linux-kernel - RE: [PATCH v4 01/17] iommu: Add hwpt_type with user_data for domain_alloc

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Date:   Wed, 27 Sep 2023 01:08:01 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     Robin Murphy <robin.murphy@....com>,
        Baolu Lu <baolu.lu@...ux.intel.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Duan, Zhenzhong" <zhenzhong.duan@...el.com>,
        "Martins, Joao" <joao.m.martins@...cle.com>
Subject: RE: [PATCH v4 01/17] iommu: Add hwpt_type with user_data for
 domain_alloc_user op

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Wednesday, September 27, 2023 12:29 AM
> 
> On Tue, Sep 26, 2023 at 06:37:55AM +0000, Tian, Kevin wrote:
> > > From: Robin Murphy <robin.murphy@....com>
> > > Sent: Friday, September 22, 2023 5:48 PM
> > >
> > > I could go on enjoying myself, but basically yeah, "default" can't be a
> > > type in itself (at best it would be a meta-type which could be
> > > requested, such that it resolves to some real type to actually
> > > allocate), so a good name should reflect what the type functionally
> > > *means* to the user. IIUC the important distinction is that it's an
> > > abstract kernel-owned pagetable for the user to indirectly control via
> > > the API, rather than one it owns and writes directly (and thus has to be
> > > in a specific agreed format).
> > >
> >
> > IOMMU_HWPT_TYPE_KERNEL then?
> >
> > IOMMU_HWPT_TYPE_GENERIC also doesn't sound a straight word.
> 
> At the end of the day this enum is the type tag for:
> 
>  struct iommu_hwpt_alloc {
>  	__u32 size;
>  	__u32 pt_id;
>  	__u32 out_hwpt_id;
>  	__u32 __reserved;
> +	__u32 hwpt_type;
> +	__u32 data_len;
> +	__aligned_u64 data_uptr;
>  };
> 
> That pointer.
> 
> IOMMU_HWPT_ALLOC_DATA_NONE = 0
> IOMMU_HWPT_ALLOC_DATA_INTEL_VTD
> IOMMU_HWPT_ALLOC_DATA_ARM_SMMUV3
> 
> etc?
> 
> DATA_NONE requires data_len == 0
> 

Looks good. Probably hwpt_type can be also renamed to data_type
to better match this interpretation.