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: <Z7TRNL0u0YmN30ax@nvidia.com>
Date: Tue, 18 Feb 2025 10:28:04 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...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 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.

> >  	mutex_lock(&smmu->streams_mutex);
> [..]
>   
> > -	ret = iommu_report_device_fault(master->dev, &fault_evt);
> > +	if (event->stall) {
> > +		ret = iommu_report_device_fault(master->dev, &fault_evt);
> > +	} else {
> > +		down_read(&master->vmaster_rwsem);
> 
> 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..

Thanks
Nicolin