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

[Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>]

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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