linux-kernel - [PATCH V13 4/4] Documentation/kvm : Add documentation on Hypercalls and features used for PV spinlock

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Date:	Mon, 26 Aug 2013 14:18:36 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	<mingo@...hat.com>, <hpa@...or.com>, <x86@...nel.org>,
	<gleb@...hat.com>, <pbonzini@...hat.com>
Cc:	<jeremy@...p.org>, <konrad.wilk@...cle.com>,
	<peterz@...radead.org>, <tglx@...utronix.de>, <agraf@...e.de>,
	digitaleric@...gle.com, <riel@...hat.com>, <avi.kivity@...il.com>,
	<habanero@...ux.vnet.ibm.com>, <chegu_vinod@...com>,
	<ouyang@...pitt.edu>, <drjones@...hat.com>,
	linux-doc@...r.kernel.org, <torvalds@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
	<andi@...stfloor.org>, <virtualization@...ts.linux-foundation.org>,
	<mtosatti@...hat.com>, <srivatsa.vaddagiri@...il.com>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Rob Landley <rob@...dley.net>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: [PATCH V13 4/4] Documentation/kvm : Add documentation on Hypercalls and features used for PV spinlock

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
Cc: Rob Landley <rob@...dley.net>
Signed-off-by: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Acked-by: Gleb Natapov <gleb@...hat.com>
Acked-by: Ingo Molnar <mingo@...nel.org>
---
 Documentation/virtual/kvm/cpuid.txt      |  4 ++++
 Documentation/virtual/kvm/hypercalls.txt | 14 ++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
index 83afe65..22ff659 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              ||     7 || 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..022198e 100644
--- a/Documentation/virtual/kvm/hypercalls.txt
+++ b/Documentation/virtual/kvm/hypercalls.txt
@@ -64,3 +64,17 @@ 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 (a1) of the vcpu to be woken up. An additional argument (a0)
+is used in the hypercall for future use.
-- 
1.7.11.7

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