Re: [PATCH v6 13/14] iommu/arm-smmu-v3: Report events that belong to devices attached to vIOMMU

[Nicolin Chen <nicolinc@nvidia.com>]

On Tue, Feb 18, 2025 at 02:50:46PM -0400, Jason Gunthorpe wrote:
> On Tue, Feb 18, 2025 at 10:28:04AM -0800, Nicolin Chen wrote:
> > On Tue, Feb 18, 2025 at 01:18:21PM -0400, Jason Gunthorpe wrote:
> > > On Fri, Jan 24, 2025 at 04:30:42PM -0800, Nicolin Chen wrote:
> > > 
> > > > @@ -1831,31 +1831,30 @@ static int arm_smmu_handle_event(struct arm_smmu_device *smmu,
> > > >  		return -EOPNOTSUPP;
> > > >  	}
> > > 
> > > There is still the filter at the top:
> > > 
> > > 	switch (event->id) {
> > > 	case EVT_ID_TRANSLATION_FAULT:
> > > 	case EVT_ID_ADDR_SIZE_FAULT:
> > > 	case EVT_ID_ACCESS_FAULT:
> > > 	case EVT_ID_PERMISSION_FAULT:
> > > 		break;
> > > 	default:
> > > 		return -EOPNOTSUPP;
> > > 	}
> > > 
> > > Is that right here or should more event types be forwarded to the
> > > guest?
> > 
> > That doesn't seem to be right. Something like EVT_ID_BAD_CD_CONFIG
> > should be forwarded too. I will go through the list.
> 
> I think the above should decode into a 'faultable' path because they
> all decode to something with an IOVA
> 
> The rest should decode to things that include a SID and the SID decode
> should always be forwarded to the VM. Maybe there are small
> exclusions, but generally that is how I would see it..

Ack. SMMU spec defines three type:
"Three categories of events might be recorded into the Event queue:
 • Configuration errors.
 • Faults from the translation process.
 • Miscellaneous."

The driver cares the first two only, as you remarked here.

> > > This already holds the streams_mutex across all of this, do you think
> > > we should get rid of the vmaster_rwsem and hold the streams_mutex on
> > > write instead?
> > 
> > They are per master v.s. per smmu. The latter one would make master
> > commits/attaches exclusive, which feels unnecessary to me, although
> > it would make the code here slightly cleaner..
> 
> I'd pay the cost on the attach side to have a single lock on the fault
> side..

OK. Maybe a small patch to turn the streams_mutex to streams_rwsem?

Thanks
Nicolin