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SubjectRe: [PATCH RFC V9 18/19] Documentation/kvm : Add documentation on Hypercalls and features used for PV spinlock
On Sun, Jun 02, 2013 at 12:56:24AM +0530, Raghavendra K T wrote:
> Documentation/kvm : Add documentation on Hypercalls and features used for PV spinlock
>
> From: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
>
> 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.
>
> Thanks Vatsa for rewriting KVM_HC_KICK_CPU
>
> Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
> Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
> ---
> Documentation/virtual/kvm/cpuid.txt | 4 ++++
> Documentation/virtual/kvm/hypercalls.txt | 13 +++++++++++++
> 2 files changed, 17 insertions(+)
>
> diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
> index 83afe65..654f43c 100644
> --- a/Documentation/virtual/kvm/cpuid.txt
> +++ b/Documentation/virtual/kvm/cpuid.txt
> @@ -43,6 +43,10 @@ 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
> index ea113b5..2a4da11 100644
> --- a/Documentation/virtual/kvm/hypercalls.txt
> +++ b/Documentation/virtual/kvm/hypercalls.txt
> @@ -64,3 +64,16 @@ 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.
> +
> +5. KVM_HC_KICK_CPU
> +------------------------
> +Architecture: x86
> +Status: active
> +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.

woken up.
>


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