From: Wanpeng Li Date: Tue, 30 Aug 2016 08:14:00 +0000 (+0800) Subject: KVM: lapic: adjust preemption timer correctly when goes TSC backward X-Git-Tag: v4.8-rc7~33^2~3 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=e12c8f36f3f7a60d55938c5aed5999278fa92bcb;p=karo-tx-linux.git KVM: lapic: adjust preemption timer correctly when goes TSC backward TSC_OFFSET will be adjusted if discovers TSC backward during vCPU load. The preemption timer, which relies on the guest tsc to reprogram its preemption timer value, is also reprogrammed if vCPU is scheded in to a different pCPU. However, the current implementation reprogram preemption timer before TSC_OFFSET is adjusted to the right value, resulting in the preemption timer firing prematurely. This patch fix it by adjusting TSC_OFFSET before reprogramming preemption timer if TSC backward. Cc: Paolo Bonzini Cc: Radim Krċmář Cc: Yunhong Jiang Signed-off-by: Wanpeng Li Signed-off-by: Paolo Bonzini --- diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 19f9f9e05c2a..699f8726539a 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2743,16 +2743,16 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) if (tsc_delta < 0) mark_tsc_unstable("KVM discovered backwards TSC"); - if (kvm_lapic_hv_timer_in_use(vcpu) && - kvm_x86_ops->set_hv_timer(vcpu, - kvm_get_lapic_tscdeadline_msr(vcpu))) - kvm_lapic_switch_to_sw_timer(vcpu); if (check_tsc_unstable()) { u64 offset = kvm_compute_tsc_offset(vcpu, vcpu->arch.last_guest_tsc); kvm_x86_ops->write_tsc_offset(vcpu, offset); vcpu->arch.tsc_catchup = 1; } + if (kvm_lapic_hv_timer_in_use(vcpu) && + kvm_x86_ops->set_hv_timer(vcpu, + kvm_get_lapic_tscdeadline_msr(vcpu))) + kvm_lapic_switch_to_sw_timer(vcpu); /* * On a host with synchronized TSC, there is no need to update * kvmclock on vcpu->cpu migration