Messages in this thread | | | From | "Zhang, Yang Z" <> | Subject | RE: [PATCH] KVM: nVMX: nested TPR shadow/threshold emulation | Date | Fri, 1 Aug 2014 06:44:10 +0000 |
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Paolo Bonzini wrote on 2014-08-01: > 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.
See v2 patch. It isn't a problem anymore.
> > Paolo
Best regards, Yang
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