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    SubjectRe: x86: do_debug && PTRACE_SINGLESTEP broken by 08d68323d1f0c34452e614263b212ca556dae47f
    On 12/19/2009 01:15 AM, Frederic Weisbecker wrote:
    >> Apparently it does. You should hack some printks into do_debug() and see
    >> how kvm is differing from real hardware. (Actually you can probably do
    >> this with a notifier added by a module, not that you are shy about
    >> recompiling!)
    >> Probably kvm's emulation of the hardware behavior wrt the DR6 bits is not
    >> sufficiently faithful. Conceivably, kvm is being consistent with some
    >> older hardware and we have encoded assumptions that only newer hardware
    >> meets. But I'd guess it's just a plain kvm bug.

    A kvm bug is most likely.

    > It looks like in kvm, before entering the guest, we restore its
    > debug registers:
    > vcpu_enter_guest():
    > if (unlikely(vcpu->arch.switch_db_regs)) {
    > set_debugreg(0, 7);
    > set_debugreg(vcpu->arch.eff_db[0], 0);
    > set_debugreg(vcpu->arch.eff_db[1], 1);
    > set_debugreg(vcpu->arch.eff_db[2], 2);
    > set_debugreg(vcpu->arch.eff_db[3], 3);
    > }
    > But what happens to dr6, I don't know.

    That's done later, in vmx.c:vmx_vcpu_run():

    if (vcpu->arch.switch_db_regs)
    set_debugreg(vcpu->arch.dr6, 6);

    Can you describe the failure? I'll try to construct a test case
    reproducer and work with Jan to fix it.

    error compiling committee.c: too many arguments to function

     \ /
      Last update: 2009-12-20 09:35    [W:0.024 / U:16.068 seconds]
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