linux-kernel - RE: [PATCH v5 2/7] iommu/sva: Explicitly exclude RID

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Date:   Fri, 28 Apr 2023 09:40:12 +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>,
        Robin Murphy <robin.murphy@....com>,
        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:     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>,
        "Ranganathan, Narayan" <narayan.ranganathan@...el.com>
Subject: RE: [PATCH v5 2/7] iommu/sva: Explicitly exclude RID_PASID from SVA

> From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Sent: Friday, April 28, 2023 1:50 AM
> 
> SVA PASID allocation is hardcoded to start from 1 because 0 is used for
> RID_PASID, let's make it explicit to avoid the potential conflicts.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> ---
>  drivers/iommu/iommu-sva.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> index c434b95dc8eb..ac7c93bacb5c 100644
> --- a/drivers/iommu/iommu-sva.c
> +++ b/drivers/iommu/iommu-sva.c
> @@ -66,7 +66,7 @@ struct iommu_sva *iommu_sva_bind_device(struct
> device *dev, struct mm_struct *mm
>  		return ERR_PTR(-EOPNOTSUPP);
> 
>  	/* Allocate mm->pasid if necessary. */
> -	ret = iommu_sva_alloc_pasid(mm, 1, max_pasids - 1);
> +	ret = iommu_sva_alloc_pasid(mm, IOMMU_DEF_RID_PASID + 1,
> max_pasids - 1);

To be future proof it's probably cleaner to define a
IOMMU_MAX_RSVD_PASID in case there may be more reserved
pasids in future usages?