On Tue, Dec 30, 2025 at 10:10:48AM -0800, Shameer Kolothum wrote:
> > > > On Wed, Dec 10, 2025 at 01:37:31PM +0000, Shameer Kolothum wrote:
> > > > > @@ -259,11 +305,16 @@ static bool
> > > > tegra241_cmdqv_setup_vcmdq(Tegra241CMDQV *cmdqv, int index,
> > > > > g_free(vcmdq);
> > > > > }
> > > > >
> > > > > + if (!tegra241_cmdqv_alloc_veventq(cmdqv, errp)) {
> > > > > + return false;
> > > > > + }
> > > > > +
> > > >
> > > > I think this should be called in tegra241_cmdqv_alloc_viommu().
> > >
> > > Should/Can we? _alloc_viommu() will happen before the Guest boot.
> >
> > I think we can. vEVENTQ only needs vIOMMU ID. It's per VINTF v.s.
> > per VCMDQ (HW_QUEUE). So, it should follow vIOMMU.
> >
> > Basically, we can allocate vIOMMU (VINTF) and its vEVENTQ even if
> > the VINTF doesn't contain any LVCMDQs, which are allocated/mapped
> > to the VINTF later via HW_QUEUE allocations.
>
> But what happens when you receive an event from host during that time?
> Should we just ignore it? Or is that not possible at all from a hoist driver
> perspective? To me, it looks like the natural flow is setup vEVENTQ when
> Guest is ready to receive the events.
I don't think that will happen. The IRQ register for VINTF/vIOMMU
is LVCMDQ_ERR_MAP. If there is no HW_QUEUE allocated to the VINTF,
there shouldn't be a vEVENT. Otherwise, it would be a kernel bug,
IMHO.
> > > Unlike the SMMUv3 vEVENTQ for accel case, we restrict the hotplug
> > > use case when the tegra214-cmdqv is set. And as soon as Guest setup
> > vCMDQ
> > > the vEVENTQ is enabled here. Do you see any issues with this approach?
> >
> > Once guest OS is booting, !tegra241_cmdqv_alloc_veventq will fail
> > tegra241_cmdqv_setup_vcmdq while it cannot break the guest OS any
> > more. Then, the whole thing wouldn't work although guest OS runs?
>
> If vEVENTQ is mandatory we could exit the Guest with a proper msg in
> case tegra241_cmdqv_alloc_veventq() fails, right?
I don't know. But that doesn't sound right to me. In my mind, once
the guest OS is booting, it could only stop with something like a
blue screen..
Maybe QEMU experts can shed some light here.
Nicolin
