linux/Documentation/virtual/kvm/api.txt

The Definitive KVM (Kernel-based Virtual Machine) API Documentation
===================================================================

1. General description

The kvm API is a set of ioctls that are issued to control various aspects
of a virtual machine.  The ioctls belong to three classes

 - System ioctls: These query and set global attributes which affect the
   whole kvm subsystem.  In addition a system ioctl is used to create
   virtual machines

 - VM ioctls: These query and set attributes that affect an entire virtual
   machine, for example memory layout.  In addition a VM ioctl is used to
   create virtual cpus (vcpus).

   Only run VM ioctls from the same process (address space) that was used
   to create the VM.

 - vcpu ioctls: These query and set attributes that control the operation
   of a single virtual cpu.

   Only run vcpu ioctls from the same thread that was used to create the
   vcpu.

2. File descriptors

The kvm API is centered around file descriptors.  An initial
open("/dev/kvm") obtains a handle to the kvm subsystem; this handle
can be used to issue system ioctls.  A KVM_CREATE_VM ioctl on this
handle will create a VM file descriptor which can be used to issue VM
ioctls.  A KVM_CREATE_VCPU ioctl on a VM fd will create a virtual cpu
and return a file descriptor pointing to it.  Finally, ioctls on a vcpu
fd can be used to control the vcpu, including the important task of
actually running guest code.

In general file descriptors can be migrated among processes by means
of fork() and the SCM_RIGHTS facility of unix domain socket.  These
kinds of tricks are explicitly not supported by kvm.  While they will
not cause harm to the host, their actual behavior is not guaranteed by
the API.  The only supported use is one virtual machine per process,
and one vcpu per thread.

3. Extensions

As of Linux 2.6.22, the KVM ABI has been stabilized: no backward
incompatible change are allowed.  However, there is an extension
facility that allows backward-compatible extensions to the API to be
queried and used.

The extension mechanism is not based on on the Linux version number.
Instead, kvm defines extension identifiers and a facility to query
whether a particular extension identifier is available.  If it is, a
set of ioctls is available for application use.

4. API description

This section describes ioctls that can be used to control kvm guests.
For each ioctl, the following information is provided along with a
description:

  Capability: which KVM extension provides this ioctl.  Can be 'basic',
      which means that is will be provided by any kernel that supports
      API version 12 (see section 4.1), or a KVM_CAP_xyz constant, which
      means availability needs to be checked with KVM_CHECK_EXTENSION
      (see section 4.4).

  Architectures: which instruction set architectures provide this ioctl.
      x86 includes both i386 and x86_64.

  Type: system, vm, or vcpu.

  Parameters: what parameters are accepted by the ioctl.

  Returns: the return value.  General error numbers (EBADF, ENOMEM, EINVAL)
      are not detailed, but errors with specific meanings are.

4.1 KVM_GET_API_VERSION

Capability: basic
Architectures: all
Type: system ioctl
Parameters: none
Returns: the constant KVM_API_VERSION (=12)

This identifies the API version as the stable kvm API. It is not
expected that this number will change.  However, Linux 2.6.20 and
2.6.21 report earlier versions; these are not documented and not
supported.  Applications should refuse to run if KVM_GET_API_VERSION
returns a value other than 12.  If this check passes, all ioctls
described as 'basic' will be available.

4.2 KVM_CREATE_VM

Capability: basic
Architectures: all
Type: system ioctl
Parameters: none
Returns: a VM fd that can be used to control the new virtual machine.

The new VM has no virtual cpus and no memory.  An mmap() of a VM fd
will access the virtual machine's physical address space; offset zero
corresponds to guest physical address zero.  Use of mmap() on a VM fd
is discouraged if userspace memory allocation (KVM_CAP_USER_MEMORY) is
available.

4.3 KVM_GET_MSR_INDEX_LIST

Capability: basic
Architectures: x86
Type: system
Parameters: struct kvm_msr_list (in/out)
Returns: 0 on success; -1 on error
Errors:
  E2BIG:     the msr index list is to be to fit in the array specified by
             the user.

struct kvm_msr_list {
	__u32 nmsrs; /* number of msrs in entries */
	__u32 indices[0];
};

This ioctl returns the guest msrs that are supported.  The list varies
by kvm version and host processor, but does not change otherwise.  The
user fills in the size of the indices array in nmsrs, and in return
kvm adjusts nmsrs to reflect the actual number of msrs and fills in
the indices array with their numbers.

Note: if kvm indicates supports MCE (KVM_CAP_MCE), then the MCE bank MSRs are
not returned in the MSR list, as different vcpus can have a different number
of banks, as set via the KVM_X86_SETUP_MCE ioctl.

4.4 KVM_CHECK_EXTENSION

Capability: basic
Architectures: all
Type: system ioctl
Parameters: extension identifier (KVM_CAP_*)
Returns: 0 if unsupported; 1 (or some other positive integer) if supported

The API allows the application to query about extensions to the core
kvm API.  Userspace passes an extension identifier (an integer) and
receives an integer that describes the extension availability.
Generally 0 means no and 1 means yes, but some extensions may report
additional information in the integer return value.

4.5 KVM_GET_VCPU_MMAP_SIZE

Capability: basic
Architectures: all
Type: system ioctl
Parameters: none
Returns: size of vcpu mmap area, in bytes

The KVM_RUN ioctl (cf.) communicates with userspace via a shared
memory region.  This ioctl returns the size of that region.  See the
KVM_RUN documentation for details.

4.6 KVM_SET_MEMORY_REGION

Capability: basic
Architectures: all
Type: vm ioctl
Parameters: struct kvm_memory_region (in)
Returns: 0 on success, -1 on error

This ioctl is obsolete and has been removed.

4.7 KVM_CREATE_VCPU

Capability: basic
Architectures: all
Type: vm ioctl
Parameters: vcpu id (apic id on x86)
Returns: vcpu fd on success, -1 on error

This API adds a vcpu to a virtual machine.  The vcpu id is a small integer
in the range [0, max_vcpus).  You can use KVM_CAP_NR_VCPUS of the
KVM_CHECK_EXTENSION ioctl() to determine the value for max_vcpus at run-time.
If the KVM_CAP_NR_VCPUS does not exist, you should assume that max_vcpus is 4
cpus max.

On powerpc using book3s_hv mode, the vcpus are mapped onto virtual
threads in one or more virtual CPU cores.  (This is because the
hardware requires all the hardware threads in a CPU core to be in the
same partition.)  The KVM_CAP_PPC_SMT capability indicates the number
of vcpus per virtual core (vcore).  The vcore id is obtained by
dividing the vcpu id by the number of vcpus per vcore.  The vcpus in a
given vcore will always be in the same physical core as each other
(though that might be a different physical core from time to time).
Userspace can control the threading (SMT) mode of the guest by its
allocation of vcpu ids.  For example, if userspace wants
single-threaded guest vcpus, it should make all vcpu ids be a multiple
of the number of vcpus per vcore.

4.8 KVM_GET_DIRTY_LOG (vm ioctl)

Capability: basic
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_dirty_log (in/out)
Returns: 0 on success, -1 on error

/* for KVM_GET_DIRTY_LOG */
struct kvm_dirty_log {
	__u32 slot;
	__u32 padding;
	union {
		void __user *dirty_bitmap; /* one bit per page */
		__u64 padding;
	};
};

Given a memory slot, return a bitmap containing any pages dirtied
since the last call to this ioctl.  Bit 0 is the first page in the
memory slot.  Ensure the entire structure is cleared to avoid padding
issues.

4.9 KVM_SET_MEMORY_ALIAS

Capability: basic
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_memory_alias (in)
Returns: 0 (success), -1 (error)

This ioctl is obsolete and has been removed.

4.10 KVM_RUN

Capability: basic
Architectures: all
Type: vcpu ioctl
Parameters: none
Returns: 0 on success, -1 on error
Errors:
  EINTR:     an unmasked signal is pending

This ioctl is used to run a guest virtual cpu.  While there are no
explicit parameters, there is an implicit parameter block that can be
obtained by mmap()ing the vcpu fd at offset 0, with the size given by
KVM_GET_VCPU_MMAP_SIZE.  The parameter block is formatted as a 'struct
kvm_run' (see below).

4.11 KVM_GET_REGS

Capability: basic
Architectures: all
Type: vcpu ioctl
Parameters: struct kvm_regs (out)
Returns: 0 on success, -1 on error

Reads the general purpose registers from the vcpu.

/* x86 */
struct kvm_regs {
	/* out (KVM_GET_REGS) / in (KVM_SET_REGS) */
	__u64 rax, rbx, rcx, rdx;
	__u64 rsi, rdi, rsp, rbp;
	__u64 r8,  r9,  r10, r11;
	__u64 r12, r13, r14, r15;
	__u64 rip, rflags;
};

4.12 KVM_SET_REGS

Capability: basic
Architectures: all
Type: vcpu ioctl
Parameters: struct kvm_regs (in)
Returns: 0 on success, -1 on error

Writes the general purpose registers into the vcpu.

See KVM_GET_REGS for the data structure.

4.13 KVM_GET_SREGS

Capability: basic
Architectures: x86, ppc
Type: vcpu ioctl
Parameters: struct kvm_sregs (out)
Returns: 0 on success, -1 on error

Reads special registers from the vcpu.

/* x86 */
struct kvm_sregs {
	struct kvm_segment cs, ds, es, fs, gs, ss;
	struct kvm_segment tr, ldt;
	struct kvm_dtable gdt, idt;
	__u64 cr0, cr2, cr3, cr4, cr8;
	__u64 efer;
	__u64 apic_base;
	__u64 interrupt_bitmap[(KVM_NR_INTERRUPTS + 63) / 64];
};

/* ppc -- see arch/powerpc/include/asm/kvm.h */

interrupt_bitmap is a bitmap of pending external interrupts.  At most
one bit may be set.  This interrupt has been acknowledged by the APIC
but not yet injected into the cpu core.

4.14 KVM_SET_SREGS

Capability: basic
Architectures: x86, ppc
Type: vcpu ioctl
Parameters: struct kvm_sregs (in)
Returns: 0 on success, -1 on error

Writes special registers into the vcpu.  See KVM_GET_SREGS for the
data structures.

4.15 KVM_TRANSLATE

Capability: basic
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_translation (in/out)
Returns: 0 on success, -1 on error

Translates a virtual address according to the vcpu's current address
translation mode.

struct kvm_translation {
	/* in */
	__u64 linear_address;

	/* out */
	__u64 physical_address;
	__u8  valid;
	__u8  writeable;
	__u8  usermode;
	__u8  pad[5];
};

4.16 KVM_INTERRUPT

Capability: basic
Architectures: x86, ppc
Type: vcpu ioctl
Parameters: struct kvm_interrupt (in)
Returns: 0 on success, -1 on error

Queues a hardware interrupt vector to be injected.  This is only
useful if in-kernel local APIC or equivalent is not used.

/* for KVM_INTERRUPT */
struct kvm_interrupt {
	/* in */
	__u32 irq;
};

X86:

Note 'irq' is an interrupt vector, not an interrupt pin or line.

PPC:

Queues an external interrupt to be injected. This ioctl is overleaded
with 3 different irq values:

a) KVM_INTERRUPT_SET

  This injects an edge type external interrupt into the guest once it's ready
  to receive interrupts. When injected, the interrupt is done.

b) KVM_INTERRUPT_UNSET

  This unsets any pending interrupt.

  Only available with KVM_CAP_PPC_UNSET_IRQ.

c) KVM_INTERRUPT_SET_LEVEL

  This injects a level type external interrupt into the guest context. The
  interrupt stays pending until a specific ioctl with KVM_INTERRUPT_UNSET
  is triggered.

  Only available with KVM_CAP_PPC_IRQ_LEVEL.

Note that any value for 'irq' other than the ones stated above is invalid
and incurs unexpected behavior.

4.17 KVM_DEBUG_GUEST

Capability: basic
Architectures: none
Type: vcpu ioctl
Parameters: none)
Returns: -1 on error

Support for this has been removed.  Use KVM_SET_GUEST_DEBUG instead.

4.18 KVM_GET_MSRS

Capability: basic
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_msrs (in/out)
Returns: 0 on success, -1 on error

Reads model-specific registers from the vcpu.  Supported msr indices can
be obtained using KVM_GET_MSR_INDEX_LIST.

struct kvm_msrs {
	__u32 nmsrs; /* number of msrs in entries */
	__u32 pad;

	struct kvm_msr_entry entries[0];
};

struct kvm_msr_entry {
	__u32 index;
	__u32 reserved;
	__u64 data;
};

Application code should set the 'nmsrs' member (which indicates the
size of the entries array) and the 'index' member of each array entry.
kvm will fill in the 'data' member.

4.19 KVM_SET_MSRS

Capability: basic
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_msrs (in)
Returns: 0 on success, -1 on error

Writes model-specific registers to the vcpu.  See KVM_GET_MSRS for the
data structures.

Application code should set the 'nmsrs' member (which indicates the
size of the entries array), and the 'index' and 'data' members of each
array entry.

4.20 KVM_SET_CPUID

Capability: basic
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_cpuid (in)
Returns: 0 on success, -1 on error

Defines the vcpu responses to the cpuid instruction.  Applications
should use the KVM_SET_CPUID2 ioctl if available.


struct kvm_cpuid_entry {
	__u32 function;
	__u32 eax;
	__u32 ebx;
	__u32 ecx;
	__u32 edx;
	__u32 padding;
};

/* for KVM_SET_CPUID */
struct kvm_cpuid {
	__u32 nent;
	__u32 padding;
	struct kvm_cpuid_entry entries[0];
};

4.21 KVM_SET_SIGNAL_MASK

Capability: basic
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_signal_mask (in)
Returns: 0 on success, -1 on error

Defines which signals are blocked during execution of KVM_RUN.  This
signal mask temporarily overrides the threads signal mask.  Any
unblocked signal received (except SIGKILL and SIGSTOP, which retain
their traditional behaviour) will cause KVM_RUN to return with -EINTR.

Note the signal will only be delivered if not blocked by the original
signal mask.

/* for KVM_SET_SIGNAL_MASK */
struct kvm_signal_mask {
	__u32 len;
	__u8  sigset[0];
};

4.22 KVM_GET_FPU

Capability: basic
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_fpu (out)
Returns: 0 on success, -1 on error

Reads the floating point state from the vcpu.

/* for KVM_GET_FPU and KVM_SET_FPU */
struct kvm_fpu {
	__u8  fpr[8][16];
	__u16 fcw;
	__u16 fsw;
	__u8  ftwx;  /* in fxsave format */
	__u8  pad1;
	__u16 last_opcode;
	__u64 last_ip;
	__u64 last_dp;
	__u8  xmm[16][16];
	__u32 mxcsr;
	__u32 pad2;
};

4.23 KVM_SET_FPU

Capability: basic
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_fpu (in)
Returns: 0 on success, -1 on error

Writes the floating point state to the vcpu.

/* for KVM_GET_FPU and KVM_SET_FPU */
struct kvm_fpu {
	__u8  fpr[8][16];
	__u16 fcw;
	__u16 fsw;
	__u8  ftwx;  /* in fxsave format */
	__u8  pad1;
	__u16 last_opcode;
	__u64 last_ip;
	__u64 last_dp;
	__u8  xmm[16][16];
	__u32 mxcsr;
	__u32 pad2;
};

4.24 KVM_CREATE_IRQCHIP

Capability: KVM_CAP_IRQCHIP
Architectures: x86, ia64
Type: vm ioctl
Parameters: none
Returns: 0 on success, -1 on error

Creates an interrupt controller model in the kernel.  On x86, creates a virtual
ioapic, a virtual PIC (two PICs, nested), and sets up future vcpus to have a
local APIC.  IRQ routing for GSIs 0-15 is set to both PIC and IOAPIC; GSI 16-23
only go to the IOAPIC.  On ia64, a IOSAPIC is created.

4.25 KVM_IRQ_LINE

Capability: KVM_CAP_IRQCHIP
Architectures: x86, ia64
Type: vm ioctl
Parameters: struct kvm_irq_level
Returns: 0 on success, -1 on error

Sets the level of a GSI input to the interrupt controller model in the kernel.
Requires that an interrupt controller model has been previously created with
KVM_CREATE_IRQCHIP.  Note that edge-triggered interrupts require the level
to be set to 1 and then back to 0.

struct kvm_irq_level {
	union {
		__u32 irq;     /* GSI */
		__s32 status;  /* not used for KVM_IRQ_LEVEL */
	};
	__u32 level;           /* 0 or 1 */
};

4.26 KVM_GET_IRQCHIP

Capability: KVM_CAP_IRQCHIP
Architectures: x86, ia64
Type: vm ioctl
Parameters: struct kvm_irqchip (in/out)
Returns: 0 on success, -1 on error

Reads the state of a kernel interrupt controller created with
KVM_CREATE_IRQCHIP into a buffer provided by the caller.

struct kvm_irqchip {
	__u32 chip_id;  /* 0 = PIC1, 1 = PIC2, 2 = IOAPIC */
	__u32 pad;
        union {
		char dummy[512];  /* reserving space */
		struct kvm_pic_state pic;
		struct kvm_ioapic_state ioapic;
	} chip;
};

4.27 KVM_SET_IRQCHIP

Capability: KVM_CAP_IRQCHIP
Architectures: x86, ia64
Type: vm ioctl
Parameters: struct kvm_irqchip (in)
Returns: 0 on success, -1 on error

Sets the state of a kernel interrupt controller created with
KVM_CREATE_IRQCHIP from a buffer provided by the caller.

struct kvm_irqchip {
	__u32 chip_id;  /* 0 = PIC1, 1 = PIC2, 2 = IOAPIC */
	__u32 pad;
        union {
		char dummy[512];  /* reserving space */
		struct kvm_pic_state pic;
		struct kvm_ioapic_state ioapic;
	} chip;
};

4.28 KVM_XEN_HVM_CONFIG

Capability: KVM_CAP_XEN_HVM
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_xen_hvm_config (in)
Returns: 0 on success, -1 on error

Sets the MSR that the Xen HVM guest uses to initialize its hypercall
page, and provides the starting address and size of the hypercall
blobs in userspace.  When the guest writes the MSR, kvm copies one
page of a blob (32- or 64-bit, depending on the vcpu mode) to guest
memory.

struct kvm_xen_hvm_config {
	__u32 flags;
	__u32 msr;
	__u64 blob_addr_32;
	__u64 blob_addr_64;
	__u8 blob_size_32;
	__u8 blob_size_64;
	__u8 pad2[30];
};

4.29 KVM_GET_CLOCK

Capability: KVM_CAP_ADJUST_CLOCK
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_clock_data (out)
Returns: 0 on success, -1 on error

Gets the current timestamp of kvmclock as seen by the current guest. In
conjunction with KVM_SET_CLOCK, it is used to ensure monotonicity on scenarios
such as migration.

struct kvm_clock_data {
	__u64 clock;  /* kvmclock current value */
	__u32 flags;
	__u32 pad[9];
};

4.30 KVM_SET_CLOCK

Capability: KVM_CAP_ADJUST_CLOCK
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_clock_data (in)
Returns: 0 on success, -1 on error

Sets the current timestamp of kvmclock to the value specified in its parameter.
In conjunction with KVM_GET_CLOCK, it is used to ensure monotonicity on scenarios
such as migration.

struct kvm_clock_data {
	__u64 clock;  /* kvmclock current value */
	__u32 flags;
	__u32 pad[9];
};

4.31 KVM_GET_VCPU_EVENTS

Capability: KVM_CAP_VCPU_EVENTS
Extended by: KVM_CAP_INTR_SHADOW
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_vcpu_event (out)
Returns: 0 on success, -1 on error

Gets currently pending exceptions, interrupts, and NMIs as well as related
states of the vcpu.

struct kvm_vcpu_events {
	struct {
		__u8 injected;
		__u8 nr;
		__u8 has_error_code;
		__u8 pad;
		__u32 error_code;
	} exception;
	struct {
		__u8 injected;
		__u8 nr;
		__u8 soft;
		__u8 shadow;
	} interrupt;
	struct {
		__u8 injected;
		__u8 pending;
		__u8 masked;
		__u8 pad;
	} nmi;
	__u32 sipi_vector;
	__u32 flags;
};

KVM_VCPUEVENT_VALID_SHADOW may be set in the flags field to signal that
interrupt.shadow contains a valid state. Otherwise, this field is undefined.

4.32 KVM_SET_VCPU_EVENTS

Capability: KVM_CAP_VCPU_EVENTS
Extended by: KVM_CAP_INTR_SHADOW
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_vcpu_event (in)
Returns: 0 on success, -1 on error

Set pending exceptions, interrupts, and NMIs as well as related states of the
vcpu.

See KVM_GET_VCPU_EVENTS for the data structure.

Fields that may be modified asynchronously by running VCPUs can be excluded
from the update. These fields are nmi.pending and sipi_vector. Keep the
corresponding bits in the flags field cleared to suppress overwriting the
current in-kernel state. The bits are:

KVM_VCPUEVENT_VALID_NMI_PENDING - transfer nmi.pending to the kernel
KVM_VCPUEVENT_VALID_SIPI_VECTOR - transfer sipi_vector

If KVM_CAP_INTR_SHADOW is available, KVM_VCPUEVENT_VALID_SHADOW can be set in
the flags field to signal that interrupt.shadow contains a valid state and
shall be written into the VCPU.

4.33 KVM_GET_DEBUGREGS

Capability: KVM_CAP_DEBUGREGS
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_debugregs (out)
Returns: 0 on success, -1 on error

Reads debug registers from the vcpu.

struct kvm_debugregs {
	__u64 db[4];
	__u64 dr6;
	__u64 dr7;
	__u64 flags;
	__u64 reserved[9];
};

4.34 KVM_SET_DEBUGREGS

Capability: KVM_CAP_DEBUGREGS
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_debugregs (in)
Returns: 0 on success, -1 on error

Writes debug registers into the vcpu.

See KVM_GET_DEBUGREGS for the data structure. The flags field is unused
yet and must be cleared on entry.

4.35 KVM_SET_USER_MEMORY_REGION

Capability: KVM_CAP_USER_MEM
Architectures: all
Type: vm ioctl
Parameters: struct kvm_userspace_memory_region (in)
Returns: 0 on success, -1 on error

struct kvm_userspace_memory_region {
	__u32 slot;
	__u32 flags;
	__u64 guest_phys_addr;
	__u64 memory_size; /* bytes */
	__u64 userspace_addr; /* start of the userspace allocated memory */
};

/* for kvm_memory_region::flags */
#define KVM_MEM_LOG_DIRTY_PAGES  1UL

This ioctl allows the user to create or modify a guest physical memory
slot.  When changing an existing slot, it may be moved in the guest
physical memory space, or its flags may be modified.  It may not be
resized.  Slots may not overlap in guest physical address space.

Memory for the region is taken starting at the address denoted by the
field userspace_addr, which must point at user addressable memory for
the entire memory slot size.  Any object may back this memory, including
anonymous memory, ordinary files, and hugetlbfs.

It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr
be identical.  This allows large pages in the guest to be backed by large
pages in the host.

The flags field supports just one flag, KVM_MEM_LOG_DIRTY_PAGES, which
instructs kvm to keep track of writes to memory within the slot.  See
the KVM_GET_DIRTY_LOG ioctl.

When the KVM_CAP_SYNC_MMU capability, changes in the backing of the memory
region are automatically reflected into the guest.  For example, an mmap()
that affects the region will be made visible immediately.  Another example
is madvise(MADV_DROP).

It is recommended to use this API instead of the KVM_SET_MEMORY_REGION ioctl.
The KVM_SET_MEMORY_REGION does not allow fine grained control over memory
allocation and is deprecated.

4.36 KVM_SET_TSS_ADDR

Capability: KVM_CAP_SET_TSS_ADDR
Architectures: x86
Type: vm ioctl
Parameters: unsigned long tss_address (in)
Returns: 0 on success, -1 on error

This ioctl defines the physical address of a three-page region in the guest
physical address space.  The region must be within the first 4GB of the
guest physical address space and must not conflict with any memory slot
or any mmio address.  The guest may malfunction if it accesses this memory
region.

This ioctl is required on Intel-based hosts.  This is needed on Intel hardware
because of a quirk in the virtualization implementation (see the internals
documentation when it pops into existence).

4.37 KVM_ENABLE_CAP

Capability: KVM_CAP_ENABLE_CAP
Architectures: ppc
Type: vcpu ioctl
Parameters: struct kvm_enable_cap (in)
Returns: 0 on success; -1 on error

+Not all extensions are enabled by default. Using this ioctl the application
can enable an extension, making it available to the guest.

On systems that do not support this ioctl, it always fails. On systems that
do support it, it only works for extensions that are supported for enablement.

To check if a capability can be enabled, the KVM_CHECK_EXTENSION ioctl should
be used.

struct kvm_enable_cap {
       /* in */
       __u32 cap;

The capability that is supposed to get enabled.

       __u32 flags;

A bitfield indicating future enhancements. Has to be 0 for now.

       __u64 args[4];

Arguments for enabling a feature. If a feature needs initial values to
function properly, this is the place to put them.

       __u8  pad[64];
};

4.38 KVM_GET_MP_STATE

Capability: KVM_CAP_MP_STATE
Architectures: x86, ia64
Type: vcpu ioctl
Parameters: struct kvm_mp_state (out)
Returns: 0 on success; -1 on error

struct kvm_mp_state {
	__u32 mp_state;
};

Returns the vcpu's current "multiprocessing state" (though also valid on
uniprocessor guests).

Possible values are:

 - KVM_MP_STATE_RUNNABLE:        the vcpu is currently running
 - KVM_MP_STATE_UNINITIALIZED:   the vcpu is an application processor (AP)
                                 which has not yet received an INIT signal
 - KVM_MP_STATE_INIT_RECEIVED:   the vcpu has received an INIT signal, and is
                                 now ready for a SIPI
 - KVM_MP_STATE_HALTED:          the vcpu has executed a HLT instruction and
                                 is waiting for an interrupt
 - KVM_MP_STATE_SIPI_RECEIVED:   the vcpu has just received a SIPI (vector
                                 accessible via KVM_GET_VCPU_EVENTS)

This ioctl is only useful after KVM_CREATE_IRQCHIP.  Without an in-kernel
irqchip, the multiprocessing state must be maintained by userspace.

4.39 KVM_SET_MP_STATE

Capability: KVM_CAP_MP_STATE
Architectures: x86, ia64
Type: vcpu ioctl
Parameters: struct kvm_mp_state (in)
Returns: 0 on success; -1 on error

Sets the vcpu's current "multiprocessing state"; see KVM_GET_MP_STATE for
arguments.

This ioctl is only useful after KVM_CREATE_IRQCHIP.  Without an in-kernel
irqchip, the multiprocessing state must be maintained by userspace.

4.40 KVM_SET_IDENTITY_MAP_ADDR

Capability: KVM_CAP_SET_IDENTITY_MAP_ADDR
Architectures: x86
Type: vm ioctl
Parameters: unsigned long identity (in)
Returns: 0 on success, -1 on error

This ioctl defines the physical address of a one-page region in the guest
physical address space.  The region must be within the first 4GB of the
guest physical address space and must not conflict with any memory slot
or any mmio address.  The guest may malfunction if it accesses this memory
region.

This ioctl is required on Intel-based hosts.  This is needed on Intel hardware
because of a quirk in the virtualization implementation (see the internals
documentation when it pops into existence).

4.41 KVM_SET_BOOT_CPU_ID

Capability: KVM_CAP_SET_BOOT_CPU_ID
Architectures: x86, ia64
Type: vm ioctl
Parameters: unsigned long vcpu_id
Returns: 0 on success, -1 on error

Define which vcpu is the Bootstrap Processor (BSP).  Values are the same
as the vcpu id in KVM_CREATE_VCPU.  If this ioctl is not called, the default
is vcpu 0.

4.42 KVM_GET_XSAVE

Capability: KVM_CAP_XSAVE
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_xsave (out)
Returns: 0 on success, -1 on error

struct kvm_xsave {
	__u32 region[1024];
};

This ioctl would copy current vcpu's xsave struct to the userspace.

4.43 KVM_SET_XSAVE

Capability: KVM_CAP_XSAVE
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_xsave (in)
Returns: 0 on success, -1 on error

struct kvm_xsave {
	__u32 region[1024];
};

This ioctl would copy userspace's xsave struct to the kernel.

4.44 KVM_GET_XCRS

Capability: KVM_CAP_XCRS
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_xcrs (out)
Returns: 0 on success, -1 on error

struct kvm_xcr {
	__u32 xcr;
	__u32 reserved;
	__u64 value;
};

struct kvm_xcrs {
	__u32 nr_xcrs;
	__u32 flags;
	struct kvm_xcr xcrs[KVM_MAX_XCRS];
	__u64 padding[16];
};

This ioctl would copy current vcpu's xcrs to the userspace.

4.45 KVM_SET_XCRS

Capability: KVM_CAP_XCRS
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_xcrs (in)
Returns: 0 on success, -1 on error

struct kvm_xcr {
	__u32 xcr;
	__u32 reserved;
	__u64 value;
};

struct kvm_xcrs {
	__u32 nr_xcrs;
	__u32 flags;
	struct kvm_xcr xcrs[KVM_MAX_XCRS];
	__u64 padding[16];
};

This ioctl would set vcpu's xcr to the value userspace specified.

4.46 KVM_GET_SUPPORTED_CPUID

Capability: KVM_CAP_EXT_CPUID
Architectures: x86
Type: system ioctl
Parameters: struct kvm_cpuid2 (in/out)
Returns: 0 on success, -1 on error

struct kvm_cpuid2 {
	__u32 nent;
	__u32 padding;
	struct kvm_cpuid_entry2 entries[0];
};

#define KVM_CPUID_FLAG_SIGNIFCANT_INDEX 1
#define KVM_CPUID_FLAG_STATEFUL_FUNC    2
#define KVM_CPUID_FLAG_STATE_READ_NEXT  4

struct kvm_cpuid_entry2 {
	__u32 function;
	__u32 index;
	__u32 flags;
	__u32 eax;
	__u32 ebx;
	__u32 ecx;
	__u32 edx;
	__u32 padding[3];
};

This ioctl returns x86 cpuid features which are supported by both the hardware
and kvm.  Userspace can use the information returned by this ioctl to
construct cpuid information (for KVM_SET_CPUID2) that is consistent with
hardware, kernel, and userspace capabilities, and with user requirements (for
example, the user may wish to constrain cpuid to emulate older hardware,
or for feature consistency across a cluster).

Userspace invokes KVM_GET_SUPPORTED_CPUID by passing a kvm_cpuid2 structure
with the 'nent' field indicating the number of entries in the variable-size
array 'entries'.  If the number of entries is too low to describe the cpu
capabilities, an error (E2BIG) is returned.  If the number is too high,
the 'nent' field is adjusted and an error (ENOMEM) is returned.  If the
number is just right, the 'nent' field is adjusted to the number of valid
entries in the 'entries' array, which is then filled.

The entries returned are the host cpuid as returned by the cpuid instruction,
with unknown or unsupported features masked out.  Some features (for example,
x2apic), may not be present in the host cpu, but are exposed by kvm if it can
emulate them efficiently. The fields in each entry are defined as follows:

  function: the eax value used to obtain the entry
  index: the ecx value used to obtain the entry (for entries that are
         affected by ecx)
  flags: an OR of zero or more of the following:
        KVM_CPUID_FLAG_SIGNIFCANT_INDEX:
           if the index field is valid
        KVM_CPUID_FLAG_STATEFUL_FUNC:
           if cpuid for this function returns different values for successive
           invocations; there will be several entries with the same function,
           all with this flag set
        KVM_CPUID_FLAG_STATE_READ_NEXT:
           for KVM_CPUID_FLAG_STATEFUL_FUNC entries, set if this entry is
           the first entry to be read by a cpu
   eax, ebx, ecx, edx: the values returned by the cpuid instruction for
         this function/index combination

4.47 KVM_PPC_GET_PVINFO

Capability: KVM_CAP_PPC_GET_PVINFO
Architectures: ppc
Type: vm ioctl
Parameters: struct kvm_ppc_pvinfo (out)
Returns: 0 on success, !0 on error

struct kvm_ppc_pvinfo {
	__u32 flags;
	__u32 hcall[4];
	__u8  pad[108];
};

This ioctl fetches PV specific information that need to be passed to the guest
using the device tree or other means from vm context.

For now the only implemented piece of information distributed here is an array
of 4 instructions that make up a hypercall.

If any additional field gets added to this structure later on, a bit for that
additional piece of information will be set in the flags bitmap.

4.48 KVM_ASSIGN_PCI_DEVICE

Capability: KVM_CAP_DEVICE_ASSIGNMENT
Architectures: x86 ia64
Type: vm ioctl
Parameters: struct kvm_assigned_pci_dev (in)
Returns: 0 on success, -1 on error

Assigns a host PCI device to the VM.

struct kvm_assigned_pci_dev {
	__u32 assigned_dev_id;
	__u32 busnr;
	__u32 devfn;
	__u32 flags;
	__u32 segnr;
	union {
		__u32 reserved[11];
	};
};

The PCI device is specified by the triple segnr, busnr, and devfn.
Identification in succeeding service requests is done via assigned_dev_id. The
following flags are specified:

/* Depends on KVM_CAP_IOMMU */
#define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)

4.49 KVM_DEASSIGN_PCI_DEVICE

Capability: KVM_CAP_DEVICE_DEASSIGNMENT
Architectures: x86 ia64
Type: vm ioctl
Parameters: struct kvm_assigned_pci_dev (in)
Returns: 0 on success, -1 on error

Ends PCI device assignment, releasing all associated resources.

See KVM_CAP_DEVICE_ASSIGNMENT for the data structure. Only assigned_dev_id is
used in kvm_assigned_pci_dev to identify the device.

4.50 KVM_ASSIGN_DEV_IRQ

Capability: KVM_CAP_ASSIGN_DEV_IRQ
Architectures: x86 ia64
Type: vm ioctl
Parameters: struct kvm_assigned_irq (in)
Returns: 0 on success, -1 on error

Assigns an IRQ to a passed-through device.

struct kvm_assigned_irq {
	__u32 assigned_dev_id;
	__u32 host_irq; /* ignored (legacy field) */
	__u32 guest_irq;
	__u32 flags;
	union {
		__u32 reserved[12];
	};
};

The following flags are defined:

#define KVM_DEV_IRQ_HOST_INTX    (1 << 0)
#define KVM_DEV_IRQ_HOST_MSI     (1 << 1)
#define KVM_DEV_IRQ_HOST_MSIX    (1 << 2)

#define KVM_DEV_IRQ_GUEST_INTX   (1 << 8)
#define KVM_DEV_IRQ_GUEST_MSI    (1 << 9)
#define KVM_DEV_IRQ_GUEST_MSIX   (1 << 10)

It is not valid to specify multiple types per host or guest IRQ. However, the
IRQ type of host and guest can differ or can even be null.

4.51 KVM_DEASSIGN_DEV_IRQ

Capability: KVM_CAP_ASSIGN_DEV_IRQ
Architectures: x86 ia64
Type: vm ioctl
Parameters: struct kvm_assigned_irq (in)
Returns: 0 on success, -1 on error

Ends an IRQ assignment to a passed-through device.

See KVM_ASSIGN_DEV_IRQ for the data structure. The target device is specified
by assigned_dev_id, flags must correspond to the IRQ type specified on
KVM_ASSIGN_DEV_IRQ. Partial deassignment of host or guest IRQ is allowed.

4.52 KVM_SET_GSI_ROUTING

Capability: KVM_CAP_IRQ_ROUTING
Architectures: x86 ia64
Type: vm ioctl
Parameters: struct kvm_irq_routing (in)
Returns: 0 on success, -1 on error

Sets the GSI routing table entries, overwriting any previously set entries.

struct kvm_irq_routing {
	__u32 nr;
	__u32 flags;
	struct kvm_irq_routing_entry entries[0];
};

No flags are specified so far, the corresponding field must be set to zero.

struct kvm_irq_routing_entry {
	__u32 gsi;
	__u32 type;
	__u32 flags;
	__u32 pad;
	union {
		struct kvm_irq_routing_irqchip irqchip;
		struct kvm_irq_routing_msi msi;
		__u32 pad[8];
	} u;
};

/* gsi routing entry types */
#define KVM_IRQ_ROUTING_IRQCHIP 1
#define KVM_IRQ_ROUTING_MSI 2

No flags are specified so far, the corresponding field must be set to zero.

struct kvm_irq_routing_irqchip {
	__u32 irqchip;
	__u32 pin;
};

struct kvm_irq_routing_msi {
	__u32 address_lo;
	__u32 address_hi;
	__u32 data;
	__u32 pad;
};

4.53 KVM_ASSIGN_SET_MSIX_NR

Capability: KVM_CAP_DEVICE_MSIX
Architectures: x86 ia64
Type: vm ioctl
Parameters: struct kvm_assigned_msix_nr (in)
Returns: 0 on success, -1 on error

Set the number of MSI-X interrupts for an assigned device. The number is
reset again by terminating the MSI-X assignment of the device via
KVM_DEASSIGN_DEV_IRQ. Calling this service more than once at any earlier
point will fail.

struct kvm_assigned_msix_nr {
	__u32 assigned_dev_id;
	__u16 entry_nr;
	__u16 padding;
};

#define KVM_MAX_MSIX_PER_DEV		256

4.54 KVM_ASSIGN_SET_MSIX_ENTRY

Capability: KVM_CAP_DEVICE_MSIX
Architectures: x86 ia64
Type: vm ioctl
Parameters: struct kvm_assigned_msix_entry (in)
Returns: 0 on success, -1 on error

Specifies the routing of an MSI-X assigned device interrupt to a GSI. Setting
the GSI vector to zero means disabling the interrupt.

struct kvm_assigned_msix_entry {
	__u32 assigned_dev_id;
	__u32 gsi;
	__u16 entry; /* The index of entry in the MSI-X table */
	__u16 padding[3];
};

4.54 KVM_SET_TSC_KHZ

Capability: KVM_CAP_TSC_CONTROL
Architectures: x86
Type: vcpu ioctl
Parameters: virtual tsc_khz
Returns: 0 on success, -1 on error

Specifies the tsc frequency for the virtual machine. The unit of the
frequency is KHz.

4.55 KVM_GET_TSC_KHZ

Capability: KVM_CAP_GET_TSC_KHZ
Architectures: x86
Type: vcpu ioctl
Parameters: none
Returns: virtual tsc-khz on success, negative value on error

Returns the tsc frequency of the guest. The unit of the return value is
KHz. If the host has unstable tsc this ioctl returns -EIO instead as an
error.

4.56 KVM_GET_LAPIC

Capability: KVM_CAP_IRQCHIP
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_lapic_state (out)
Returns: 0 on success, -1 on error

#define KVM_APIC_REG_SIZE 0x400
struct kvm_lapic_state {
	char regs[KVM_APIC_REG_SIZE];
};

Reads the Local APIC registers and copies them into the input argument.  The
data format and layout are the same as documented in the architecture manual.

4.57 KVM_SET_LAPIC

Capability: KVM_CAP_IRQCHIP
Architectures: x86
Type: vcpu ioctl
Parameters: struct kvm_lapic_state (in)
Returns: 0 on success, -1 on error

#define KVM_APIC_REG_SIZE 0x400
struct kvm_lapic_state {
	char regs[KVM_APIC_REG_SIZE];
};

Copies the input argument into the the Local APIC registers.  The data format
and layout are the same as documented in the architecture manual.

4.58 KVM_IOEVENTFD

Capability: KVM_CAP_IOEVENTFD
Architectures: all
Type: vm ioctl
Parameters: struct kvm_ioeventfd (in)
Returns: 0 on success, !0 on error

This ioctl attaches or detaches an ioeventfd to a legal pio/mmio address
within the guest.  A guest write in the registered address will signal the
provided event instead of triggering an exit.

struct kvm_ioeventfd {
	__u64 datamatch;
	__u64 addr;        /* legal pio/mmio address */
	__u32 len;         /* 1, 2, 4, or 8 bytes    */
	__s32 fd;
	__u32 flags;
	__u8  pad[36];
};

The following flags are defined:

#define KVM_IOEVENTFD_FLAG_DATAMATCH (1 << kvm_ioeventfd_flag_nr_datamatch)
#define KVM_IOEVENTFD_FLAG_PIO       (1 << kvm_ioeventfd_flag_nr_pio)
#define KVM_IOEVENTFD_FLAG_DEASSIGN  (1 << kvm_ioeventfd_flag_nr_deassign)

If datamatch flag is set, the event will be signaled only if the written value
to the registered address is equal to datamatch in struct kvm_ioeventfd.

4.62 KVM_CREATE_SPAPR_TCE

Capability: KVM_CAP_SPAPR_TCE
Architectures: powerpc
Type: vm ioctl
Parameters: struct kvm_create_spapr_tce (in)
Returns: file descriptor for manipulating the created TCE table

This creates a virtual TCE (translation control entry) table, which
is an IOMMU for PAPR-style virtual I/O.  It is used to translate
logical addresses used in virtual I/O into guest physical addresses,
and provides a scatter/gather capability for PAPR virtual I/O.

/* for KVM_CAP_SPAPR_TCE */
struct kvm_create_spapr_tce {
	__u64 liobn;
	__u32 window_size;
};

The liobn field gives the logical IO bus number for which to create a
TCE table.  The window_size field specifies the size of the DMA window
which this TCE table will translate - the table will contain one 64
bit TCE entry for every 4kiB of the DMA window.

When the guest issues an H_PUT_TCE hcall on a liobn for which a TCE
table has been created using this ioctl(), the kernel will handle it
in real mode, updating the TCE table.  H_PUT_TCE calls for other
liobns will cause a vm exit and must be handled by userspace.

The return value is a file descriptor which can be passed to mmap(2)
to map the created TCE table into userspace.  This lets userspace read
the entries written by kernel-handled H_PUT_TCE calls, and also lets
userspace update the TCE table directly which is useful in some
circumstances.

5. The kvm_run structure

Application code obtains a pointer to the kvm_run structure by
mmap()ing a vcpu fd.  From that point, application code can control
execution by changing fields in kvm_run prior to calling the KVM_RUN
ioctl, and obtain information about the reason KVM_RUN returned by
looking up structure members.

struct kvm_run {
	/* in */
	__u8 request_interrupt_window;

Request that KVM_RUN return when it becomes possible to inject external
interrupts into the guest.  Useful in conjunction with KVM_INTERRUPT.

	__u8 padding1[7];

	/* out */
	__u32 exit_reason;

When KVM_RUN has returned successfully (return value 0), this informs
application code why KVM_RUN has returned.  Allowable values for this
field are detailed below.

	__u8 ready_for_interrupt_injection;

If request_interrupt_window has been specified, this field indicates
an interrupt can be injected now with KVM_INTERRUPT.

	__u8 if_flag;

The value of the current interrupt flag.  Only valid if in-kernel
local APIC is not used.

	__u8 padding2[2];

	/* in (pre_kvm_run), out (post_kvm_run) */
	__u64 cr8;

The value of the cr8 register.  Only valid if in-kernel local APIC is
not used.  Both input and output.

	__u64 apic_base;

The value of the APIC BASE msr.  Only valid if in-kernel local
APIC is not used.  Both input and output.

	union {
		/* KVM_EXIT_UNKNOWN */
		struct {
			__u64 hardware_exit_reason;
		} hw;

If exit_reason is KVM_EXIT_UNKNOWN, the vcpu has exited due to unknown
reasons.  Further architecture-specific information is available in
hardware_exit_reason.

		/* KVM_EXIT_FAIL_ENTRY */
		struct {
			__u64 hardware_entry_failure_reason;
		} fail_entry;

If exit_reason is KVM_EXIT_FAIL_ENTRY, the vcpu could not be run due
to unknown reasons.  Further architecture-specific information is
available in hardware_entry_failure_reason.

		/* KVM_EXIT_EXCEPTION */
		struct {
			__u32 exception;
			__u32 error_code;
		} ex;

Unused.

		/* KVM_EXIT_IO */
		struct {
#define KVM_EXIT_IO_IN  0
#define KVM_EXIT_IO_OUT 1
			__u8 direction;
			__u8 size; /* bytes */
			__u16 port;
			__u32 count;
			__u64 data_offset; /* relative to kvm_run start */
		} io;

If exit_reason is KVM_EXIT_IO, then the vcpu has
executed a port I/O instruction which could not be satisfied by kvm.
data_offset describes where the data is located (KVM_EXIT_IO_OUT) or
where kvm expects application code to place the data for the next
KVM_RUN invocation (KVM_EXIT_IO_IN).  Data format is a packed array.

		struct {
			struct kvm_debug_exit_arch arch;
		} debug;

Unused.

		/* KVM_EXIT_MMIO */
		struct {
			__u64 phys_addr;
			__u8  data[8];
			__u32 len;
			__u8  is_write;
		} mmio;

If exit_reason is KVM_EXIT_MMIO, then the vcpu has
executed a memory-mapped I/O instruction which could not be satisfied
by kvm.  The 'data' member contains the written data if 'is_write' is
true, and should be filled by application code otherwise.

NOTE: For KVM_EXIT_IO, KVM_EXIT_MMIO and KVM_EXIT_OSI, the corresponding
operations are complete (and guest state is consistent) only after userspace
has re-entered the kernel with KVM_RUN.  The kernel side will first finish
incomplete operations and then check for pending signals.  Userspace
can re-enter the guest with an unmasked signal pending to complete
pending operations.

		/* KVM_EXIT_HYPERCALL */
		struct {
			__u64 nr;
			__u64 args[6];
			__u64 ret;
			__u32 longmode;
			__u32 pad;
		} hypercall;

Unused.  This was once used for 'hypercall to userspace'.  To implement
such functionality, use KVM_EXIT_IO (x86) or KVM_EXIT_MMIO (all except s390).
Note KVM_EXIT_IO is significantly faster than KVM_EXIT_MMIO.

		/* KVM_EXIT_TPR_ACCESS */
		struct {
			__u64 rip;
			__u32 is_write;
			__u32 pad;
		} tpr_access;

To be documented (KVM_TPR_ACCESS_REPORTING).

		/* KVM_EXIT_S390_SIEIC */
		struct {
			__u8 icptcode;
			__u64 mask; /* psw upper half */
			__u64 addr; /* psw lower half */
			__u16 ipa;
			__u32 ipb;
		} s390_sieic;

s390 specific.

		/* KVM_EXIT_S390_RESET */
#define KVM_S390_RESET_POR       1
#define KVM_S390_RESET_CLEAR     2
#define KVM_S390_RESET_SUBSYSTEM 4
#define KVM_S390_RESET_CPU_INIT  8
#define KVM_S390_RESET_IPL       16
		__u64 s390_reset_flags;

s390 specific.

		/* KVM_EXIT_DCR */
		struct {
			__u32 dcrn;
			__u32 data;
			__u8  is_write;
		} dcr;

powerpc specific.

		/* KVM_EXIT_OSI */
		struct {
			__u64 gprs[32];
		} osi;

MOL uses a special hypercall interface it calls 'OSI'. To enable it, we catch
hypercalls and exit with this exit struct that contains all the guest gprs.

If exit_reason is KVM_EXIT_OSI, then the vcpu has triggered such a hypercall.
Userspace can now handle the hypercall and when it's done modify the gprs as
necessary. Upon guest entry all guest GPRs will then be replaced by the values
in this struct.

		/* KVM_EXIT_PAPR_HCALL */
		struct {
			__u64 nr;
			__u64 ret;
			__u64 args[9];
		} papr_hcall;

This is used on 64-bit PowerPC when emulating a pSeries partition,
e.g. with the 'pseries' machine type in qemu.  It occurs when the
guest does a hypercall using the 'sc 1' instruction.  The 'nr' field
contains the hypercall number (from the guest R3), and 'args' contains
the arguments (from the guest R4 - R12).  Userspace should put the
return code in 'ret' and any extra returned values in args[].
The possible hypercalls are defined in the Power Architecture Platform
Requirements (PAPR) document available from www.power.org (free
developer registration required to access it).

		/* Fix the size of the union. */
		char padding[256];
	};
};