>Note, kvm_use_posted_timer_interrupt() uses a heuristic of HLT/MWAIT interception >being disabled to detect that it's worth trying to post a timer interrupt, but off >the top of my head I'm pretty sure that's unnecessary and pointless. The Commit 1714a4eb6fb0 gives an explanation: if only some guests isolated and others not, they would not have any benefit from posted timer interrupts, and at the same time lose VMX preemption timer fast paths because kvm_can_post_timer_interrupt() returns true and therefore forces kvm_can_use_hv_timer() to false. >"vcpu->mode == IN_GUEST_MODE" is super cheap, and I can't think of any harm in >posting the time interrupt if the target vCPU happens to be in guest mode even >if the host wasn't configured just so. > >> Another scenario I was thinking of was hrtimer expiry during vcpu exit >> being handled in KVM/userspace, which will cause timer interrupt >> injection after the next exit [1] delaying timer interrupt to guest. > >No, the IRQ won't be delayed. Expiration from the hrtimer callback will set >KVM_REQ_UNBLOCK, which will prevent actually entering the guest (see the call >to kvm_request_pending() in kvm_vcpu_exit_request()). > >> This scenario is not specific to TDX VMs though. >> >> [1] https://git.kernel.org/pub/scm/virt/kvm/kvm.git/tree/arch/x86/kvm/x86.c?h=kvm-coco-queue#n11263
