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    Subject[PATCH RFC V6 5/5] Documentation/kvm : Add documentation on Hypercalls and features used for PV spinlock
    From: Raghavendra K T <> 

    KVM_HC_KICK_CPU hypercall added to wakeup halted vcpu in paravirtual spinlock
    enabled guest.

    KVM_FEATURE_PV_UNHALT enables guest to check whether pv spinlock can be enabled
    in guest. support in host is queried via

    Thanks Alex for KVM_HC_FEATURES inputs and Vatsa for rewriting KVM_HC_KICK_CPU

    Signed-off-by: Srivatsa Vaddagiri <>
    Signed-off-by: Raghavendra K T <>
    diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
    index 6386f8c..7e2eba0 100644
    --- a/Documentation/virtual/kvm/api.txt
    +++ b/Documentation/virtual/kvm/api.txt
    @@ -1119,6 +1119,13 @@ support. Instead it is reported via
    if that returns true and you use KVM_CREATE_IRQCHIP, or if you emulate the
    feature in userspace, then you can enable the feature for KVM_SET_CPUID2.

    +Paravirtualized ticket spinlocks can be enabled in guest by checking whether
    +support exists in host via,
    +if this call return true, guest can use the feature.

    Capability: KVM_CAP_PPC_GET_PVINFO
    diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
    index 8820685..062dff9 100644
    --- a/Documentation/virtual/kvm/cpuid.txt
    +++ b/Documentation/virtual/kvm/cpuid.txt
    @@ -39,6 +39,10 @@ KVM_FEATURE_CLOCKSOURCE2 || 3 || kvmclock available at msrs
    KVM_FEATURE_ASYNC_PF || 4 || async pf can be enabled by
    || || writing to msr 0x4b564d02
    +KVM_FEATURE_PV_UNHALT || 6 || guest checks this feature bit
    + || || before enabling paravirtualized
    + || || spinlock support.
    KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side
    || || per-cpu warps are expected in
    || || kvmclock.
    diff --git a/Documentation/virtual/kvm/hypercalls.txt b/Documentation/virtual/kvm/hypercalls.txt
    new file mode 100644
    index 0000000..c9e8b9c
    --- /dev/null
    +++ b/Documentation/virtual/kvm/hypercalls.txt
    @@ -0,0 +1,59 @@
    +KVM Hypercalls Documentation
    +Template for documentation is
    +The documenenation for hypercalls should inlcude
    +1. Hypercall name, value.
    +2. Architecture(s)
    +3. status (deprecated, obsolete, active)
    +4. Purpose
    +value: 1
    +Architecture: x86
    +2. KVM_HC_MMU_OP
    +value: 2
    +Architecture: x86
    +status: deprecated.
    +Purpose: Support MMU operations such as writing to PTE,
    +flushing TLB, release PT.
    +value: 3
    +Architecture: PPC
    +Purpose: Expose hypercall availability to the guest. On x86 platforms, cpuid
    +used to enumerate which hypercalls are available. On PPC, either device tree
    +based lookup ( which is also what EPAPR dictates) OR KVM specific enumeration
    +mechanism (which is this hypercall) can be used.
    +value: 4
    +Architecture: PPC
    +Purpose: To enable communication between the hypervisor and guest there is a
    +shared page that contains parts of supervisor visible register state.
    +The guest can map this shared page to access its supervisor register through
    +memory using this hypercall.
    +value: 5
    +Architecture: x86
    +Purpose: Hypercall used to wakeup a vcpu from HLT state
    +Usage example : A vcpu of a paravirtualized guest that is busywaiting in guest
    +kernel mode for an event to occur (ex: a spinlock to become available) can
    +execute HLT instruction once it has busy-waited for more than a threshold
    +time-interval. Execution of HLT instruction would cause the hypervisor to put
    +the vcpu to sleep until occurence of an appropriate event. Another vcpu of the
    +same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall,
    +specifying APIC ID of the vcpu to be wokenup.
    +1. more information on input and output needed?
    +2. Add more detail to purpose of hypercalls.

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