Messages in this thread | | | Date | Fri, 01 Aug 2014 08:35:03 +0200 | From | Paolo Bonzini <> | Subject | Re: [PATCH] KVM: nVMX: nested TPR shadow/threshold emulation |
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Il 01/08/2014 02:57, Zhang, Yang Z ha scritto: > > TPR_THRESHOLD will be likely written as zero, but the processor will > > never use it anyway. It's just a small optimization because > > nested_cpu_has(vmcs12, CPU_BASED_TPR_SHADOW) will almost always be true. > > Theoretically, you are right. But we should not expect all VMMs > follow it. It is not worth to violate the SDM just for saving two or > three instructions' cost.
Yes, you do need an "if (cpu_has_vmx_tpr_shadow())" around the vmcs_write32. But still, checking nested_cpu_has is not strictly necessary. Right now they both are a single AND, but I have plans to change all of the cpu_has_*() checks to static keys.
Paolo
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