[patch 3/3] KVM: x86: zero kvmclock_offset when vcpu0 initializes kvmclock system MSR

[Marcelo Tosatti <mtosatti@redhat.com>]

[-- Attachment #1: 03-host-patch --]
[-- Type: text/plain, Size: 1038 bytes --]

Initialize kvmclock base, on kvmclock system MSR write time,
so that the guest sees kvmclock counting from zero.

This matches baremetal behaviour when kvmclock in guest
sets sched clock stable.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

---
 arch/x86/kvm/x86.c |    5 +++++
 1 file changed, 5 insertions(+)

Index: kvm/arch/x86/kvm/x86.c
===================================================================
--- kvm.orig/arch/x86/kvm/x86.c	2015-05-27 17:40:46.948189811 -0300
+++ kvm/arch/x86/kvm/x86.c	2015-05-27 22:43:47.340413347 -0300
@@ -1703,6 +1703,8 @@
 	/* If the host uses TSC clocksource, then it is stable */
 	if (use_master_clock)
 		pvclock_flags |= PVCLOCK_TSC_STABLE_BIT;
+	if (ka->kvmclk_counts_from_zero)
+		pvclock_flags |= PVCLOCK_COUNTS_FROM_ZERO;
 
 	vcpu->hv_clock.flags = pvclock_flags;
 
@@ -2282,6 +2284,9 @@
 					&vcpu->requests);
 
 			ka->boot_vcpu_runs_old_kvmclock = tmp;
+
+			ka->kvmclock_offset = -get_kernel_ns();
+			ka->kvmclk_counts_from_zero = true;
 		}
 
 		vcpu->arch.time = data;