max:<integer> | cat:<boolean> | cos_max:<integer> | cdp:<boolean> )

Default: psr=cmt:0,rmid_max:255,cat:0,cos_max:255,cdp:0

Platform Shared Resource(PSR) Services. Intel Haswell and later server platforms offer information about the sharing of resources.

To use the PSR monitoring service for a certain domain, a Resource Monitoring ID(RMID) is used to bind the domain to corresponding shared resource. RMID is a hardware-provided layer of abstraction between software and logical processors.

To use the PSR cache allocation service for a certain domain, a capacity bitmasks(CBM) is used to bind the domain to corresponding shared resource. CBM represents cache capacity and indicates the degree of overlap and isolation between domains. In hypervisor a Class of Service(COS) ID is allocated for each unique CBM.

The following resources are available:

1.2.138 pv-linear-pt (x86)

= <boolean>

Default: true

Only available if Xen is compiled with CONFIG_PV_LINEAR_PT support enabled.

Allow PV guests to have pagetable entries pointing to other pagetables of the same level (i.e., allowing L2 PTEs to point to other L2 pages). This technique is often called "linear pagetables", and is sometimes used to allow operating systems a simple way to consistently map the current process's pagetables into its own virtual address space.

Linux and MiniOS don't use this technique. NetBSD and Novell Netware do; there may be other custom operating systems which do. If you're certain you don't plan on having PV guests which use this feature, turning it off can reduce the attack surface.

1.2.139 pv-l1tf (x86)

= List of [ <bool>, dom0=<bool>, domu=<bool> ]

Default: false on believed-unaffected hardware, or in pv-shim mode. domu on believed-affected hardware.

Mitigations for L1TF / XSA-273 / CVE-2018-3620 for PV guests.

For backwards compatibility, we may not alter an architecturally-legitimate pagetable entry a PV guest chooses to write. We can however force such a guest into shadow mode so that Xen controls the PTEs which are reachable by the CPU pagewalk.

Shadowing is performed at the point where a PV guest first tries to write an L1TF-vulnerable PTE. Therefore, a PV guest kernel which has been updated with its own L1TF mitigations will not trigger shadow mode if it is well behaved.

If CONFIG_SHADOW_PAGING is not compiled in, this mitigation instead crashes the guest when an L1TF-vulnerable PTE is written, which still allows updated, well-behaved PV guests to run, despite Shadow being compiled out.

In the pv-shim case, Shadow is expected to be compiled out, and a malicious guest kernel can only leak data from the shim Xen, rather than the host Xen.

1.2.140 pv-shim (x86)

= <boolean>

Default: false

This option is intended for use by a toolstack, when choosing to run a PV guest compatibly inside an HVM container.

In this mode, the kernel and initrd passed as modules to the hypervisor are constructed into a plain unprivileged PV domain.

1.2.141 rcu-idle-timer-period-ms

= <integer>

Default: 10

How frequently a CPU which has gone idle, but with pending RCU callbacks, should be woken up to check if the grace period has completed, and the callbacks are safe to be executed. Expressed in milliseconds; maximum is 100, and it can't be 0.

1.2.142 reboot (x86)

= t[riple] | k[bd] | a[cpi] | p[ci] | P[ower] | e[fi] | n[o] [, [w]arm | [c]old]

Default: 0

Specify the host reboot method.

warm instructs Xen to not set the cold reboot flag.

cold instructs Xen to set the cold reboot flag.

no instructs Xen to not automatically reboot after panics or crashes.

triple instructs Xen to reboot the host by causing a triple fault.

kbd instructs Xen to reboot the host via the keyboard controller.

acpi instructs Xen to reboot the host using RESET_REG in the ACPI FADT.

pci instructs Xen to reboot the host using PCI reset register (port CF9).

Power instructs Xen to power-cycle the host using PCI reset register (port CF9).

'efi' instructs Xen to reboot using the EFI reboot call (in EFI mode by default it will use that method first).

xen instructs Xen to reboot using Xen's SCHEDOP hypercall (this is the default when running nested Xen)

1.2.143 rmrr

= start<-end>=[s1]bdf1[,[s1]bdf2[,...]];start<-end>=[s2]bdf1[,[s2]bdf2[,...]]

Define RMRR units that are missing from ACPI table along with device they belong to and use them for 1:1 mapping. End addresses can be omitted and one page will be mapped. The ranges are inclusive when start and end are specified. If segment of the first device is not specified, segment zero will be used. If other segments are not specified, first device segment will be used. If a segment is specified for other than the first device and it does not match the one specified for the first one, an error will be reported.

'start' and 'end' values are page numbers (not full physical addresses), in hexadecimal format (can optionally be preceded by "0x").

Usage example: If device 0:0:1d.0 requires one page (0xd5d45) to be reserved, and device 0:0:1a.0 requires three pages (0xd5d46 thru 0xd5d48) to be reserved, one usage would be:

rmrr=d5d45=0:0:1d.0;0xd5d46-0xd5d48=0:0:1a.0

Note: grub2 requires to escape or use quotations if special characters are used, namely ';', refer to the grub2 documentation if multiple ranges are specified.

1.2.144 ro-hpet (x86)

= <boolean>

Default: true

Map the HPET page as read only in Dom0. If disabled the page will be mapped with read and write permissions.

1.2.145 sched

= credit | credit2 | arinc653 | rtds | null

Default: sched=credit

Choose the default scheduler.

1.2.146 sched_credit2_migrate_resist

= <integer>

1.2.147 sched_credit_tslice_ms

= <integer>

Set the timeslice of the credit1 scheduler, in milliseconds. The default is 30ms. Reasonable values may include 10, 5, or even 1 for very latency-sensitive workloads.

1.2.148 sched_ratelimit_us

= <integer>

In order to limit the rate of context switching, set the minimum amount of time that a vcpu can be scheduled for before preempting it, in microseconds. The default is 1000us (1ms). Setting this to 0 disables it altogether.

1.2.149 sched_smt_power_savings

= <boolean>

Normally Xen will try to maximize performance and cache utilization by spreading out vcpus across as many different divisions as possible (i.e, numa nodes, sockets, cores threads, &c). This often maximizes throughput, but also maximizes energy usage, since it reduces the depth to which a processor can sleep.

This option inverts the logic, so that the scheduler in effect tries to keep the vcpus on the smallest amount of silicon possible; i.e., first fill up sibling threads, then sibling cores, then sibling sockets, &c. This will reduce performance somewhat, particularly on systems with hyperthreading enabled, but should reduce power by enabling more sockets and cores to go into deeper sleep states.

1.2.150 scrub-domheap

= <boolean>

Default: false

Scrub domains' freed pages. This is a safety net against a (buggy) domain accidentally leaking secrets by releasing pages without proper sanitization.

1.2.151 serial_tx_buffer

= <size>

Default: 16kB

Set the serial transmit buffer size.

1.2.152 serrors (ARM)

= diverse | forward | panic

Default: diverse

This parameter is provided to administrators to determine how the hypervisors handle SErrors.

In order to distinguish guest-generated SErrors from hypervisor-generated SErrors we have to place SError checking code in every EL1 <-> EL2 paths. That will cause overhead on entries and exits due to dsb/isb. However, not all platforms need to categorize SErrors. For example, a host that is running with trusted guests. The administrator can confirm that all guests that are running on the host will not trigger such SErrors. In this case, the administrator can use this parameter to skip categorizing SErrors and reduce the overhead of dsb/isb.

We provided the following 3 options to administrators to determine how the hypervisors handle SErrors:

  1. dsb/isb on all EL1 -> EL2 trap entries to categorize SErrors correctly.
  2. dsb/isb on EL2 -> EL1 return paths to prevent slipping hypervisor SErrors to guests.
  3. dsb/isb in context switch to isolate SErrors between 2 vCPUs.

1.2.153 shim_mem (x86)

= List of ( min:<size> | max:<size> | <size> )

Set the amount of memory that xen-shim uses. Only has effect if pv-shim mode is enabled. Note that this value accounts for the memory used by the shim itself plus the free memory slack given to the shim for runtime allocations.

By default, the amount of free memory slack given to the shim for runtime usage is 1MB.

1.2.154 smap (x86)

= <boolean> | hvm

Default: true

Flag to enable Supervisor Mode Access Prevention Use smap=hvm to allow SMAP use by HVM guests only.

1.2.155 smep (x86)

= <boolean> | hvm

Default: true

Flag to enable Supervisor Mode Execution Protection Use smep=hvm to allow SMEP use by HVM guests only.

1.2.156 smt (x86)

= <boolean>

Default: true

Control bring up of multiple hyper-threads per CPU core.

1.2.157 snb_igd_quirk

= <boolean> | cap | <integer>

A true boolean value enables legacy behavior (1s timeout), while cap enforces the maximum theoretically necessary timeout of 670ms. Any number is being interpreted as a custom timeout in milliseconds. Zero or boolean false disable the quirk workaround, which is also the default.

1.2.158 spec-ctrl (Arm)

= List of [ ssbd=force-disable|runtime|force-enable ]

Controls for speculative execution sidechannel mitigations.

The option ssbd= is used to control the state of Speculative Store Bypass Disable (SSBD) mitigation.

By default SSBD will be mitigated at runtime (i.e ssbd=runtime).

1.2.159 spec-ctrl (x86)

= List of [ <bool>, xen=<bool>, {pv,hvm,msr-sc,rsb,md-clear}=<bool>, bti-thunk=retpoline|lfence|jmp, {ibrs,ibpb,ssbd,eager-fpu, l1d-flush,l1tf-barrier}=<bool> ]

Controls for speculative execution sidechannel mitigations. By default, Xen will pick the most appropriate mitigations based on compiled in support, loaded microcode, and hardware details, and will virtualise appropriate mitigations for guests to use.

WARNING: Any use of this option may interfere with heuristics. Use with extreme care.

An overall boolean value, spec-ctrl=no, can be specified to turn off all mitigations, including pieces of infrastructure used to virtualise certain mitigation features for guests. This also includes settings which xpti, smt, pv-l1tf control, unless the respective option(s) have been specified earlier on the command line.

Alternatively, a slightly more restricted spec-ctrl=no-xen can be used to turn off all of Xen's mitigations, while leaving the virtualisation support in place for guests to use.

Use of a positive boolean value for either of these options is invalid.

The booleans pv=, hvm=, msr-sc=, rsb= and md-clear= offer fine grained control over the alternative blocks used by Xen. These impact Xen's ability to protect itself, and Xen's ability to virtualise support for guests to use.

If Xen was compiled with INDIRECT_THUNK support, bti-thunk= can be used to select which of the thunks gets patched into the __x86_indirect_thunk_%reg locations. The default thunk is retpoline (generally preferred for Intel hardware), with the alternatives being jmp (a jmp *%reg gadget, minimal overhead), and lfence (an lfence; jmp *%reg gadget, preferred for AMD).

On hardware supporting IBRS (Indirect Branch Restricted Speculation), the ibrs= option can be used to force or prevent Xen using the feature itself. If Xen is not using IBRS itself, functionality is still set up so IBRS can be virtualised for guests.

On hardware supporting IBPB (Indirect Branch Prediction Barrier), the ibpb= option can be used to force (the default) or prevent Xen from issuing branch prediction barriers on vcpu context switches.

On hardware supporting SSBD (Speculative Store Bypass Disable), the ssbd= option can be used to force or prevent Xen using the feature itself. On AMD hardware, this is a global option applied at boot, and not virtualised for guest use. On Intel hardware, the feature is virtualised for guests, independently of Xen's choice of setting.

On all hardware, the eager-fpu= option can be used to force or prevent Xen from using fully eager FPU context switches. This is currently implemented as a global control. By default, Xen will choose to use fully eager context switches on hardware believed to speculate past #NM exceptions.

On hardware supporting L1D_FLUSH, the l1d-flush= option can be used to force or prevent Xen from issuing an L1 data cache flush on each VMEntry. Irrespective of Xen's setting, the feature is virtualised for HVM guests to use. By default, Xen will enable this mitigation on hardware believed to be vulnerable to L1TF.

On hardware vulnerable to L1TF, the l1tf-barrier= option can be used to force or prevent Xen from protecting evaluations inside the hypervisor with a barrier instruction to not load potentially secret information into L1 cache. By default, Xen will enable this mitigation on hardware believed to be vulnerable to L1TF.

1.2.160 sync_console

= <boolean>

Default: false

Flag to force synchronous console output. Useful for debugging, but not suitable for production environments due to incurred overhead.

1.2.161 tboot (x86)

= 0x<phys_addr>

Specify the physical address of the trusted boot shared page.

1.2.162 tbuf_size

= <integer>

Specify the per-cpu trace buffer size in pages.

1.2.163 tdt (x86)

= <boolean>

Default: true

Flag to enable TSC deadline as the APIC timer mode.

1.2.164 tevt_mask

= <integer>

Specify a mask for Xen event tracing. This allows Xen tracing to be enabled at boot. Refer to the xentrace(8) documentation for a list of valid event mask values. In order to enable tracing, a buffer size (in pages) must also be specified via the tbuf_size parameter.

1.2.165 tickle_one_idle_cpu

= <boolean>

1.2.166 timer_slop

= <integer>

1.2.167 tsc (x86)

= unstable | skewed | stable:socket

1.2.168 ucode (x86)

= [<integer> | scan]

Specify how and where to find CPU microcode update blob.

'integer' specifies the CPU microcode update blob module index. When positive, this specifies the n-th module (in the GrUB entry, zero based) to be used for updating CPU micrcode. When negative, counting starts at the end of the modules in the GrUB entry (so with the blob commonly being last, one could specify ucode=-1). Note that the value of zero is not valid here (entry zero, i.e. the first module, is always the Dom0 kernel image). Note further that use of this option has an unspecified effect when used with xen.efi (there the concept of modules doesn't exist, and the blob gets specified via the ucode=<filename> config file/section entry; see EFI configuration file description).

'scan' instructs the hypervisor to scan the multiboot images for an cpio image that contains microcode. Depending on the platform the blob with the microcode in the cpio name space must be: - on Intel: kernel/x86/microcode/GenuineIntel.bin - on AMD : kernel/x86/microcode/AuthenticAMD.bin

1.2.169 unrestricted_guest (Intel)

= <boolean>

1.2.170 vcpu_migration_delay

= <integer>

Default: 0

Specify a delay, in microseconds, between migrations of a VCPU between PCPUs when using the credit1 scheduler. This prevents rapid fluttering of a VCPU between CPUs, and reduces the implicit overheads such as cache-warming. 1ms (1000) has been measured as a good value.

1.2.171 vesa-map

= <integer>

1.2.172 vesa-mtrr

= <integer>

1.2.173 vesa-ram

= <integer>

1.2.174 vga

= ( ask | current | text-80x<rows> | gfx-<width>x<height>x<depth> | mode-<mode> )[,keep]

ask causes Xen to display a menu of available modes and request the user to choose one of them.

current causes Xen to use the graphics adapter in its current state, without further setup.

text-80x<rows> instructs Xen to set up text mode. Valid values for <rows> are 25, 28, 30, 34, 43, 50, 80

gfx-<width>x<height>x<depth> instructs Xen to set up graphics mode with the specified width, height and depth.

mode-<mode> instructs Xen to use a specific mode, as shown with the ask option. (N.B menu modes are displayed in hex, so <mode> should be a hexadecimal number)

The optional keep parameter causes Xen to continue using the vga console even after dom0 has been started. The default behaviour is to relinquish control to dom0.

1.2.175 viridian-spinlock-retry-count (x86)

= <integer>

Default: 2047

Specify the maximum number of retries before an enlightened Windows guest will notify Xen that it has failed to acquire a spinlock.

1.2.176 viridian-version (x86)

= [<major>],[<minor>],[<build>]

Default: 6,0,0x1772

, and must be integers. The values will be encoded in guest CPUID 0x40000002 if viridian enlightenments are enabled.

1.2.177 vpid (Intel)

= <boolean>

Default: true

Use Virtual Processor ID support if available. This prevents the need for TLB flushes on VM entry and exit, increasing performance.

1.2.178 vpmu (x86)

= List of [ <bool>, bts, ipc, arch, rtm-abort=<bool> ]

Applicability: x86.  Default: false

Controls for Performance Monitoring Unit virtualisation.

Performance monitoring facilities tend to be very hardware specific, and provide access to a wealth of low level processor information.

Warning: As the virtualisation is not 100% safe, don't use the vpmu flag on production systems (see http://xenbits.xen.org/xsa/advisory-163.html)!

1.2.179 vwfi (arm)

= trap | native

Default: trap

WFI is the ARM instruction to "wait for interrupt". WFE is similar and means "wait for event". This option, which is ARM specific, changes the way guest WFI and WFE are implemented in Xen. By default, Xen traps both instructions. In the case of WFI, Xen blocks the guest vcpu; in the case of WFE, Xen yield the guest vcpu. When setting vwfi to native, Xen doesn't trap either instruction, running them in guest context. Setting vwfi to native reduces irq latency significantly. It can also lead to suboptimal scheduling decisions, but only when the system is oversubscribed (i.e., in total there are more vCPUs than pCPUs).

1.2.180 watchdog (x86)

= force | <boolean>

Default: false

Run an NMI watchdog on each processor. If a processor is stuck for longer than the watchdog_timeout, a panic occurs. When force is specified, in addition to running an NMI watchdog on each processor, unknown NMIs will still be processed.

1.2.181 watchdog_timeout (x86)

= <integer>

Default: 5

Set the NMI watchdog timeout in seconds. Specifying 0 will turn off the watchdog.

1.2.182 x2apic (x86)

= <boolean>

Default: true

Permit use of x2apic setup for SMP environments.

1.2.183 x2apic_phys (x86)

= <boolean>

Default: true if FADT mandates physical mode, false otherwise.

In the case that x2apic is in use, this option switches between physical and clustered mode. The default, given no hint from the FADT, is cluster mode.

1.2.184 xenheap_megabytes (arm32)

= <size>

Default: 0 (1/32 of RAM)

Amount of RAM to set aside for the Xenheap. Must be an integer multiple of 32.

By default will use 1/32 of the RAM up to a maximum of 1GB and with a minimum of 32M, subject to a suitably aligned and sized contiguous region of memory being available.

1.2.185 xpti (x86)

= List of [ default | <boolean> | dom0=<bool> | domu=<bool> ]

Default: false on hardware known not to be vulnerable to Meltdown (e.g. AMD) Default: true everywhere else

Override default selection of whether to isolate 64-bit PV guest page tables.

true activates page table isolation even on hardware not vulnerable by Meltdown for all domains.

false deactivates page table isolation on all systems for all domains.

default sets the default behaviour.

With dom0 and domu it is possible to control page table isolation for dom0 or guest domains only.

1.2.186 xsave (x86)

= <boolean>

Default: true

Permit use of the xsave/xrstor instructions.

1.2.187 xsm

= dummy | flask | silo

Default: selectable via Kconfig. Depends on enabled XSM modules.

Specify which XSM module should be enabled. This option is only available if the hypervisor was compiled with CONFIG_XSM enabled.