api.txt

The "sps" array contains 8 entries indicating the supported base
page sizes for a segment in increasing order. Each entry is defined
as follow:

   struct kvm_ppc_one_seg_page_size {
	__u32 page_shift;	/* Base page shift of segment (or 0) */
	__u32 slb_enc;		/* SLB encoding for BookS */
	struct kvm_ppc_one_page_size enc[KVM_PPC_PAGE_SIZES_MAX_SZ];
   };

An entry with a "page_shift" of 0 is unused. Because the array is
organized in increasing order, a lookup can stop when encoutering
such an entry.

The "slb_enc" field provides the encoding to use in the SLB for the
page size. The bits are in positions such as the value can directly
be OR'ed into the "vsid" argument of the slbmte instruction.

The "enc" array is a list which for each of those segment base page
size provides the list of supported actual page sizes (which can be
only larger or equal to the base page size), along with the
corresponding encoding in the hash PTE. Similarly, the array is
8 entries sorted by increasing sizes and an entry with a "0" shift
is an empty entry and a terminator:

   struct kvm_ppc_one_page_size {
	__u32 page_shift;	/* Page shift (or 0) */
	__u32 pte_enc;		/* Encoding in the HPTE (>>12) */
   };

The "pte_enc" field provides a value that can OR'ed into the hash
PTE's RPN field (ie, it needs to be shifted left by 12 to OR it
into the hash PTE second double word).

4.75 KVM_IRQFD

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

Allows setting an eventfd to directly trigger a guest interrupt.
kvm_irqfd.fd specifies the file descriptor to use as the eventfd and
kvm_irqfd.gsi specifies the irqchip pin toggled by this event.  When
an event is tiggered on the eventfd, an interrupt is injected into
the guest using the specified gsi pin.  The irqfd is removed using
the KVM_IRQFD_FLAG_DEASSIGN flag, specifying both kvm_irqfd.fd
and kvm_irqfd.gsi.

With KVM_CAP_IRQFD_RESAMPLE, KVM_IRQFD supports a de-assert and notify
mechanism allowing emulation of level-triggered, irqfd-based
interrupts.  When KVM_IRQFD_FLAG_RESAMPLE is set the user must pass an
additional eventfd in the kvm_irqfd.resamplefd field.  When operating
in resample mode, posting of an interrupt through kvm_irq.fd asserts
the specified gsi in the irqchip.  When the irqchip is resampled, such
as from an EOI, the gsi is de-asserted and the user is notifed via
kvm_irqfd.resamplefd.  It is the user's responsibility to re-queue
the interrupt if the device making use of it still requires service.
Note that closing the resamplefd is not sufficient to disable the
irqfd.  The KVM_IRQFD_FLAG_RESAMPLE is only necessary on assignment
and need not be specified with KVM_IRQFD_FLAG_DEASSIGN.

4.76 KVM_PPC_ALLOCATE_HTAB

Capability: KVM_CAP_PPC_ALLOC_HTAB
Architectures: powerpc
Type: vm ioctl
Parameters: Pointer to u32 containing hash table order (in/out)
Returns: 0 on success, -1 on error

This requests the host kernel to allocate an MMU hash table for a
guest using the PAPR paravirtualization interface.  This only does
anything if the kernel is configured to use the Book 3S HV style of
virtualization.  Otherwise the capability doesn't exist and the ioctl
returns an ENOTTY error.  The rest of this description assumes Book 3S
HV.

There must be no vcpus running when this ioctl is called; if there
are, it will do nothing and return an EBUSY error.

The parameter is a pointer to a 32-bit unsigned integer variable
containing the order (log base 2) of the desired size of the hash
table, which must be between 18 and 46.  On successful return from the
ioctl, it will have been updated with the order of the hash table that
was allocated.

If no hash table has been allocated when any vcpu is asked to run
(with the KVM_RUN ioctl), the host kernel will allocate a
default-sized hash table (16 MB).

If this ioctl is called when a hash table has already been allocated,
the kernel will clear out the existing hash table (zero all HPTEs) and
return the hash table order in the parameter.  (If the guest is using
the virtualized real-mode area (VRMA) facility, the kernel will
re-create the VMRA HPTEs on the next KVM_RUN of any vcpu.)

4.77 KVM_S390_INTERRUPT

Capability: basic
Architectures: s390
Type: vm ioctl, vcpu ioctl
Parameters: struct kvm_s390_interrupt (in)
Returns: 0 on success, -1 on error

Allows to inject an interrupt to the guest. Interrupts can be floating
(vm ioctl) or per cpu (vcpu ioctl), depending on the interrupt type.

Interrupt parameters are passed via kvm_s390_interrupt:

struct kvm_s390_interrupt {
	__u32 type;
	__u32 parm;
	__u64 parm64;
};

type can be one of the following:

KVM_S390_SIGP_STOP (vcpu) - sigp restart
KVM_S390_PROGRAM_INT (vcpu) - program check; code in parm
KVM_S390_SIGP_SET_PREFIX (vcpu) - sigp set prefix; prefix address in parm
KVM_S390_RESTART (vcpu) - restart
KVM_S390_INT_VIRTIO (vm) - virtio external interrupt; external interrupt
			   parameters in parm and parm64
KVM_S390_INT_SERVICE (vm) - sclp external interrupt; sclp parameter in parm
KVM_S390_INT_EMERGENCY (vcpu) - sigp emergency; source cpu in parm
KVM_S390_INT_EXTERNAL_CALL (vcpu) - sigp external call; source cpu in parm
KVM_S390_INT_IO(ai,cssid,ssid,schid) (vm) - compound value to indicate an
    I/O interrupt (ai - adapter interrupt; cssid,ssid,schid - subchannel);
    I/O interruption parameters in parm (subchannel) and parm64 (intparm,
    interruption subclass)
KVM_S390_MCHK (vm, vcpu) - machine check interrupt; cr 14 bits in parm,
                           machine check interrupt code in parm64 (note that
                           machine checks needing further payload are not
                           supported by this ioctl)

Note that the vcpu ioctl is asynchronous to vcpu execution.

4.78 KVM_PPC_GET_HTAB_FD

Capability: KVM_CAP_PPC_HTAB_FD
Architectures: powerpc
Type: vm ioctl
Parameters: Pointer to struct kvm_get_htab_fd (in)
Returns: file descriptor number (>= 0) on success, -1 on error

This returns a file descriptor that can be used either to read out the
entries in the guest's hashed page table (HPT), or to write entries to
initialize the HPT.  The returned fd can only be written to if the
KVM_GET_HTAB_WRITE bit is set in the flags field of the argument, and
can only be read if that bit is clear.  The argument struct looks like
this:

/* For KVM_PPC_GET_HTAB_FD */
struct kvm_get_htab_fd {
	__u64	flags;
	__u64	start_index;
	__u64	reserved[2];
};

/* Values for kvm_get_htab_fd.flags */
#define KVM_GET_HTAB_BOLTED_ONLY	((__u64)0x1)
#define KVM_GET_HTAB_WRITE		((__u64)0x2)

The `start_index' field gives the index in the HPT of the entry at
which to start reading.  It is ignored when writing.

Reads on the fd will initially supply information about all
"interesting" HPT entries.  Interesting entries are those with the
bolted bit set, if the KVM_GET_HTAB_BOLTED_ONLY bit is set, otherwise
all entries.  When the end of the HPT is reached, the read() will
return.  If read() is called again on the fd, it will start again from
the beginning of the HPT, but will only return HPT entries that have
changed since they were last read.

Data read or written is structured as a header (8 bytes) followed by a
series of valid HPT entries (16 bytes) each.  The header indicates how
many valid HPT entries there are and how many invalid entries follow
the valid entries.  The invalid entries are not represented explicitly
in the stream.  The header format is:

struct kvm_get_htab_header {
	__u32	index;
	__u16	n_valid;
	__u16	n_invalid;
};

Writes to the fd create HPT entries starting at the index given in the
header; first `n_valid' valid entries with contents from the data
written, then `n_invalid' invalid entries, invalidating any previously
valid entries found.

4.79 KVM_CREATE_DEVICE

Capability: KVM_CAP_DEVICE_CTRL
Type: vm ioctl
Parameters: struct kvm_create_device (in/out)
Returns: 0 on success, -1 on error
Errors:
  ENODEV: The device type is unknown or unsupported
  EEXIST: Device already created, and this type of device may not
          be instantiated multiple times

  Other error conditions may be defined by individual device types or
  have their standard meanings.

Creates an emulated device in the kernel.  The file descriptor returned
in fd can be used with KVM_SET/GET/HAS_DEVICE_ATTR.

If the KVM_CREATE_DEVICE_TEST flag is set, only test whether the
device type is supported (not necessarily whether it can be created
in the current vm).

Individual devices should not define flags.  Attributes should be used
for specifying any behavior that is not implied by the device type
number.

struct kvm_create_device {
	__u32	type;	/* in: KVM_DEV_TYPE_xxx */
	__u32	fd;	/* out: device handle */
	__u32	flags;	/* in: KVM_CREATE_DEVICE_xxx */
};

4.80 KVM_SET_DEVICE_ATTR/KVM_GET_DEVICE_ATTR

Capability: KVM_CAP_DEVICE_CTRL
Type: device ioctl
Parameters: struct kvm_device_attr
Returns: 0 on success, -1 on error
Errors:
  ENXIO:  The group or attribute is unknown/unsupported for this device
  EPERM:  The attribute cannot (currently) be accessed this way
          (e.g. read-only attribute, or attribute that only makes
          sense when the device is in a different state)

  Other error conditions may be defined by individual device types.

Gets/sets a specified piece of device configuration and/or state.  The
semantics are device-specific.  See individual device documentation in
the "devices" directory.  As with ONE_REG, the size of the data
transferred is defined by the particular attribute.

struct kvm_device_attr {
	__u32	flags;		/* no flags currently defined */
	__u32	group;		/* device-defined */
	__u64	attr;		/* group-defined */
	__u64	addr;		/* userspace address of attr data */
};

4.81 KVM_HAS_DEVICE_ATTR

Capability: KVM_CAP_DEVICE_CTRL
Type: device ioctl
Parameters: struct kvm_device_attr
Returns: 0 on success, -1 on error
Errors:
  ENXIO:  The group or attribute is unknown/unsupported for this device

Tests whether a device supports a particular attribute.  A successful
return indicates the attribute is implemented.  It does not necessarily
indicate that the attribute can be read or written in the device's
current state.  "addr" is ignored.

4.77 KVM_ARM_VCPU_INIT

Capability: basic
Architectures: arm
Type: vcpu ioctl
Parameters: struct struct kvm_vcpu_init (in)
Returns: 0 on success; -1 on error
Errors:
  EINVAL:    the target is unknown, or the combination of features is invalid.
  ENOENT:    a features bit specified is unknown.

This tells KVM what type of CPU to present to the guest, and what
optional features it should have.  This will cause a reset of the cpu
registers to their initial values.  If this is not called, KVM_RUN will
return ENOEXEC for that vcpu.

Note that because some registers reflect machine topology, all vcpus
should be created before this ioctl is invoked.

Possible features:
	- KVM_ARM_VCPU_POWER_OFF: Starts the CPU in a power-off state.
	  Depends on KVM_CAP_ARM_PSCI.


4.78 KVM_GET_REG_LIST

Capability: basic
Architectures: arm
Type: vcpu ioctl
Parameters: struct kvm_reg_list (in/out)
Returns: 0 on success; -1 on error
Errors:
  E2BIG:     the reg index list is too big to fit in the array specified by
             the user (the number required will be written into n).

struct kvm_reg_list {
	__u64 n; /* number of registers in reg[] */
	__u64 reg[0];
};

This ioctl returns the guest registers that are supported for the
KVM_GET_ONE_REG/KVM_SET_ONE_REG calls.


4.80 KVM_ARM_SET_DEVICE_ADDR

Capability: KVM_CAP_ARM_SET_DEVICE_ADDR
Architectures: arm
Type: vm ioctl
Parameters: struct kvm_arm_device_address (in)
Returns: 0 on success, -1 on error
Errors:
  ENODEV: The device id is unknown
  ENXIO:  Device not supported on current system
  EEXIST: Address already set
  E2BIG:  Address outside guest physical address space
  EBUSY:  Address overlaps with other device range

struct kvm_arm_device_addr {
	__u64 id;
	__u64 addr;
};

Specify a device address in the guest's physical address space where guests
can access emulated or directly exposed devices, which the host kernel needs
to know about. The id field is an architecture specific identifier for a
specific device.

ARM divides the id field into two parts, a device id and an address type id
specific to the individual device.

  bits:  | 63        ...       32 | 31    ...    16 | 15    ...    0 |
  field: |        0x00000000      |     device id   |  addr type id  |

ARM currently only require this when using the in-kernel GIC support for the
hardware VGIC features, using KVM_ARM_DEVICE_VGIC_V2 as the device id.  When
setting the base address for the guest's mapping of the VGIC virtual CPU
and distributor interface, the ioctl must be called after calling
KVM_CREATE_IRQCHIP, but before calling KVM_RUN on any of the VCPUs.  Calling
this ioctl twice for any of the base addresses will return -EEXIST.

4.82 KVM_PPC_RTAS_DEFINE_TOKEN

Capability: KVM_CAP_PPC_RTAS
Architectures: ppc
Type: vm ioctl
Parameters: struct kvm_rtas_token_args
Returns: 0 on success, -1 on error

Defines a token value for a RTAS (Run Time Abstraction Services)
service in order to allow it to be handled in the kernel.  The
argument struct gives the name of the service, which must be the name
of a service that has a kernel-side implementation.  If the token
value is non-zero, it will be associated with that service, and
subsequent RTAS calls by the guest specifying that token will be
handled by the kernel.  If the token value is 0, then any token
associated with the service will be forgotten, and subsequent RTAS
calls by the guest for that service will be passed to userspace to be
handled.


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, KVM_EXIT_OSI, KVM_EXIT_DCR,
      KVM_EXIT_PAPR and KVM_EXIT_EPR 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_S390_UCONTROL */
		struct {
			__u64 trans_exc_code;
			__u32 pgm_code;
		} s390_ucontrol;

s390 specific. A page fault has occurred for a user controlled virtual
machine (KVM_VM_S390_UNCONTROL) on it's host page table that cannot be
resolved by the kernel.
The program code and the translation exception code that were placed
in the cpu's lowcore are presented here as defined by the z Architecture
Principles of Operation Book in the Chapter for Dynamic Address Translation
(DAT)

		/* 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).

		/* KVM_EXIT_S390_TSCH */
		struct {
			__u16 subchannel_id;
			__u16 subchannel_nr;
			__u32 io_int_parm;
			__u32 io_int_word;
			__u32 ipb;
			__u8 dequeued;
		} s390_tsch;

s390 specific. This exit occurs when KVM_CAP_S390_CSS_SUPPORT has been enabled
and TEST SUBCHANNEL was intercepted. If dequeued is set, a pending I/O
interrupt for the target subchannel has been dequeued and subchannel_id,
subchannel_nr, io_int_parm and io_int_word contain the parameters for that
interrupt. ipb is needed for instruction parameter decoding.

		/* KVM_EXIT_EPR */
		struct {
			__u32 epr;
		} epr;

On FSL BookE PowerPC chips, the interrupt controller has a fast patch
interrupt acknowledge path to the core. When the core successfully
delivers an interrupt, it automatically populates the EPR register with
the interrupt vector number and acknowledges the interrupt inside
the interrupt controller.

In case the interrupt controller lives in user space, we need to do
the interrupt acknowledge cycle through it to fetch the next to be
delivered interrupt vector using this exit.

It gets triggered whenever both KVM_CAP_PPC_EPR are enabled and an
external interrupt has just been delivered into the guest. User space
should put the acknowledged interrupt vector into the 'epr' field.

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

	/*
	 * shared registers between kvm and userspace.
	 * kvm_valid_regs specifies the register classes set by the host
	 * kvm_dirty_regs specified the register classes dirtied by userspace
	 * struct kvm_sync_regs is architecture specific, as well as the
	 * bits for kvm_valid_regs and kvm_dirty_regs
	 */
	__u64 kvm_valid_regs;
	__u64 kvm_dirty_regs;
	union {
		struct kvm_sync_regs regs;
		char padding[1024];
	} s;

If KVM_CAP_SYNC_REGS is defined, these fields allow userspace to access
certain guest registers without having to call SET/GET_*REGS. Thus we can
avoid some system call overhead if userspace has to handle the exit.
Userspace can query the validity of the structure by checking
kvm_valid_regs for specific bits. These bits are architecture specific
and usually define the validity of a groups of registers. (e.g. one bit
 for general purpose registers)

};


6. Capabilities that can be enabled
-----------------------------------

There are certain capabilities that change the behavior of the virtual CPU when
enabled. To enable them, please see section 4.37. Below you can find a list of
capabilities and what their effect on the vCPU is when enabling them.

The following information is provided along with the description:

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

  Parameters: what parameters are accepted by the capability.

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


6.1 KVM_CAP_PPC_OSI

Architectures: ppc
Parameters: none
Returns: 0 on success; -1 on error

This capability enables interception of OSI hypercalls that otherwise would
be treated as normal system calls to be injected into the guest. OSI hypercalls
were invented by Mac-on-Linux to have a standardized communication mechanism
between the guest and the host.

When this capability is enabled, KVM_EXIT_OSI can occur.


6.2 KVM_CAP_PPC_PAPR

Architectures: ppc
Parameters: none
Returns: 0 on success; -1 on error

This capability enables interception of PAPR hypercalls. PAPR hypercalls are
done using the hypercall instruction "sc 1".

It also sets the guest privilege level to "supervisor" mode. Usually the guest
runs in "hypervisor" privilege mode with a few missing features.

In addition to the above, it changes the semantics of SDR1. In this mode, the
HTAB address part of SDR1 contains an HVA instead of a GPA, as PAPR keeps the
HTAB invisible to the guest.

When this capability is enabled, KVM_EXIT_PAPR_HCALL can occur.


6.3 KVM_CAP_SW_TLB

Architectures: ppc
Parameters: args[0] is the address of a struct kvm_config_tlb
Returns: 0 on success; -1 on error

struct kvm_config_tlb {
	__u64 params;
	__u64 array;
	__u32 mmu_type;
	__u32 array_len;
};

Configures the virtual CPU's TLB array, establishing a shared memory area
between userspace and KVM.  The "params" and "array" fields are userspace
addresses of mmu-type-specific data structures.  The "array_len" field is an
safety mechanism, and should be set to the size in bytes of the memory that
userspace has reserved for the array.  It must be at least the size dictated
by "mmu_type" and "params".

While KVM_RUN is active, the shared region is under control of KVM.  Its
contents are undefined, and any modification by userspace results in
boundedly undefined behavior.

On return from KVM_RUN, the shared region will reflect the current state of
the guest's TLB.  If userspace makes any changes, it must call KVM_DIRTY_TLB
to tell KVM which entries have been changed, prior to calling KVM_RUN again
on this vcpu.

For mmu types KVM_MMU_FSL_BOOKE_NOHV and KVM_MMU_FSL_BOOKE_HV:
 - The "params" field is of type "struct kvm_book3e_206_tlb_params".
 - The "array" field points to an array of type "struct
   kvm_book3e_206_tlb_entry".
 - The array consists of all entries in the first TLB, followed by all
   entries in the second TLB.
 - Within a TLB, entries are ordered first by increasing set number.  Within a
   set, entries are ordered by way (increasing ESEL).
 - The hash for determining set number in TLB0 is: (MAS2 >> 12) & (num_sets - 1)
   where "num_sets" is the tlb_sizes[] value divided by the tlb_ways[] value.
 - The tsize field of mas1 shall be set to 4K on TLB0, even though the
   hardware ignores this value for TLB0.

6.4 KVM_CAP_S390_CSS_SUPPORT

Architectures: s390
Parameters: none
Returns: 0 on success; -1 on error

This capability enables support for handling of channel I/O instructions.

TEST PENDING INTERRUPTION and the interrupt portion of TEST SUBCHANNEL are
handled in-kernel, while the other I/O instructions are passed to userspace.

When this capability is enabled, KVM_EXIT_S390_TSCH will occur on TEST
SUBCHANNEL intercepts.

6.5 KVM_CAP_PPC_EPR

Architectures: ppc
Parameters: args[0] defines whether the proxy facility is active
Returns: 0 on success; -1 on error

This capability enables or disables the delivery of interrupts through the
external proxy facility.

When enabled (args[0] != 0), every time the guest gets an external interrupt
delivered, it automatically exits into user space with a KVM_EXIT_EPR exit
to receive the topmost interrupt vector.

When disabled (args[0] == 0), behavior is as if this facility is unsupported.

When this capability is enabled, KVM_EXIT_EPR can occur.

6.6 KVM_CAP_IRQ_MPIC

Architectures: ppc
Parameters: args[0] is the MPIC device fd
            args[1] is the MPIC CPU number for this vcpu

This capability connects the vcpu to an in-kernel MPIC device.

6.7 KVM_CAP_IRQ_XICS

Architectures: ppc
Parameters: args[0] is the XICS device fd
            args[1] is the XICS CPU number (server ID) for this vcpu

This capability connects the vcpu to an in-kernel XICS device.