From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     Jacob Pan <jacob.jun.pan@linux.intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "iommu@lists.linux.dev" <iommu@lists.linux.dev>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        "Jean-Philippe Brucker" <jean-philippe@linaro.com>
CC:     Robin Murphy <robin.murphy@arm.com>, Will Deacon <will@kernel.org>,
        "David Woodhouse" <dwmw2@infradead.org>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>
Subject: RE: [PATCH v2 2/3] iommu/sva: Stop using ioasid_set for SVA
Thread-Topic: [PATCH v2 2/3] iommu/sva: Stop using ioasid_set for SVA
Thread-Index: AQHZQD9F7KUt2c8R1ECOqV7mphNOEq7PV2IA
Date:   Wed, 15 Feb 2023 03:24:18 +0000
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References: <20230214064414.1038058-1-jacob.jun.pan@linux.intel.com>
 <20230214064414.1038058-3-jacob.jun.pan@linux.intel.com>
In-Reply-To: <20230214064414.1038058-3-jacob.jun.pan@linux.intel.com>
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> From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Sent: Tuesday, February 14, 2023 2:44 PM
>=20
> From: Jason Gunthorpe <jgg@nvidia.com>
>=20
> Instead SVA drivers can use a simple global IDA to allocate PASIDs for
> each mm_struct.
>=20
> Future work would be to allow drivers using the SVA APIs to reserve globa=
l
> 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;
>=20
> -/**
> - * 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 =3D 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?