On Wed, 2008-02-06 at 08:33 +0100, Guillaume Thouvenin wrote: > Hello, > > I read on the kvmwiki/TODO that there is a work in progress for > extending x86 emulator to support more instructions in real mode and for > changing the execution loop to call the emulator for real mode. > > As I'm interested to work on this part I'd like to know what was > already done.
cool! > > I'd like to have more information about how the execution loop need to > be changed. Currently we enter/leave real mode through a call to > enter_rmode()/enter_pmode(). The function sets a variable > "arch.rmode.active" and also sets the bit X86_EFLAGS_VM of > GUEST_RFLAGS. That means that we are using the VM mode to virtualize > the real mode. I know that in virtual mode some instructions can not be > used as they are in full real mode (that would have been too easy). So > these instructions generate a protection fault and need to be emulated. > So we handle this kind of exception in handle_exception() and we call > the x86 emulator. From the emulator we read the eflags > (kvm_x86_ops->get_rflags(vcpu)) and we can know if we are in real mode > or not. It's the current scheme, right? > > My question is why the execution loop needs to be changed here. I mean > isn't it possible to just extend x86 emulator to support more > instructions in real mode? I think that I'm missing something here so > any help, hint, advice, link are welcome. > > Best Regards, > i am not expert for the emulator area, but as far as i remember: virtual 8086 have some checks related to segments (the big mode problem), it mean that for some addresses it wont be able to execute anything, you will just get vmexit right away, therefor you need a full functional emulator that will handle everything there. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
