On 11/19/19 11:36 AM, Wanpeng Li wrote: > On Tue, 12 Nov 2019 at 01:23, Joao Martins <joao.m.martins@xxxxxxxxxx> wrote: >> >> While vCPU is blocked (in kvm_vcpu_block()), it may be preempted which >> will cause vmx_vcpu_pi_put() to set PID.SN. If later the vCPU will be > > How can this happen? See the prepare_to_swait_exlusive() in > kvm_vcpu_block(), the task will be set in TASK_INTERRUPTIBLE state, > kvm_sched_out will set vcpu->preempted to true iff current->state == > TASK_RUNNING. You're right. But preemption (thus setting PID.SN) can still happen before vcpu_block(), or otherwise scheduled out if we are already in vcpu_block() (with task in TASK_INTERRUPTIBLE). The right term we should have written in that sentence above would have been 'scheduled out' and drop the vcpu_block mention and it would encompass both cases. A better sentence would perhaps be: "While vCPU is blocked (or about to block) it may be scheduled out which will cause vmx_vcpu_pi_put() to be called." But setting or not preempted/PID.SN doesn't change the rest and was mentioned for completeness. Joao
