On Tue, 2014-07-01 at 08:23 +0200, Alexander Graf wrote:
>
> > 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.
OK, but we should at least have some idea of how the whole thing is
supposed to work, in order to determine if this is the correct behavior
for QEMU. I thought the model was that debug resources are either owned
by QEMU or by the guest, and in the latter case, QEMU would never see
the debug exception to begin with.
> >>> 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.
>From a QEMU perspective, are we going to want to update this at the same
time as everything else, or would jumping through sregs hoops be a
nuisance? Is the long term goal to have one reg support for everything?
-Scott
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