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by baobrien
2894 days ago
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> separate hypervisor mode RISC-V, without the hypervisor extension, meets the requirements for Popek-Goldberg virtualization, unlike x86. The problem is that classic virtualization requires shadow paging for memory virtualization, which can be slow. The hypervisor extension (not yet finalized) only adds two level nested paging, a few shadow CSRs, and IIRC a few more interrupt handling registers. The hypervisor extension itself is virtualizable (again, with shadow page tables). |
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Right, I forgot about RISC-V's MSR equivalent - with a worse assembler implementation (though that's simple to fix without touching the ISA) since the standard assembly expects them to be names, not numbers (that can be #defined away to names).
I had a (very emphatically not) fun time updating coreboot's toolchain and code base in lock step to ensure that risc-v code remained compilable when these changed.