Re: [RFC/PATCH 12/15] kvm-s390: API documentation

Randy Dunlap
2008-03-20T17:22:00Z

On Thu, 20 Mar 2008 17:25:20 +0100 Carsten Otte wrote:

> This patch adds Documentation/s390/kvm.txt, which describes specifics of kvm's
> user interface that are unique to s390 architecture.
>
> Signed-off-by: Carsten Otte <cotte@de.ibm.com>
> ---
> Documentation/s390/kvm.txt | 125 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 125 insertions(+)
>
> Index: kvm/Documentation/s390/kvm.txt
> ===================================================================
> --- /dev/null
> +++ kvm/Documentation/s390/kvm.txt
> @@ -0,0 +1,125 @@
> +*** BIG FAT WARNING ***
> +The kvm module is currently in EXPERIMENTAL state for s390. This means, that

This means that [no comma]

> +the interface to the module is not yet considered to remain stable. Thus, be
> +prepared that we keep breaking your userspace application and guest
> +compatibility over and over again until we feel happy with the result. Make sure
> +your guest kernel, your host kernel, and your userspace launcher are in a
> +consistent state.
> +
> +This Documentation describes the unique ioctl calls to /dev/kvm, the resulting
> +kvm-vm file descriptors, and the kvm-vcpu file descriptors that differ from x86.
> +
> +1. ioctl calls to /dev/kvm
> +KVM does support the following ioctls on s390 that are common with other
> +architectures and do behave the same:
> +KVM_GET_API_VERSION
> +KVM_CREATE_VM (*) see note
> +KVM_CHECK_EXTENSION
> +KVM_GET_VCPU_MMAP_SIZE
> +
> +Notes:
> +* KVM_CREATE_VM may fail on s390, if the calling process has multiple
> +threads and has not called KVM_S390_ENABLE_SIE before.
> +
> +In addition, on s390 the following architecture specific ioctls are supported:
> +ioctl: KVM_S390_ENABLE_SIE
> +args: none
> +see also: include/linux/kvm.h
> +This call causes the kernel to switch on PGSTE in the user page table. This
> +operation is needed in order to run a virtual machine, and it requires the
> +calling process to be single-threaded. Note that the first call to KVM_CREATE_VM
> +will implicitly try to switch on PGSTE if the user process has not called
> +KVM_S390_ENABLE_SIE before. User processes that want to launch multiple threads
> +before creating a virtual machine have to call KVM_S390_ENABLE_SIE, or will
> +observe an error calling KVM_CREATE_VM. Switching on PGSTE is a one-time
> +operation, is not reversible, and will persist over the entire lifetime of
> +the calling process. It does not have any user-visibe effect other than a small

user-visible

> +performance penalty.
> +
> +2. ioctl calls to the kvm-vm file descriptor
> +KVM does support the following ioctls on s390 that are common with other
> +architectures and do behave the same:
> +KVM_CREATE_VCPU
> +KVM_SET_USER_MEMORY_REGION (*) see note
> +KVM_GET_DIRTY_LOG (**) see note
> +
> +Notes:
> +* kvm does only allow exactly one memory slot on s390, which has to start
> + at guest absolute address zero and at a user address that is aligned on any
> + page boundary. This hardware "limitation" allows us to have a few unique
> + optimizations. The memory slot does'nt have to be filled

doesn't

> + with memory actually, it may contain sparse holes. That said, with different
> + user memory layout this does still allow a large flexibility when
> + doing the guest memory setup.
> +** KVM_GET_DIRTY_LOG does'nt work proper yet. The user will receive an empty

doesn't work properly

> +log. This ioctl call is only needed for guest migration, and we intend to
> +implement this one in the future.
> +
> +In addition, on s390 the following architecture specific ioctls for the kvm-vm
> +file descriptor are supported:
> +ioctl: KVM_S390_INTERRUPT
> +args: struct kvm_s390_interrupt *
> +see also: include/linux/kvm.h
> +This ioctl is used to submit a floating interrupt for a virtual machine.
> +Floating interrupts may be delivered to any virtual cpu in the configuration.
> +Only some interrupt types defined in include/linux/kvm.h make sense when
> +submitted as floating interrupt. The following interrupts are not considered

interrupts.

> +to be useful as floating interrupt, and a call to inject them will result in

interrupts,

> +-EINVAL error code: program interrupts, and interprocessor signals. Valid

no comma

> +floating interrupts are:
> +KVM_S390_INT_VIRTIO
> +KVM_S390_INT_SERVICE
> +
> +3. ioctl calls to the kvm-vcpu file descriptor
> +KVM does support the following ioctls on s390 that are common with other
> +architectures and do behave the same:
> +KVM_RUN
> +KVM_GET_REGS
> +KVM_SET_REGS
> +KVM_GET_SREGS
> +KVM_SET_SREGS
> +KVM_GET_FPU
> +KVM_SET_FPU
> +
> +In addition, on s390 the following architecture specific ioctls for the
> +kvm-vcpu file descriptor are supported:
> +ioctl: KVM_S390_INTERRUPT
> +args: struct kvm_s390_interrupt *
> +see also: include/linux/kvm.h
> +This ioctl is used to submit an interrupt for a specific virtual cpu.
> +Only some interrupt types defined in include/linux/kvm.h make sense when
> +submitted for a specific cpu. The following interrupts are not considered
> +to be useful, and a call to inject them will result in -EINVAL error code:
> +service processor calls, and virtio interrupts. Valid interrupt types are:

no comma

> +KVM_S390_PROGRAM_INT
> +KVM_S390_SIGP_STOP
> +KVM_S390_RESTART
> +KVM_S390_SIGP_SET_PREFIX
> +KVM_S390_INT_EMERGENCY
> +
> +ioctl: KVM_S390_STORE_STATUS
> +args: unsigned long
> +see also: include/linux/kvm.h
> +This ioctl stores the state of the cpu at the guest real address given as
> +argument, unless one of the following values defined in include/linux/kvm.h
> +is given as arguement:
> +KVM_S390_STORE_STATUS_NOADDR - the CPU stores its status to the save area in
> +absolute lowcore as defined by the principles of operation
> +KVM_S390_STORE_STATUS_PREFIXED - the CPU stores its status to the save area in
> +its prefix page just like the dump tool that comes with zipl. This is useful
> +to create a system dump for use with lkcdutils or crash.
> +
> +ioctl: KVM_S390_SET_INITIAL_PSW
> +args: struct kvm_s390_psw *
> +see also: include/linux/kvm.h
> +This ioctl can be used to set the processor status word (psw) of a stopped cpu
> +prior to running it with KVM_RUN. Note that this call is not required to modify
> +the psw during sie intercepts that fall back to userspace because struct kvm_run
> +does contain the psw, and this value is evaluated during reentry of KVM_RUN
> +after the intercept exit was recognized.
> +
> +ioctl: KVM_S390_INITIAL_RESET
> +args: none
> +see also: include/linux/kvm.h
> +This ioctl can be used to perform an initial cpu reset as defined by the
> +principles of operation. The target cpu has to be in stopped state.

---
~Randy