On Fri, Aug 23, 2019 at 04:47:14PM +0300, Liran Alon wrote: > > > > On 23 Aug 2019, at 4:07, Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote: > > > > Add an explicit emulation type for forced #UD emulation and use it to > > detect that KVM should unconditionally inject a #UD instead of falling > > into its standard emulation failure handling. > > > > Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> > > The name "forced emulation on #UD" is not clear to me. > > If I understand correctly, EMULTYPE_TRAP_UD is currently used to indicate > that in case the x86 emulator fails to decode instruction, the caller would > like the x86 emulator to fail early such that it can handle this condition > properly. Thus, I would rename it EMULTYPE_TRAP_DECODE_FAILURE. EMULTYPE_TRAP_UD is used when KVM intercepts a #UD from hardware. KVM only emulates select instructions in this case in order to minmize the emulator attack surface, e.g.: if (unlikely(ctxt->ud) && likely(!(ctxt->d & EmulateOnUD))) return EMULATION_FAILED; To enable testing of the emulator, KVM recognizes a special "opcode" that triggers full emulation on #UD, e.g. ctxt->ud is false when the #UD was triggered with the magic prefix. The prefix is only recognized when the module param force_emulation_prefix is toggled on, hence the name EMULTYPE_TRAP_UD_FORCED. > But this new flag seems to do the same. So I’m left confused. I’m probably > missing something trivial here.
