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

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Date:	Sun, 02 Jun 2013 00:56:24 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	<gleb@...hat.com>, <mingo@...hat.com>, <jeremy@...p.org>,
	<x86@...nel.org>, <konrad.wilk@...cle.com>, <hpa@...or.com>,
	<pbonzini@...hat.com>
Cc:	linux-doc@...r.kernel.org, <habanero@...ux.vnet.ibm.com>,
	Raghavendra K T <raghavendra.kt@...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: [PATCH RFC V9 18/19] Documentation/kvm : Add documentation on Hypercalls and features used for PV spinlock

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.

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