> -----Original Message-----
> From: Nicolin Chen <[email protected]>
> Sent: 30 December 2025 18:22
> To: Shameer Kolothum <[email protected]>
> Cc: [email protected]; [email protected];
> [email protected]; [email protected]; Nathan Chen
> <[email protected]>; Matt Ochs <[email protected]>; Jason Gunthorpe
> <[email protected]>; [email protected];
> [email protected]; [email protected]; Krishnakant Jaju
> <[email protected]>
> Subject: Re: [RFC PATCH 10/16] hw/arm/tegra241-cmdqv: Allocate vEVENTQ
> object
>
> 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.
Ok. That is reassuring then. I will add that as a comment and move it.
> > > > 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.
I think, generally it is a last resort option and should be avoided.
Thanks,
Shameer
