On Sun, Feb 14, 2010 at 05:37:39PM +0100, Jan Kiszka wrote: > Gleb Natapov wrote: > > On Sun, Feb 14, 2010 at 12:39:14PM +0100, Jan Kiszka wrote: > >> Gleb Natapov wrote: > >>> On Sun, Feb 14, 2010 at 11:47:58AM +0100, Jan Kiszka wrote: > >>>> Gleb Natapov wrote: > >>>>> On Sun, Feb 14, 2010 at 11:26:31AM +0100, Jan Kiszka wrote: > >>>>>> Gleb Natapov wrote: > >>>>>>> On Sat, Feb 13, 2010 at 10:31:12AM +0100, Jan Kiszka wrote: > >>>>>>>> From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> > >>>>>>>> > >>>>>>>> We intercept #BP while in guest debugging mode. As VM exists due to > >>>>>>>> intercepted exceptions do not necessarily come with valid > >>>>>>>> idt_vectoring, we have to update event_exit_inst_len explicitly in such > >>>>>>>> cases. At least in the absence of migration, this ensures that > >>>>>>>> re-injections of #BP will find and use the correct instruction length. > >>>>>>>> > >>>>>>> event_exit_inst_len is only used for event reinjection. Since event > >>>>>>> intercepted here will not be reinjected why updating event_exit_inst_len > >>>>>>> is needed here? > >>>>>> In guest debugging mode a #BP exception is always reported to user space > >>>>>> to find out what caused it. If it was the guest itself, the exception is > >>>>>> reinjected, on older kernels via KVM_SET_GUEST_DEBUG and since 2.6.33 > >>>>>> via KVM_SET_VCPU_EVENTS (the latter requires some qemu patch that I will > >>>>>> post later). > >>>>>> > >>>>>> As we currently do not update event_exit_inst_len on #BP exits, > >>>>>> reinjecting fails unless event_exit_inst_len happens to be 1 from some > >>>>>> other exit. > >>>>>> > >>>>> Hmm, how does it work on SVM then where we do not have > >>>>> event_exit_inst_len so execution will resume on the same rip that caused > >>>>> #BP after event reinjection? > >>>>> > >>>> Maybe not at all. I don't think I've tested this scenario on amd so far. > >>>> Guess it needs some special handling in svm to move rip after the int3 > >>>> when requesting to inject #BP. > >>>> > >>> This will work for VMX too, no? So may be we should design something > >>> that will work for both VMX and SVM before applying patches that make > >>> oly VMX work? > >> VMX used to work, so my patch is actually a regression fix. I bet this > >> was accidentally broken while cleaning up the interrupt handling of VMX. > >> > > VMX used to always reexecute instruction. > > ...since 66fd3f7f90. And that was what broke this guest debugging corner > case. > I see. And I see why it worked, but it shouldn't have been working for SVM. I prefer to look for general solution here that works for SVM/VMX. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
