Messages in this thread | | | Date | Mon, 2 Nov 2009 14:04:40 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 4/6] hw-breakpoints: Rewrite the hw-breakpoints layer on top of perf events |
| |
On Mon, Nov 02, 2009 at 08:45:56AM +0100, Jan Kiszka wrote: > Frederic Weisbecker wrote: > > On Sun, Nov 01, 2009 at 11:09:03PM +0100, Jan Kiszka wrote: > >>> @@ -3643,14 +3644,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) > >>> trace_kvm_entry(vcpu->vcpu_id); > >>> kvm_x86_ops->run(vcpu, kvm_run); > >>> > >>> - if (unlikely(vcpu->arch.switch_db_regs || test_thread_flag(TIF_DEBUG))) { > >>> - set_debugreg(current->thread.debugreg[0], 0); > >>> - set_debugreg(current->thread.debugreg[1], 1); > >>> - set_debugreg(current->thread.debugreg[2], 2); > >>> - set_debugreg(current->thread.debugreg[3], 3); > >>> - set_debugreg(current->thread.debugreg6, 6); > >>> - set_debugreg(current->thread.debugreg7, 7); > >>> - } > >>> + if (unlikely(vcpu->arch.switch_db_regs || test_thread_flag(TIF_DEBUG))) > >>> + hw_breakpoint_restore(); > >> TIF_DEBUG is only set on active ptrace hw-breakpoints, thus we miss > >> other types here, right? (Note: arch.switch_db_regs is guest-related, > >> thus does not help in this regard.) > >> > >> Jan > >> > > > > > > About this. vcpu->arch.switch_db_regs is guest related but it looks > > like the only thing I need to check. > > > > I'm not sure when it is activated. Is it always done once the guest > > changes its debug registers? I suspect there is a corner case. > > It's set when we had to write to some debugreg[0..4], either for use by > the guest itself or for debugging it from the host. It used to be the > only condition for switching on exit as we saved the registers on entry > (under the same condition). This was reworked recently to avoid the > entry saving. > > > > > Because since I can't anymore assume TIF_DEBUG covers every > > breakpoints uses, it means I'll need to maintain a refcount of > > breakpoints in use. > > Well, I have one already, but it is splitted into several refcounts > > (per task events, per cpu, non-pinned, etc...). And since > > vcpu_enter_guest() is a fast path, I'll need to maintain another global > > per cpu one, without lock or further operations to know if we need > > to save the debug registers, just a simple check. > > > > I'm not 100% sure right now if we still need "switch_db_reg" in case we > have a reliable indicator that the host requires properly set registers. > ATM I would dare to say, we don't, but I need to think about this again. > > Jan >
Ok. I'm going to just check if the host has active breakpoints pending and if so, I'll restore them while exiting the guest.
Thanks.
| |