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. -- 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
