linux-kernel - RE: [PATCH v2 2/3] iommu/sva: Stop using ioasid

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Message-ID: <BN9PR11MB527670F77FADCB351E41F8B78CA39@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Wed, 15 Feb 2023 03:24:18 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Jason Gunthorpe <jgg@...dia.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "Jean-Philippe Brucker" <jean-philippe@...aro.com>
CC:     Robin Murphy <robin.murphy@....com>, Will Deacon <will@...nel.org>,
        "David Woodhouse" <dwmw2@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>
Subject: RE: [PATCH v2 2/3] iommu/sva: Stop using ioasid_set for SVA

> From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Sent: Tuesday, February 14, 2023 2:44 PM
> 
> From: Jason Gunthorpe <jgg@...dia.com>
> 
> Instead SVA drivers can use a simple global IDA to allocate PASIDs for
> each mm_struct.
> 
> Future work would be to allow drivers using the SVA APIs to reserve global
> PASIDs from this IDA for their internal use, eg with the DMA API PASID
> support.

I think DMA API PASID will need new API around this IDA. SVA APIs should
be just for SVA.

> +void mm_pasid_drop(struct mm_struct *mm)
>  {
> -	return mmget_not_zero(mm);
> -}
> +	pr_alert("%s %d", __func__, mm->pasid);
> +	if (likely(!pasid_valid(mm->pasid)))
> +		return;
> 
> -/**
> - * iommu_sva_find() - Find mm associated to the given PASID
> - * @pasid: Process Address Space ID assigned to the mm
> - *
> - * On success a reference to the mm is taken, and must be released with
> mmput().
> - *
> - * Returns the mm corresponding to this PASID, or an error if not found.
> - */
> -struct mm_struct *iommu_sva_find(ioasid_t pasid)
> -{
> -	return ioasid_find(&iommu_sva_pasid, pasid, __mmget_not_zero);
> +	ida_free(&iommu_global_pasid_ida, mm->pasid);
>  }

when moving this function following line is missed:

	mm->pasid = INVALID_IOASID;

btw the current placement looks asymmetric. We now have
mm_pasid_init() and mm_pasid_set() in mm.h while mm_pasid_drop()
in iommu-sva.c.

Is it cleaner to introduce a iommu_sva_free_pasid() helper and then
call it from mm_pasid_drop() in mm.h?