On Thu, Feb 24, 2022, Varad Gautam wrote: > Processing #VC exceptions on AMD SEV-ES requires instruction decoding > logic to set up the right GHCB state before exiting to the host. > > Pull in the instruction decoder from Linux for this purpose. Do we really need Linux's decoder for this? Linux needs a more robust decoder because it has to deal with userspace crud, but KUT should have full control over what code it encounters in a #VC handler, e.g. we should never have to worry about ignore prefixes on a WRMSR. And looking at future patches, KUT is still looking at raw opcode bytes, e.g. /* Is it a WRMSR? */ exit_info_1 = (ctxt->insn.opcode.bytes[1] == 0x30) ? 1 : 0; and the giant switch in vc_ioio_exitinfo(). The decoder does bring a bit of cleanliness, but 2k+ lines of code that's likely to get stale fairly quickly is going to be a maintenance burden. And we certainly don't need things like VEX prefix handling :-) Do you happen to have data on how often each flavors of instructions is encountered? E.g. can we get away with a truly minimal "decoder" by modifying select tests to avoid hard-to-decode instructions? Or even patch them to do VMGEXIT directly?
