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. Jan
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