Messages in this thread | | | Subject | Re: [PATCH v3 4/4] KVM: Add flush_on_enter before guest enter | From | Paolo Bonzini <> | Date | Fri, 10 Nov 2017 11:15:06 +0100 |
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On 10/11/2017 11:08, Peter Zijlstra wrote: > On Fri, Nov 10, 2017 at 01:49:47AM -0800, Wanpeng Li wrote: >> @@ -2887,7 +2899,7 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu) >> if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED)) >> return; >> >> - vcpu->arch.st.steal.preempted = KVM_VCPU_PREEMPTED; >> + vcpu->arch.st.steal.preempted |= KVM_VCPU_PREEMPTED; > > I don't understand this one... If there is concurrency its wrong, if > there is no concurrency it still doesn't make sense as there should not > be any FLUSH flags to preserve..
There is no concurrency, foreign VCPUs are not going to write to the location unless PREEMPTED is set. So indeed the "|=" is pointless.
However, I wonder if it'd be useful for a VCPU to set the bit _on itself_ before going to sleep. Like
set KVM_VCPU_SHOULD_FLUSH hlt /* Automagic TLB flush! */
This would not work currently, but if it *is* useful, we should make it work and document it as legal. Peter, do you think it would make any sense?
Thanks,
Paolo
>> >> kvm_write_guest_offset_cached(vcpu->kvm, &vcpu->arch.st.stime, >> &vcpu->arch.st.steal.preempted,
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