[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] rdtscp on HVM domains
I've just discovered that the rdtscp instruction doesn't work at all in a VMX (Intel HVM) domain, even on a Nehalem physical machine that supports the rdtscp instruction in hardware. (I don't have an AMD machine handy to test... reading the code it appears to me it won't work there either, but I'm not positive.) Since Xen doesn't expose the rdtscp bit in cpuid, this may make sense, but the pvrdtscp algorithm asks Xen directly whether the physical machine supports rdtscp and then uses the rdtscp instruction if Xen answers yes. Ideally, we'd like to allow these enterprise apps to work (fast and correctly) both on PV and HVM. So questions for VMX/SVM experts: 1) Is it possible for VMX (and SVM) to allow rdtscp to execute natively on machines that support it without exposing the rdtscp bit in cpuid? 2) Is it possible for VMX (and SVM) to trap and emulate rdtscp on machines that DON'T support rdtscp? Thanks, Dan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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