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

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On 06/03/2013 09:34 PM, Konrad Rzeszutek Wilk wrote:
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.

Yep. :)

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