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KVM: Document basic API
Document the basic API corresponding to the 2.6.22 release. Signed-off-by: Avi Kivity <avi@redhat.com>
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Documentation/kvm/api.txt
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Documentation/kvm/api.txt
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The Definitive KVM (Kernel-based Virtual Machine) API Documentation
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===================================================================
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1. General description
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The kvm API is a set of ioctls that are issued to control various aspects
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of a virtual machine. The ioctls belong to three classes
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- System ioctls: These query and set global attributes which affect the
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whole kvm subsystem. In addition a system ioctl is used to create
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virtual machines
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- VM ioctls: These query and set attributes that affect an entire virtual
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machine, for example memory layout. In addition a VM ioctl is used to
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create virtual cpus (vcpus).
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Only run VM ioctls from the same process (address space) that was used
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to create the VM.
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- vcpu ioctls: These query and set attributes that control the operation
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of a single virtual cpu.
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Only run vcpu ioctls from the same thread that was used to create the
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vcpu.
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2. File descritpors
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The kvm API is centered around file descriptors. An initial
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open("/dev/kvm") obtains a handle to the kvm subsystem; this handle
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can be used to issue system ioctls. A KVM_CREATE_VM ioctl on this
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handle will create a VM file descripror which can be used to issue VM
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ioctls. A KVM_CREATE_VCPU ioctl on a VM fd will create a virtual cpu
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and return a file descriptor pointing to it. Finally, ioctls on a vcpu
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fd can be used to control the vcpu, including the important task of
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actually running guest code.
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In general file descriptors can be migrated among processes by means
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of fork() and the SCM_RIGHTS facility of unix domain socket. These
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kinds of tricks are explicitly not supported by kvm. While they will
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not cause harm to the host, their actual behavior is not guaranteed by
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the API. The only supported use is one virtual machine per process,
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and one vcpu per thread.
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3. Extensions
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As of Linux 2.6.22, the KVM ABI has been stabilized: no backward
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incompatible change are allowed. However, there is an extension
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facility that allows backward-compatible extensions to the API to be
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queried and used.
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The extension mechanism is not based on on the Linux version number.
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Instead, kvm defines extension identifiers and a facility to query
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whether a particular extension identifier is available. If it is, a
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set of ioctls is available for application use.
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4. API description
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This section describes ioctls that can be used to control kvm guests.
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For each ioctl, the following information is provided along with a
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description:
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Capability: which KVM extension provides this ioctl. Can be 'basic',
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which means that is will be provided by any kernel that supports
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API version 12 (see section 4.1), or a KVM_CAP_xyz constant, which
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means availability needs to be checked with KVM_CHECK_EXTENSION
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(see section 4.4).
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Architectures: which instruction set architectures provide this ioctl.
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x86 includes both i386 and x86_64.
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Type: system, vm, or vcpu.
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Parameters: what parameters are accepted by the ioctl.
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Returns: the return value. General error numbers (EBADF, ENOMEM, EINVAL)
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are not detailed, but errors with specific meanings are.
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4.1 KVM_GET_API_VERSION
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Capability: basic
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Architectures: all
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Type: system ioctl
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Parameters: none
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Returns: the constant KVM_API_VERSION (=12)
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This identifies the API version as the stable kvm API. It is not
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expected that this number will change. However, Linux 2.6.20 and
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2.6.21 report earlier versions; these are not documented and not
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supported. Applications should refuse to run if KVM_GET_API_VERSION
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returns a value other than 12. If this check passes, all ioctls
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described as 'basic' will be available.
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4.2 KVM_CREATE_VM
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Capability: basic
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Architectures: all
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Type: system ioctl
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Parameters: none
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Returns: a VM fd that can be used to control the new virtual machine.
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The new VM has no virtual cpus and no memory. An mmap() of a VM fd
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will access the virtual machine's physical address space; offset zero
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corresponds to guest physical address zero. Use of mmap() on a VM fd
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is discouraged if userspace memory allocation (KVM_CAP_USER_MEMORY) is
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available.
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4.3 KVM_GET_MSR_INDEX_LIST
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Capability: basic
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Architectures: x86
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Type: system
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Parameters: struct kvm_msr_list (in/out)
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Returns: 0 on success; -1 on error
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Errors:
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E2BIG: the msr index list is to be to fit in the array specified by
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the user.
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struct kvm_msr_list {
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__u32 nmsrs; /* number of msrs in entries */
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__u32 indices[0];
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};
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This ioctl returns the guest msrs that are supported. The list varies
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by kvm version and host processor, but does not change otherwise. The
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user fills in the size of the indices array in nmsrs, and in return
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kvm adjusts nmsrs to reflect the actual number of msrs and fills in
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the indices array with their numbers.
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4.4 KVM_CHECK_EXTENSION
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Capability: basic
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Architectures: all
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Type: system ioctl
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Parameters: extension identifier (KVM_CAP_*)
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Returns: 0 if unsupported; 1 (or some other positive integer) if supported
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The API allows the application to query about extensions to the core
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kvm API. Userspace passes an extension identifier (an integer) and
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receives an integer that describes the extension availability.
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Generally 0 means no and 1 means yes, but some extensions may report
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additional information in the integer return value.
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4.5 KVM_GET_VCPU_MMAP_SIZE
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Capability: basic
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Architectures: all
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Type: system ioctl
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Parameters: none
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Returns: size of vcpu mmap area, in bytes
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The KVM_RUN ioctl (cf.) communicates with userspace via a shared
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memory region. This ioctl returns the size of that region. See the
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KVM_RUN documentation for details.
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4.6 KVM_SET_MEMORY_REGION
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Capability: basic
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Architectures: all
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Type: vm ioctl
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Parameters: struct kvm_memory_region (in)
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Returns: 0 on success, -1 on error
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struct kvm_memory_region {
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__u32 slot;
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__u32 flags;
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__u64 guest_phys_addr;
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__u64 memory_size; /* bytes */
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};
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/* for kvm_memory_region::flags */
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#define KVM_MEM_LOG_DIRTY_PAGES 1UL
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This ioctl allows the user to create or modify a guest physical memory
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slot. When changing an existing slot, it may be moved in the guest
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physical memory space, or its flags may be modified. It may not be
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resized. Slots may not overlap.
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The flags field supports just one flag, KVM_MEM_LOG_DIRTY_PAGES, which
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instructs kvm to keep track of writes to memory within the slot. See
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the KVM_GET_DIRTY_LOG ioctl.
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It is recommended to use the KVM_SET_USER_MEMORY_REGION ioctl instead
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of this API, if available. This newer API allows placing guest memory
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at specified locations in the host address space, yielding better
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control and easy access.
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4.6 KVM_CREATE_VCPU
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Capability: basic
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Architectures: all
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Type: vm ioctl
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Parameters: vcpu id (apic id on x86)
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Returns: vcpu fd on success, -1 on error
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This API adds a vcpu to a virtual machine. The vcpu id is a small integer
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in the range [0, max_vcpus).
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4.7 KVM_GET_DIRTY_LOG (vm ioctl)
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Capability: basic
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Architectures: x86
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Type: vm ioctl
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Parameters: struct kvm_dirty_log (in/out)
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Returns: 0 on success, -1 on error
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/* for KVM_GET_DIRTY_LOG */
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struct kvm_dirty_log {
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__u32 slot;
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__u32 padding;
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union {
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void __user *dirty_bitmap; /* one bit per page */
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__u64 padding;
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};
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};
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Given a memory slot, return a bitmap containing any pages dirtied
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since the last call to this ioctl. Bit 0 is the first page in the
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memory slot. Ensure the entire structure is cleared to avoid padding
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issues.
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4.8 KVM_SET_MEMORY_ALIAS
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Capability: basic
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Architectures: x86
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Type: vm ioctl
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Parameters: struct kvm_memory_alias (in)
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Returns: 0 (success), -1 (error)
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struct kvm_memory_alias {
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__u32 slot; /* this has a different namespace than memory slots */
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__u32 flags;
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__u64 guest_phys_addr;
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__u64 memory_size;
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__u64 target_phys_addr;
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};
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Defines a guest physical address space region as an alias to another
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region. Useful for aliased address, for example the VGA low memory
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window. Should not be used with userspace memory.
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4.9 KVM_RUN
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Capability: basic
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Architectures: all
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Type: vcpu ioctl
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Parameters: none
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Returns: 0 on success, -1 on error
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Errors:
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EINTR: an unmasked signal is pending
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This ioctl is used to run a guest virtual cpu. While there are no
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explicit parameters, there is an implicit parameter block that can be
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obtained by mmap()ing the vcpu fd at offset 0, with the size given by
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KVM_GET_VCPU_MMAP_SIZE. The parameter block is formatted as a 'struct
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kvm_run' (see below).
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4.10 KVM_GET_REGS
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Capability: basic
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Architectures: all
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Type: vcpu ioctl
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Parameters: struct kvm_regs (out)
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Returns: 0 on success, -1 on error
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Reads the general purpose registers from the vcpu.
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/* x86 */
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struct kvm_regs {
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/* out (KVM_GET_REGS) / in (KVM_SET_REGS) */
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__u64 rax, rbx, rcx, rdx;
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__u64 rsi, rdi, rsp, rbp;
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__u64 r8, r9, r10, r11;
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__u64 r12, r13, r14, r15;
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__u64 rip, rflags;
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};
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4.11 KVM_SET_REGS
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Capability: basic
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Architectures: all
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Type: vcpu ioctl
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Parameters: struct kvm_regs (in)
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Returns: 0 on success, -1 on error
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Writes the general purpose registers into the vcpu.
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See KVM_GET_REGS for the data structure.
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4.12 KVM_GET_SREGS
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Capability: basic
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Architectures: x86
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Type: vcpu ioctl
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Parameters: struct kvm_sregs (out)
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Returns: 0 on success, -1 on error
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Reads special registers from the vcpu.
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/* x86 */
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struct kvm_sregs {
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struct kvm_segment cs, ds, es, fs, gs, ss;
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struct kvm_segment tr, ldt;
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struct kvm_dtable gdt, idt;
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__u64 cr0, cr2, cr3, cr4, cr8;
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__u64 efer;
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__u64 apic_base;
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__u64 interrupt_bitmap[(KVM_NR_INTERRUPTS + 63) / 64];
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};
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interrupt_bitmap is a bitmap of pending external interrupts. At most
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one bit may be set. This interrupt has been acknowledged by the APIC
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but not yet injected into the cpu core.
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4.13 KVM_SET_SREGS
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Capability: basic
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Architectures: x86
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Type: vcpu ioctl
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Parameters: struct kvm_sregs (in)
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Returns: 0 on success, -1 on error
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Writes special registers into the vcpu. See KVM_GET_SREGS for the
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data structures.
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4.14 KVM_TRANSLATE
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Capability: basic
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Architectures: x86
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Type: vcpu ioctl
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Parameters: struct kvm_translation (in/out)
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Returns: 0 on success, -1 on error
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Translates a virtual address according to the vcpu's current address
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translation mode.
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struct kvm_translation {
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/* in */
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__u64 linear_address;
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/* out */
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__u64 physical_address;
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__u8 valid;
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__u8 writeable;
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__u8 usermode;
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__u8 pad[5];
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};
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4.15 KVM_INTERRUPT
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Capability: basic
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Architectures: x86
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Type: vcpu ioctl
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Parameters: struct kvm_interrupt (in)
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Returns: 0 on success, -1 on error
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Queues a hardware interrupt vector to be injected. This is only
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useful if in-kernel local APIC is not used.
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/* for KVM_INTERRUPT */
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struct kvm_interrupt {
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/* in */
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__u32 irq;
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};
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Note 'irq' is an interrupt vector, not an interrupt pin or line.
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4.16 KVM_DEBUG_GUEST
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Capability: basic
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Architectures: none
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Type: vcpu ioctl
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Parameters: none)
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Returns: -1 on error
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Support for this has been removed. Use KVM_SET_GUEST_DEBUG instead.
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4.17 KVM_GET_MSRS
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Capability: basic
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Architectures: x86
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Type: vcpu ioctl
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Parameters: struct kvm_msrs (in/out)
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Returns: 0 on success, -1 on error
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Reads model-specific registers from the vcpu. Supported msr indices can
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be obtained using KVM_GET_MSR_INDEX_LIST.
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struct kvm_msrs {
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__u32 nmsrs; /* number of msrs in entries */
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__u32 pad;
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struct kvm_msr_entry entries[0];
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};
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struct kvm_msr_entry {
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__u32 index;
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__u32 reserved;
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__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.
|
||||||
|
|
||||||
|
4.18 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.
|
||||||
|
|
||||||
|
4.19 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];
|
||||||
|
};
|
||||||
|
|
||||||
|
4.20 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];
|
||||||
|
};
|
||||||
|
|
||||||
|
4.21 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;
|
||||||
|
};
|
||||||
|
|
||||||
|
4.22 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;
|
||||||
|
};
|
||||||
|
|
||||||
|
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_IN or KVM_EXIT_IO_OUT, 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 patcked 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 or KVM_EXIT_IO_OUT, 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.
|
||||||
|
|
||||||
|
/* KVM_EXIT_HYPERCALL */
|
||||||
|
struct {
|
||||||
|
__u64 nr;
|
||||||
|
__u64 args[6];
|
||||||
|
__u64 ret;
|
||||||
|
__u32 longmode;
|
||||||
|
__u32 pad;
|
||||||
|
} hypercall;
|
||||||
|
|
||||||
|
Unused.
|
||||||
|
|
||||||
|
/* 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.
|
||||||
|
|
||||||
|
/* Fix the size of the union. */
|
||||||
|
char padding[256];
|
||||||
|
};
|
||||||
|
};
|
||||||
Loading…
Reference in a new issue