[10/18] Keep SMP VMs more in sync on unstable TSC

Commit Message

Zachary Amsden July 13, 2010, 2:25 a.m. UTC

None

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 324e892..d9e0aa0 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -339,6 +339,7 @@  struct kvm_vcpu_arch {
 	unsigned int time_offset;
 	struct page *time_page;
 	u64 last_host_tsc;
+	u64 last_host_ns;
 
 	bool nmi_pending;
 	bool nmi_injected;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 51d3f3e..a4d7cb9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1888,8 +1888,13 @@  void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 				native_read_tsc() - vcpu->arch.last_host_tsc;
 		if (tsc_delta < 0)
 			mark_tsc_unstable("KVM discovered backwards TSC");
-		if (check_tsc_unstable())
+		if (check_tsc_unstable()) {
+			/* Subtract elapsed cycle time */
+			u64 ns = !vcpu->arch.last_host_ns ? 0 :
+				  get_kernel_ns() - vcpu->arch.last_host_ns;
+			tsc_delta -= nsec_to_cycles(ns);
 			kvm_x86_ops->adjust_tsc_offset(vcpu, -tsc_delta);
+		}
 		kvm_migrate_timers(vcpu);
 		kvm_request_guest_time_update(vcpu);
 		vcpu->cpu = cpu;
@@ -1901,6 +1906,7 @@  void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 	kvm_x86_ops->vcpu_put(vcpu);
 	kvm_put_guest_fpu(vcpu);
 	vcpu->arch.last_host_tsc = native_read_tsc();
+	vcpu->arch.last_host_ns = get_kernel_ns();
 }
 
 static int is_efer_nx(void)