linux-kernel - RE: [PATCH v2 3/8] iommu/sva: Support reservation of global SVA PASIDs

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Message-ID: <BN9PR11MB527652D88D15437F52FCE8268C889@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Tue, 28 Mar 2023 07:35:43 +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>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>
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>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>
Subject: RE: [PATCH v2 3/8] iommu/sva: Support reservation of global SVA
 PASIDs

> From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Sent: Tuesday, March 28, 2023 7:22 AM
> 
> +/**
> + * @brief
> + *	Reserve a PASID from the SVA global number space.
> + *
> + * @param min starting range, inclusive
> + * @param max ending range, inclusive
> + * @return The reserved PASID on success or IOMMU_PASID_INVALID on
> failure.
> + */
> +ioasid_t iommu_sva_reserve_pasid(ioasid_t min, ioasid_t max)
> +{
> +	int ret;
> +
> +	if (!pasid_valid(min) || !pasid_valid(max) ||
> +	    min == 0 || max < min)
> +		return IOMMU_PASID_INVALID;
> +
> +	ret = ida_alloc_range(&iommu_global_pasid_ida, min, max,
> GFP_KERNEL);
> +	if (ret < 0)
> +		return IOMMU_PASID_INVALID;
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_sva_reserve_pasid);
> +

Look at this function. There is no single word about sva except
in the function name.

sva is just one user of global pasids.

when a driver supports sva it has to always use global pasids even
for non-sva usages like dma pasid.

but this doesn't mean that we should build the API around sva.

it's really about global pasids.

let's just call it clearly as iommu_alloc_global_pasid(min, max).

Then we can define a wrapper iommu_reserve_global_pasid(pasid)
as iommu_alloc_global_pasid(pasid, pasid).

for PASID#0 driver calls iommu_reserve_global_pasid(0).

for dma pasid driver calls iommu_alloc_global_pasid() to get a random
one instead of reserving pasid#1.

this would be future proof when the same driver starts to allocate
more pasids for other usages e..g siov.