linux-kernel - Re: [PATCH v3 05/11] iommu: Pass in a viommu pointer to domain_alloc

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Message-ID: <20241017173855.GO3559746@nvidia.com>
Date: Thu, 17 Oct 2024 14:38:55 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...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 05/11] iommu: Pass in a viommu pointer to
 domain_alloc_user op

On Thu, Oct 17, 2024 at 10:21:31AM -0700, Nicolin Chen wrote:
> On Thu, Oct 17, 2024 at 01:51:51PM -0300, Jason Gunthorpe wrote:
> > On Wed, Oct 09, 2024 at 09:38:05AM -0700, Nicolin Chen wrote:
> > > With a viommu object wrapping a potentially shareable S2 domain, a nested
> > > domain should be allocated by associating to a viommu instead.
> > > 
> > > For drivers without a viommu support, keep the parent domain input, which
> > > should be just viommu->hwpt->common.domain otherwise.
> > > 
> > > Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> > > ---
> > >  include/linux/iommu.h                       | 1 +
> > >  drivers/iommu/amd/iommu.c                   | 1 +
> > >  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 1 +
> > >  drivers/iommu/intel/iommu.c                 | 1 +
> > >  drivers/iommu/iommufd/hw_pagetable.c        | 5 +++--
> > >  drivers/iommu/iommufd/selftest.c            | 1 +
> > >  6 files changed, 8 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > > index 3a50f57b0861..9105478bdbcd 100644
> > > --- a/include/linux/iommu.h
> > > +++ b/include/linux/iommu.h
> > > @@ -573,6 +573,7 @@ struct iommu_ops {
> > >  	struct iommu_domain *(*domain_alloc)(unsigned iommu_domain_type);
> > >  	struct iommu_domain *(*domain_alloc_user)(
> > >  		struct device *dev, u32 flags, struct iommu_domain *parent,
> > > +		struct iommufd_viommu *viommu,
> > >  		const struct iommu_user_data *user_data);
> > 
> > This re-enforces my feeling we should have made a
> > domain_alloc_nested()..
> 
> That could make these changes slightly cleaner. Maybe adding a
> small series prior to your initial nesting, and get it merged
> quickly?

Maybe we should put an op on the viommu_ops to allocate a nested
domain?

It make some sense and resolves my worries about checking for
driver ownership.

Jason