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

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Date:	Mon, 3 Jun 2013 12:04:16 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Cc:	gleb@...hat.com, mingo@...hat.com, jeremy@...p.org, x86@...nel.org,
	hpa@...or.com, pbonzini@...hat.com, linux-doc@...r.kernel.org,
	habanero@...ux.vnet.ibm.com, xen-devel@...ts.xensource.com,
	peterz@...radead.org, mtosatti@...hat.com,
	stefano.stabellini@...citrix.com, andi@...stfloor.org,
	attilio.rao@...rix.com, ouyang@...pitt.edu, gregkh@...e.de,
	agraf@...e.de, chegu_vinod@...com, torvalds@...ux-foundation.org,
	avi.kivity@...il.com, tglx@...utronix.de, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, stephan.diestelhorst@....com,
	riel@...hat.com, drjones@...hat.com,
	virtualization@...ts.linux-foundation.org,
	srivatsa.vaddagiri@...il.com
Subject: Re: [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@...ux.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@...ux.vnet.ibm.com>
> Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.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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