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authorRaghavendra K T <raghavendra.kt@linux.vnet.ibm.com>2013-08-26 14:18:36 +0530
committerGleb Natapov <gleb@redhat.com>2013-08-26 12:47:49 +0300
commit9bc6cbebfe006bcf0f83b10221cd4b893a130d10 (patch)
tree957ba8780239c78fdea13ceb78327c3652a9303f
parent24d2166beb2f0be7dd29ab6a0841c27bd669eae9 (diff)
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@landley.net> Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com> Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> Acked-by: Gleb Natapov <gleb@redhat.com> Acked-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Gleb Natapov <gleb@redhat.com>
-rw-r--r--Documentation/virtual/kvm/cpuid.txt4
-rw-r--r--Documentation/virtual/kvm/hypercalls.txt14
2 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
index 83afe65d4966..22ff659bc0fb 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 ea113b5d87a4..022198e389d7 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.