Re: [PATCH v7 13/14] iommu/arm-smmu-v3: Report events that belong to devices attached to vIOMMU

Pranjal Shrivastava
2025-02-25T16:47:58Z

On Mon, Feb 24, 2025 at 01:56:46PM -0800, Nicolin Chen wrote:
> On Mon, Feb 24, 2025 at 09:35:14PM +0000, Pranjal Shrivastava wrote:
> > On Sat, Feb 22, 2025 at 07:54:10AM -0800, Nicolin Chen wrote:
> > > +int arm_vmaster_report_event(struct arm_smmu_vmaster *vmaster, u64 *evt)
> > > +{
> > > + struct iommu_vevent_arm_smmuv3 vevt;
> > > + int i;
> > > +
> > > + lockdep_assert_held(&vmaster->vsmmu->smmu->streams_mutex);
> > > +
> > > + vevt.evt[0] = cpu_to_le64((evt[0] & ~EVTQ_0_SID) |
> > > + FIELD_PREP(EVTQ_0_SID, vmaster->vsid));
> > > + for (i = 1; i < EVTQ_ENT_DWORDS; i++)
> > > + vevt.evt[i] = cpu_to_le64(evt[i]);
> >
> > Just thinking out loud here:
> > I understand the goal here is to "emulate" an IOMMU. But I'm just
> > wondering if we could report struct events instead of the raw event?
> >
> > For example, can't we have something like arm_smmu_event here with the
> > sid changed to vsid?
> >
> > Are we taking the raw event since we want to keep the `u64 event_data[]`
> > field within `struct iommufd_vevent` generic to all architectures?
>
> The ABIs for vSMMU are defined in the HW languange, e.g. cmd, ste.
> Thus, here evt in raw too.
>

Ack. Makes sense.

> > > - ret = iommu_report_device_fault(master->dev, &fault_evt);
> > > + if (event->stall) {
> > > + ret = iommu_report_device_fault(master->dev, &fault_evt);
> > > + } else {
> > > + if (master->vmaster && !event->s2)
> > > + ret = arm_vmaster_report_event(master->vmaster, evt);
> > > + else
> > > + ret = -EFAULT; /* Unhandled events should be pinned */
> > > + }
> >
> > Nit:
> > I don't see the `arm_smmu_handle_event` being called elsewhere, is there
> > a reason to return -EFAULT instead of -EOPNOTSUPP here?
> >
> > I think the current behavior here is to return -EOPNOTSUPP if (!event->stall).
> > Whereas, what we're doing here is:
> > if (event->stall) {
> > ...
> > /* do legacy stuff */
> > ...
> > }
> >
> > else {
> > if (master->vmaster && !event->s2)
> > arm_vmaster_report_event(vmaster, evt);
> > else
> > ret = -EFAULT
> > }
> >
> > mutex_unlock(&smmu->streams_mutex);
> > return ret;
> >
> > Thus, we end up returning -EFAULT instead of -EOPNOTSUPP in case
> > event->stall == false. I agree that we aren't really checking the return
> > value in the evtq_thread handler, but I'm wondering if we should ensure
> > that we end up retaining the same behaviour as we have right now?
>
> Oh, it looks like -EOPNOTSUPP should be returned here. Will fix.
>

With the fix to return `-EOPNOTSUPP`:

Reviewed-by: Pranjal Shrivastava <praan@google.com>

Thanks,
Praan