linux-kernel - RE: [PATCH v5 3/7] iommu: Move global PASID allocation from SVA to core

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Message-ID: <BN9PR11MB5276C41CCCCF3FDEA7DDF7AC8C6B9@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Fri, 28 Apr 2023 09:46:25 +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 3/7] iommu: Move global PASID allocation from SVA to
 core

> From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Sent: Friday, April 28, 2023 1:50 AM
> 
> Devices that use Intel ENQCMD to submit work must use global PASIDs in
> that the PASID are stored in a per CPU MSR. When such device need to
> submit work for in-kernel DMA with PASID, it must allocate PASIDs from
> the same global number space to avoid conflict.

well the device itself cannot submit work to itself. It's software to
submit work to the device. 😊

>  /* Allocate a PASID for the mm within range (inclusive) */
> -static int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min,
> ioasid_t max)
> +static int iommu_sva_alloc_pasid(struct mm_struct *mm, struct device *dev)
>  {
>  	int ret = 0;
> 
> -	if (!pasid_valid(min) || !pasid_valid(max) ||
> -	    min == 0 || max < min)
> -		return -EINVAL;
> -
>  	mutex_lock(&iommu_sva_lock);
>  	/* Is a PASID already associated with this mm? */
> -	if (pasid_valid(mm->pasid)) {
> -		if (mm->pasid < min || mm->pasid > max)
> -			ret = -EOVERFLOW;
> +	if (pasid_valid(mm->pasid))
>  		goto out;

emmm here you still want to check whether mm->pasid exceeds
the max pasid width of the bound device.