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Commit 019960ae authored by Avi Kivity's avatar Avi Kivity
Browse files

KVM: VMX: Don't adjust tsc offset forward 



Most Intel hosts have a stable tsc, and playing with the offset only
reduces accuracy.  By limiting tsc offset adjustment only to forward updates,
we effectively disable tsc offset adjustment on these hosts.

Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent b8688d51

arch/x86/kvm/vmx.c

+6 −3
Original line number Original line Diff line number Diff line
@@ -519,7 +519,7 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu) 
{

{

	struct vcpu_vmx *vmx = to_vmx(vcpu);

	struct vcpu_vmx *vmx = to_vmx(vcpu);

	u64 phys_addr = __pa(vmx->vmcs);

	u64 phys_addr = __pa(vmx->vmcs);

	u64 tsc_this, delta;

	u64 tsc_this, delta, new_offset;





	if (vcpu->cpu != cpu) {

	if (vcpu->cpu != cpu) {

		vcpu_clear(vmx);

		vcpu_clear(vmx);
@@ -559,8 +559,11 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu) 
		 * Make sure the time stamp counter is monotonous.

		 * Make sure the time stamp counter is monotonous.

		 */

		 */

		rdtscll(tsc_this);

		rdtscll(tsc_this);

		if (tsc_this < vcpu->arch.host_tsc) {

			delta = vcpu->arch.host_tsc - tsc_this;

			delta = vcpu->arch.host_tsc - tsc_this;

		vmcs_write64(TSC_OFFSET, vmcs_read64(TSC_OFFSET) + delta);

			new_offset = vmcs_read64(TSC_OFFSET) + delta;

			vmcs_write64(TSC_OFFSET, new_offset);

		}

	}

	}

}

}