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Executing real mode instructions inside virtualization extensions wasn't supported until Sandy Bridge/Westmere (called "Unrestricted Guest"). AMD Zen has it as
by Teknoman117 5y ago
Executing real mode instructions inside virtualization extensions wasn't supported until Sandy Bridge/Westmere (called "Unrestricted Guest"). AMD Zen has it as well, not sure if any of the FX processors had it. Before then, the real mode init of a virtual machine had to be handled via software emulation.
edit - remove nitpick about this not being vm86 mode because I missed the hypervisor bit in the parent comment.
- monocasa 5y agoAll of the AMD SVM cores supported real mode in guests as far as I know, and Sandy Bridge is a decade old at this point. But yeah, that was really annoying, retconned "restricted guest" would happily let you put real mode segment info into the VMCS, but just silently would be broken in goofy ways. I tore my hair out for a while writing a hypervisor back then that was intending on running some real mode code until I figured out what was going on.
- rnd0 5y agoMy question is -are these extentions part of the features in newer CPUs that are being exploited like Spectre etc or is it completely unrelated. I ask because if it is, then it may be a feature (or set of features) that's going to be going away. [edited in hopes of being clearer]
- monocasa 5y agoIt's unrelated to spectre-like vulnerabilities.