linux-kernel - [PATCH RFC V8 17/17] Documentation/kvm : Add documentation on Hypercalls and features used for PV spinlock

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Message-Id: <20120502100947.13206.26518.sendpatchset@codeblue.in.ibm.com>
Date:	Wed, 02 May 2012 15:39:47 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"H. Peter Anvin" <hpa@...or.com>, Avi Kivity <avi@...hat.com>,
	X86 <x86@...nel.org>, Gleb Natapov <gleb@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	Attilio Rao <attilio.rao@...rix.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	linux-doc@...r.kernel.org,
	Virtualization <virtualization@...ts.linux-foundation.org>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	KVM <kvm@...r.kernel.org>, Andi Kleen <andi@...stfloor.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Stephan Diestelhorst <stephan.diestelhorst@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH RFC V8 17/17] 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 Alex for KVM_HC_FEATURES inputs and 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 |   60 ++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+), 0 deletions(-)
diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
index 8820685..062dff9 100644
--- a/Documentation/virtual/kvm/cpuid.txt
+++ b/Documentation/virtual/kvm/cpuid.txt
@@ -39,6 +39,10 @@ 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
new file mode 100644
index 0000000..bc3f14a
--- /dev/null
+++ b/Documentation/virtual/kvm/hypercalls.txt
@@ -0,0 +1,60 @@
+KVM Hypercalls Documentation
+===========================
+The template for each hypercall is:
+1. Hypercall name, value.
+2. Architecture(s)
+3. Status (deprecated, obsolete, active)
+4. Purpose
+
+1. KVM_HC_VAPIC_POLL_IRQ
+------------------------
+Value: 1
+Architecture: x86
+Purpose: None
+
+2. KVM_HC_MMU_OP
+------------------------
+Value: 2
+Architecture: x86
+Status: deprecated.
+Purpose: Support MMU operations such as writing to PTE,
+flushing TLB, release PT.
+
+3. KVM_HC_FEATURES
+------------------------
+Value: 3
+Architecture: PPC
+Status: active
+Purpose: Expose hypercall availability to the guest. On x86 platforms, cpuid
+used to enumerate which hypercalls are available. On PPC, either device tree
+based lookup ( which is also what EPAPR dictates) OR KVM specific enumeration
+mechanism (which is this hypercall) can be used.
+
+4. KVM_HC_PPC_MAP_MAGIC_PAGE
+------------------------
+Value: 4
+Architecture: PPC
+Status: active
+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
+------------------------
+Value: 5
+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.
+
+TODO:
+1. more information on input and output needed?
+2. Add more detail to purpose of hypercalls.

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