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System Management Mode (SMM) is a special x86 processor mode that privileged software such as kernels or hypervisors cannot access or interrupt. Previously, it has been assumed that time spent in SMM would be relatively small and therefore its side effects on privileged software were unimportant; recently, researchers have proposed uses, such as security-related checks, that would greatly increase the amount of runtime spent in this mode. We present the results of a detailed performance study to characterize the performance impacts of SMM, using measurement infrastructure we have developed. Our study includes impact to application, system, and hypervisor. We show there can be clear negative effects from prolonged preemptions. However, if SMM duration is kept within certain ranges, perturbation caused by SMIs may be kept to a minimum. |
