linux-kernel - RE: [PATCH v2 17/19] iommu/arm-smmu-v3: Add arm_smmu_viommu_cache

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Message-ID: <BL1PR11MB52712F4AAF7D1388A080A49E8C9B2@BL1PR11MB5271.namprd11.prod.outlook.com>
Date: Wed, 11 Sep 2024 06:25:16 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Jason Gunthorpe <jgg@...dia.com>, Nicolin Chen <nicolinc@...dia.com>
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	<smostafa@...gle.com>, "Liu, Yi L" <yi.l.liu@...el.com>
Subject: RE: [PATCH v2 17/19] iommu/arm-smmu-v3: Add
 arm_smmu_viommu_cache_invalidate

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Friday, September 6, 2024 2:22 AM
> 
> On Thu, Sep 05, 2024 at 11:00:49AM -0700, Nicolin Chen wrote:
> > On Thu, Sep 05, 2024 at 01:20:39PM -0300, Jason Gunthorpe wrote:
> > > On Tue, Aug 27, 2024 at 09:59:54AM -0700, Nicolin Chen wrote:
> > >
> > > > +static int arm_smmu_viommu_cache_invalidate(struct
> iommufd_viommu *viommu,
> > > > +					    struct iommu_user_data_array
> *array)
> > > > +{
> > > > +	struct iommu_domain *domain =
> iommufd_viommu_to_parent_domain(viommu);
> > > > +
> > > > +	return __arm_smmu_cache_invalidate_user(
> > > > +			to_smmu_domain(domain), viommu, array);
> > >
> > > I'd like to have the viommu struct directly hold the VMID. The nested
> > > parent should be sharable between multiple viommus, it doesn't make
> > > any sense that it would hold the vmid.
> > >
> > > This is struggling because it is trying too hard to not have the
> > > driver allocate the viommu, and I think we should just go ahead and do
> > > that. Store the vmid, today copied from the nesting parent in the vmid
> > > private struct. No need for iommufd_viommu_to_parent_domain(), just
> > > rework the APIs to pass the vmid down not a domain.
> >
> > OK. When I designed all this stuff, we still haven't made mind
> > about sharing the s2 domain, i.e. moving the VMID, which might
> > need a couple of more patches to achieve.
> 
> Yes, many more patches, and don't try to do it now.. But we can copy
> the vmid from the s2 and place it in the viommu struct during
> allocation time.
> 

does it assume that a viommu object cannot span multiple physical
IOMMUs so there is only one vmid per viommu?