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. Jan
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