On Thu, Oct 28, 2021, Maxim Levitsky wrote: > On Fri, 2021-10-08 at 19:12 -0700, Sean Christopherson wrote: > > Hoist the CPU => APIC ID conversion for the Posted Interrupt descriptor > > out of the loop to write the descriptor, preemption is disabled so the > > CPU won't change, and if the APIC ID changes KVM has bigger problems. > > > > No functional change intended. > > Is preemption always disabled in vmx_vcpu_pi_load? vmx_vcpu_pi_load is called > from vmx_vcpu_load, which is called indirectly from vcpu_load which is called > from many ioctls, which userspace does. In these places I don't think that > preemption is disabled. Preemption is disabled in vcpu_load() by the get_cpu(). The "cpu" param that's passed around the vcpu_load() stack is also why I think it's ok to _not_ assert that preemption is disabled in vmx_vcpu_pi_load(); if preemption is enabled, "cpu" is unstable and thus the entire "load" operation is busted. #define get_cpu() ({ preempt_disable(); __smp_processor_id(); }) #define put_cpu() preempt_enable() void vcpu_load(struct kvm_vcpu *vcpu) { int cpu = get_cpu(); __this_cpu_write(kvm_running_vcpu, vcpu); preempt_notifier_register(&vcpu->preempt_notifier); kvm_arch_vcpu_load(vcpu, cpu); put_cpu(); } EXPORT_SYMBOL_GPL(vcpu_load);