Messages in this thread | | | From | Paolo Bonzini <> | Subject | Re: [PATCH v2 1/2] KVM: SVM: Move asid to vcpu_svm | Date | Fri, 13 Nov 2020 18:03:40 +0100 |
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On 13/10/20 03:29, Sean Christopherson wrote: >> @@ -3446,6 +3447,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu) >> >> sync_lapic_to_cr8(vcpu); >> >> + svm->vmcb->control.asid = svm->asid; > > Related to the above, handling this in vcpu_run() feels wrong. There really > shouldn't be a need to track the ASID. vmcb01 will always exist if vmcb02 > exits, e.g. the ASID can be copied and marked dirty when loading vmcb02. > For new_asid(), it can unconditionally update vmcb01 and conditionally update > vmcb02.
Yeah, it is a bit ugly and it is only needed on processors without flush-by-ASID. On those processors the ASID is used by KVM as a sort of TLB flush generation count. A TLB flush should affect both VMCB01 and VMCB02, and that's the reason to have a global ASID in struct vcpu_svm.
On processors with flush-by-ASID, currently we bump the ASID on every physical CPU change. However even that is not needed, in principle svm->asid should never change and we could also have different ASID01 and ASID02, similar to VMX. So: long term, svm->asid should only be used only on processors without flush-by-ASID. kvm-amd however is not quite ready for that.
Paolo
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