126 lines
5.5 KiB
Plaintext
126 lines
5.5 KiB
Plaintext
*** BIG FAT WARNING ***
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The kvm module is currently in EXPERIMENTAL state for s390. This means that
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the interface to the module is not yet considered to remain stable. Thus, be
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prepared that we keep breaking your userspace application and guest
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compatibility over and over again until we feel happy with the result. Make sure
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your guest kernel, your host kernel, and your userspace launcher are in a
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consistent state.
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This Documentation describes the unique ioctl calls to /dev/kvm, the resulting
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kvm-vm file descriptors, and the kvm-vcpu file descriptors that differ from x86.
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1. ioctl calls to /dev/kvm
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KVM does support the following ioctls on s390 that are common with other
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architectures and do behave the same:
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KVM_GET_API_VERSION
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KVM_CREATE_VM (*) see note
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KVM_CHECK_EXTENSION
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KVM_GET_VCPU_MMAP_SIZE
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Notes:
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* KVM_CREATE_VM may fail on s390, if the calling process has multiple
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threads and has not called KVM_S390_ENABLE_SIE before.
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In addition, on s390 the following architecture specific ioctls are supported:
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ioctl: KVM_S390_ENABLE_SIE
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args: none
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see also: include/linux/kvm.h
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This call causes the kernel to switch on PGSTE in the user page table. This
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operation is needed in order to run a virtual machine, and it requires the
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calling process to be single-threaded. Note that the first call to KVM_CREATE_VM
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will implicitly try to switch on PGSTE if the user process has not called
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KVM_S390_ENABLE_SIE before. User processes that want to launch multiple threads
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before creating a virtual machine have to call KVM_S390_ENABLE_SIE, or will
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observe an error calling KVM_CREATE_VM. Switching on PGSTE is a one-time
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operation, is not reversible, and will persist over the entire lifetime of
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the calling process. It does not have any user-visible effect other than a small
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performance penalty.
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2. ioctl calls to the kvm-vm file descriptor
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KVM does support the following ioctls on s390 that are common with other
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architectures and do behave the same:
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KVM_CREATE_VCPU
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KVM_SET_USER_MEMORY_REGION (*) see note
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KVM_GET_DIRTY_LOG (**) see note
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Notes:
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* kvm does only allow exactly one memory slot on s390, which has to start
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at guest absolute address zero and at a user address that is aligned on any
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page boundary. This hardware "limitation" allows us to have a few unique
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optimizations. The memory slot doesn't have to be filled
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with memory actually, it may contain sparse holes. That said, with different
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user memory layout this does still allow a large flexibility when
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doing the guest memory setup.
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** KVM_GET_DIRTY_LOG doesn't work properly yet. The user will receive an empty
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log. This ioctl call is only needed for guest migration, and we intend to
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implement this one in the future.
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In addition, on s390 the following architecture specific ioctls for the kvm-vm
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file descriptor are supported:
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ioctl: KVM_S390_INTERRUPT
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args: struct kvm_s390_interrupt *
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see also: include/linux/kvm.h
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This ioctl is used to submit a floating interrupt for a virtual machine.
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Floating interrupts may be delivered to any virtual cpu in the configuration.
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Only some interrupt types defined in include/linux/kvm.h make sense when
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submitted as floating interrupts. The following interrupts are not considered
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to be useful as floating interrupts, and a call to inject them will result in
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-EINVAL error code: program interrupts and interprocessor signals. Valid
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floating interrupts are:
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KVM_S390_INT_VIRTIO
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KVM_S390_INT_SERVICE
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3. ioctl calls to the kvm-vcpu file descriptor
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KVM does support the following ioctls on s390 that are common with other
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architectures and do behave the same:
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KVM_RUN
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KVM_GET_REGS
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KVM_SET_REGS
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KVM_GET_SREGS
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KVM_SET_SREGS
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KVM_GET_FPU
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KVM_SET_FPU
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In addition, on s390 the following architecture specific ioctls for the
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kvm-vcpu file descriptor are supported:
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ioctl: KVM_S390_INTERRUPT
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args: struct kvm_s390_interrupt *
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see also: include/linux/kvm.h
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This ioctl is used to submit an interrupt for a specific virtual cpu.
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Only some interrupt types defined in include/linux/kvm.h make sense when
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submitted for a specific cpu. The following interrupts are not considered
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to be useful, and a call to inject them will result in -EINVAL error code:
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service processor calls and virtio interrupts. Valid interrupt types are:
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KVM_S390_PROGRAM_INT
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KVM_S390_SIGP_STOP
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KVM_S390_RESTART
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KVM_S390_SIGP_SET_PREFIX
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KVM_S390_INT_EMERGENCY
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ioctl: KVM_S390_STORE_STATUS
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args: unsigned long
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see also: include/linux/kvm.h
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This ioctl stores the state of the cpu at the guest real address given as
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argument, unless one of the following values defined in include/linux/kvm.h
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is given as argument:
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KVM_S390_STORE_STATUS_NOADDR - the CPU stores its status to the save area in
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absolute lowcore as defined by the principles of operation
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KVM_S390_STORE_STATUS_PREFIXED - the CPU stores its status to the save area in
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its prefix page just like the dump tool that comes with zipl. This is useful
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to create a system dump for use with lkcdutils or crash.
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ioctl: KVM_S390_SET_INITIAL_PSW
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args: struct kvm_s390_psw *
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see also: include/linux/kvm.h
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This ioctl can be used to set the processor status word (psw) of a stopped cpu
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prior to running it with KVM_RUN. Note that this call is not required to modify
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the psw during sie intercepts that fall back to userspace because struct kvm_run
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does contain the psw, and this value is evaluated during reentry of KVM_RUN
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after the intercept exit was recognized.
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ioctl: KVM_S390_INITIAL_RESET
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args: none
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see also: include/linux/kvm.h
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This ioctl can be used to perform an initial cpu reset as defined by the
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principles of operation. The target cpu has to be in stopped state.
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