Re: [PATCH RFC V3 2/4] kvm hypervisor : Add a hypercall to KVM hypervisor to support pv-ticketlocks

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[ CCing Jeremy's new email ID ]
Hi Avi,
Thanks for review and inputs.

On 12/01/2011 04:41 PM, Avi Kivity wrote:
On 11/30/2011 10:59 AM, Raghavendra K T wrote:

The hypercall needs to be documented in
Documentation/virtual/kvm/hypercalls.txt.


Yes, Sure 'll document. hypercalls.txt is a new file right?. also I have to document APIs in Documentation/virtual/kvm/api.txt.

Have you tested it on AMD machines?  There are some differences in the
hypercall infrastructure there.

Yes. 'll test on AMD machine and update on that.


  /* This indicates that the new set of kvmclock msrs
   * are available. The use of 0x11 and 0x12 is deprecated
   */
  #define KVM_FEATURE_CLOCKSOURCE2        3
  #define KVM_FEATURE_ASYNC_PF		4
  #define KVM_FEATURE_STEAL_TIME		5
+#define KVM_FEATURE_KICK_VCPU		6

Documentation/virtual/kvm/cpuid.txt.

Yes. 'll do that.



  /* The last 8 bits are used to indicate how to interpret the flags field
   * in pvclock structure. If no bits are set, all flags are ignored.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c38efd7..6e1c8b4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2103,6 +2103,7 @@ int kvm_dev_ioctl_check_extension(long ext)
  	case KVM_CAP_XSAVE:
  	case KVM_CAP_ASYNC_PF:
  	case KVM_CAP_GET_TSC_KHZ:
+	case KVM_CAP_KICK_VCPU:

This is redundant with the feature bit?  In general, KVM_CAP is for the
host API, while KVM_FEATURE is for the guest API.


No its not. I have to check the flow again. I understood that this completes the guest querying, that checks for KVM_FEATURE availability.
Did I miss something? I need a little deep dive though.


+/*
+ * kvm_pv_kick_cpu_op:  Kick a vcpu.
+ *
+ * @cpu - vcpu to be kicked.
+ */
+static void kvm_pv_kick_cpu_op(struct kvm *kvm, int cpu)
+{
+	struct kvm_vcpu *vcpu = kvm_get_vcpu(kvm, cpu);

There is no guarantee that guest cpu numbers match host vcpu numbers.
Use APIC IDs, and kvm_apic_match_dest().

Okay. I have to dig more on this.


+	struct kvm_mp_state mp_state;
+
+	mp_state.mp_state = KVM_MP_STATE_RUNNABLE;
+	if (vcpu) {
+		vcpu->kicked = 1;
+		/* Ensure kicked is always set before wakeup */
+		barrier();
+	}
+	kvm_arch_vcpu_ioctl_set_mpstate(vcpu,&mp_state);

This must only be called from the vcpu thread.

Hmm. Okay. 'll check this.


+	kvm_vcpu_kick(vcpu);
+}
+

  	struct kvm_vcpu_arch arch;
+
+	/*
+	 * blocked vcpu wakes up by checking this flag set by unlocker.
+	 */
+	int kicked;


Write only variable.

Yes 'll remove comments.


An alternative approach is to use an MSR protocol like x2apic ICR.


'll explore on this too.

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