Re: [Xen-devel] [PATCH RFC V9 18/19] Documentation/kvm : Add documentation on Hypercalls and features used for PV spinlock

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

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@xxxxxxxxxxxxxxxxxx>
> 
> 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@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
> ---
>  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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