2017-07-04 12:24+0800, Wanpeng Li: > I observed that the hang during the boot of guest since pvspinlock > depends on trapping the halt as mentioned in this patch: > http://lkml.iu.edu/hypermail/linux/kernel/1202.0/03309.html，the hang > disappears when I remove the KVM_FEATURE_PV_UNHALT CPUID flag in order > to disable the pvspinlock in guest from kvm. So if disable the > pvspinlock in the low latency scenario(idle=poll in guest) w/ vCPU and > pCPU 1:1 pin can be acceptable? I think the hang happened because one VCPU did a halt with disabled interrupts and then ignored KVM_HC_KICK_CPU from another VCPU. The target VCPU does a VM exit, so handling the PV unhalt should be a simple setting of GUEST_ACTIVITY_ACTIVE upon arch.pv.pv_unhalted. If it turns out to be complicated, then forbidding the userspace to configure both is acceptable, (like you said, it currently doesn't make much sense to combine them) thanks.
