On 09/01/2009 01:42 PM, Jan Kiszka wrote:
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 891234b..9e3acbd 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3627,14 +3627,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) kvm_guest_enter(); - get_debugreg(vcpu->arch.host_dr6, 6); - get_debugreg(vcpu->arch.host_dr7, 7); if (unlikely(vcpu->arch.switch_db_regs)) { - get_debugreg(vcpu->arch.host_db[0], 0); - get_debugreg(vcpu->arch.host_db[1], 1); - get_debugreg(vcpu->arch.host_db[2], 2); - get_debugreg(vcpu->arch.host_db[3], 3); -I'm fine with this for the common case, but we should switch to the safe pattern on test_thread_flag(TIF_DEBUG), ie. if someone debugs qemu using hardware break/watchpoints.
IIUC, thread.debugregs should be synced with the hardware registers. The kernel itself only writes to the debug registers, so we're safe doing the same.
set_debugreg(0, 7); set_debugreg(vcpu->arch.eff_db[0], 0); set_debugreg(vcpu->arch.eff_db[1], 1); @@ -3645,15 +3638,14 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) trace_kvm_entry(vcpu->vcpu_id); kvm_x86_ops->run(vcpu); - if (unlikely(vcpu->arch.switch_db_regs)) { - set_debugreg(0, 7); - set_debugreg(vcpu->arch.host_db[0], 0); - set_debugreg(vcpu->arch.host_db[1], 1); - set_debugreg(vcpu->arch.host_db[2], 2); - set_debugreg(vcpu->arch.host_db[3], 3); + if (unlikely(vcpu->arch.switch_db_regs || test_thread_flag(TIF_DEBUG))) {IIRC, you must clear dr7 before loading dr0..3 to avoid spurious effects.
Yeah, I thought of it but forgot to implement it.
+ set_debugreg(current->thread.debugreg0, 0); + set_debugreg(current->thread.debugreg1, 1); + set_debugreg(current->thread.debugreg2, 2); + set_debugreg(current->thread.debugreg3, 3); + set_debugreg(current->thread.debugreg6, 6); + set_debugreg(current->thread.debugreg7, 7); } - set_debugreg(vcpu->arch.host_dr6, 6); - set_debugreg(vcpu->arch.host_dr7, 7);Unless I miss something ATM, moving this into the if-clause should cause troubles if the guest leaves dr7 armed behind. But I need to refresh my memory on this.
The hardware will clear dr7 on exit. Updated patch to follow. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
