linux-kernel - Re: [PATCH v3 08/11] iommufd/selftest: Add IOMMU_VIOMMU_TYPE

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Message-ID: <ZxFIjfc7gtXocb/n@Asurada-Nvidia>
Date: Thu, 17 Oct 2024 10:25:33 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: <kevin.tian@...el.com>, <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>,
	<eric.auger@...hat.com>, <jean-philippe@...aro.org>, <mdf@...nel.org>,
	<mshavit@...gle.com>, <shameerali.kolothum.thodi@...wei.com>,
	<smostafa@...gle.com>, <yi.l.liu@...el.com>, <aik@....com>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v3 08/11] iommufd/selftest: Add IOMMU_VIOMMU_TYPE_SELFTEST

On Thu, Oct 17, 2024 at 02:15:00PM -0300, Jason Gunthorpe wrote:
> On Wed, Oct 09, 2024 at 09:38:08AM -0700, Nicolin Chen wrote:
> 
> > +static struct iommufd_viommu *
> > +mock_viommu_alloc(struct iommu_device *iommu_dev, struct iommu_domain *domain,
> > +		  struct iommufd_ctx *ictx, unsigned int viommu_type)
> > +{
> > +	struct mock_iommu_device *mock_iommu =
> > +		container_of(iommu_dev, struct mock_iommu_device, iommu_dev);
> > +	struct mock_viommu *mock_viommu;
> > +
> > +	if (viommu_type != IOMMU_VIOMMU_TYPE_SELFTEST)
> > +		return ERR_PTR(-EOPNOTSUPP);
> 
> What about the default viommu? What happens then?

IOMMU_VIOMMU_TYPE_DEFAULT is allocated by the core, it won't go
down to iommu_ops->viommu_alloc (this function).

> > +	mock_viommu = iommufd_viommu_alloc(ictx, mock_viommu, core,
> > +					   &mock_viommu_ops);
> > +	if (IS_ERR(mock_viommu))
> > +		return ERR_CAST(mock_viommu);
> > +
> > +	if (!refcount_inc_not_zero(&mock_iommu->users)) {
> 
> It would be a bug if the iommu_dev being passed in was somehow
> released while iommufd had hold of it through vfio. So just use
> refcount_inc()

OK.

Thanks
Nicolin