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SubjectRe: [PATCH] KVM: X86: Fix preempt the preemption timer cancel
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On 21/05/2017 05:32, Wanpeng Li wrote:
> CPU0 CPU1
>
> vmx_cancel_hv_timer
> vCPU0's vmx->hv_deadline_tsc = -1
>
> preempt occur
>
> clear preemption timer field in CPU1's active vmcs
> vCPU0's apic_timer.hv_timer_in_use = false
> vmx_vcpu_run(vCPU0)
> vmx_arm_hv_timer
> if (vmx->hv_deadline_tsc == -1)
> nothing change
>
> handle_preemption_timer(vCPU0)
> kvm_lapic_expired_hv_timer
> WARN_ON(!apic->lapic_timer.hv_timer_in_use);


I think it's more like this, what do you think?

CPU0 CPU1

preemption timer vmexit
handle_preemption_timer(vCPU0)
kvm_lapic_expired_hv_timer
vmx_cancel_hv_timer
vmx->hv_deadline_tsc = -1
vmcs_clear_bits
/* hv_timer_in_use still true */
sched_out
sched_in
kvm_arch_vcpu_load
vmx_set_hv_timer
write vmx->hv_deadline_tsc
vmcs_set_bits
/* back in kvm_lapic_expired_hv_timer */
hv_timer_in_use = false
...
vmx_vcpu_run
vmx_arm_hv_run
write preemption timer deadline
spurious preemption timer vmexit
handle_preemption_timer(vCPU0)
kvm_lapic_expired_hv_timer
WARN_ON(!apic->lapic_timer.hv_timer_in_use);


Thanks,

Paolo

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