Revert "KVM: x86: zero kvmclock_offset when vcpu0 initializes kvmclock system MSR"

Shifting pvclock_vcpu_time_info.system_time on write to KVM system time
MSR is a change of ABI.  Probably only 2.6.16 based SLES 10 breaks due
to its custom enhancements to kvmclock, but KVM never declared the MSR
only for one-shot initialization.  (Doc says that only one write is
needed.)

This reverts commit b7e60c5aedd2b63f16ef06fde4f81ca032211bc5.
And adds a note to the definition of PVCLOCK_COUNTS_FROM_ZERO.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Acked-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 1 insertions, 4 deletions

diff --git a/arch/x86/include/asm/pvclock-abi.h b/arch/x86/include/asm/pvclock-abi.h
index 655e07a48f6c..67f08230103a 100644
--- a/arch/x86/include/asm/pvclock-abi.h
+++ b/arch/x86/include/asm/pvclock-abi.h
@@ -41,6 +41,7 @@ struct pvclock_wall_clock {
 
 #define PVCLOCK_TSC_STABLE_BIT  (1 << 0)
 #define PVCLOCK_GUEST_STOPPED   (1 << 1)
+/* PVCLOCK_COUNTS_FROM_ZERO broke ABI and can't be used anymore. */
 #define PVCLOCK_COUNTS_FROM_ZERO (1 << 2)
 #endif /* __ASSEMBLY__ */
 #endif /* _ASM_X86_PVCLOCK_ABI_H */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 991466bf8dee..92511d4b7236 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1708,8 +1708,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
                 vcpu->pvclock_set_guest_stopped_request = false;
         }
 
-        pvclock_flags |= PVCLOCK_COUNTS_FROM_ZERO;
-
         /* If the host uses TSC clocksource, then it is stable */
         if (use_master_clock)
                 pvclock_flags |= PVCLOCK_TSC_STABLE_BIT;
@@ -2007,8 +2005,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                                         &vcpu->requests);
 
                         ka->boot_vcpu_runs_old_kvmclock = tmp;
-
-                        ka->kvmclock_offset = -get_kernel_ns();
                 }
 
                 vcpu->arch.time = data;