> Am 30.06.2014 um 22:25 schrieb Scott Wood <scottwood@xxxxxxxxxxxxx>:
>
>> On Sun, 2014-06-29 at 23:38 -0500, Bhushan Bharat-R65777 wrote:
>>
>>> -----Original Message-----
>>> From: Wood Scott-B07421
>>> Sent: Friday, June 27, 2014 11:53 PM
>>> To: Bhushan Bharat-R65777
>>> Cc: agraf@xxxxxxx; kvm-ppc@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx
>>> Subject: Re: [PATCH 2/2] KVM : powerpc/booke: Allow debug interrupt injection to
>>> guest
>>>
>>>> On Fri, 2014-06-27 at 11:55 +0530, Bharat Bhushan wrote:
>>>> - /* Force enable debug interrupts when user space wants to debug */
>>>> - if (vcpu->guest_debug) {
>>>> + /*
>>>> + * Force enable debug interrupts when user space wants to debug
>>>> + * and there is no debug interrupt pending for guest to handle.
>>>> + */
>>>> + if (vcpu->guest_debug && !kvmppc_core_pending_debug(vcpu)) {
>>>
>>> Are you trying to allow the guest to be simultaneously debugged by itself and by
>>> host userspace? How does this work?
>>
>> Not actually, Currently we are not partitioning debug resources between
>> host userspace and guest. In fact we do not emulate debug registers for
>> guest. But we want host userspace to pass the interrupt to guest if it
>> is not able to handle.
>
> I don't understand the logic here. A debug interrupt should be injected
> when the programming model in the guest says that a debug interrupt
> should happen. How can that occur currently? If the guest didn't set
> up the debug registers and QEMU still can't handle the debug interrupt,
> that's a bug in QEMU (or KVM, or the hardware...). Injecting the
> interrupt into the guest just adds another bug on top of that.
I don't think QEMU should be aware of these limitations.
>
>>>> #ifdef CONFIG_KVM_BOOKE_HV
>>>> /*
>>>> * Since there is no shadow MSR, sync MSR_DE into the guest @@
>>>> -264,6 +272,16 @@ static void kvmppc_core_dequeue_watchdog(struct kvm_vcpu
>>> *vcpu)
>>>> clear_bit(BOOKE_IRQPRIO_WATCHDOG, &vcpu->arch.pending_exceptions);
>>>> }
>>>>
>>>> +static void kvmppc_core_queue_debug(struct kvm_vcpu *vcpu) {
>>>> + kvmppc_booke_queue_irqprio(vcpu, BOOKE_IRQPRIO_DEBUG); }
>>>> +
>>>> +static void kvmppc_core_dequeue_debug(struct kvm_vcpu *vcpu) {
>>>> + clear_bit(BOOKE_IRQPRIO_DEBUG, &vcpu->arch.pending_exceptions); }
>>>
>>> Is there currently no support for a guest debugging itself (i.e.
>>> guest_debug unset) on e500v2?
>>
>> Yes, It is not yet supported (IACx/DACx/DBCR/DBSR/DSRRx are not yet emulated).
>
> How is it useful to inject a debug exception into the guest, until these
> things are emulated?
We don't have to touch QEMU later then ;). But I agree that it would make a lot of sense to enable guest debugging along the way - it can't be that hard, no?
>
>>>> @@ static int set_sregs_base(struct kvm_vcpu *vcpu,
>>>> if (sregs->u.e.update_special & KVM_SREGS_E_UPDATE_TSR)
>>>> kvmppc_set_tsr(vcpu, sregs->u.e.tsr);
>>>>
>>>> + if (sregs->u.e.update_special & KVM_SREGS_E_UPDATE_DBSR) {
>>>> + vcpu->arch.dbsr = sregs->u.e.dbsr;
>>>> + if (vcpu->arch.dbsr)
>>>> + kvmppc_core_queue_debug(vcpu);
>>>> + else
>>>> + kvmppc_core_dequeue_debug(vcpu);
>>>> + }
>>>> +
>>>> return 0;
>>>> }
>>>
>>> one reg?
>>
>> We are using SREGS but if required we can use one_reg.
>
> I thought we were preferring one reg over sregs for new functionality.
I'm personally torn on this one. The problem here is that the sregs fields and values are already reserved. For anything we don't have an API for yet, yes, one_reg only. IIUC we have the API here, but were lacking the implementation.
Alex
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