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authorAvi Kivity <avi@qumranet.com>2008-03-04 10:44:51 +0200
committerAvi Kivity <avi@qumranet.com>2008-04-27 11:53:27 +0300
commit019960ae9933161c2809fa4ee608ba30d9639fd2 (patch)
treec4ded864dfd339a2c64451220d0866eba854b63c
parentb8688d51bbe4872fbcec751e04369606082ac610 (diff)
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: Avi Kivity <avi@qumranet.com>
-rw-r--r--arch/x86/kvm/vmx.c9
1 files changed, 6 insertions, 3 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 7ef710afceb..fb0389d3a8d 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -519,7 +519,7 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
u64 phys_addr = __pa(vmx->vmcs);
- u64 tsc_this, delta;
+ u64 tsc_this, delta, new_offset;
if (vcpu->cpu != cpu) {
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.
*/
rdtscll(tsc_this);
- delta = vcpu->arch.host_tsc - tsc_this;
- vmcs_write64(TSC_OFFSET, vmcs_read64(TSC_OFFSET) + delta);
+ if (tsc_this < vcpu->arch.host_tsc) {
+ delta = vcpu->arch.host_tsc - tsc_this;
+ new_offset = vmcs_read64(TSC_OFFSET) + delta;
+ vmcs_write64(TSC_OFFSET, new_offset);
+ }
}
}