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

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Message-ID: <20250218185046.GK4099685@nvidia.com>
Date: Tue, 18 Feb 2025 14:50:46 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: kevin.tian@...el.com, corbet@....net, will@...nel.org, joro@...tes.org,
	suravee.suthikulpanit@....com, robin.murphy@....com,
	dwmw2@...radead.org, baolu.lu@...ux.intel.com, shuah@...nel.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org,
	eric.auger@...hat.com, jean-philippe@...aro.org, mdf@...nel.org,
	mshavit@...gle.com, shameerali.kolothum.thodi@...wei.com,
	smostafa@...gle.com, ddutile@...hat.com, yi.l.liu@...el.com,
	patches@...ts.linux.dev
Subject: Re: [PATCH v6 13/14] iommu/arm-smmu-v3: Report events that belong to
 devices attached to vIOMMU

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..

> > 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..

Jason