linux-kernel - Re: [PATCH v4 3/7] iommu: Support allocation of global PASIDs outside SVA

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Message-ID: <20230417090706.3ac5f858@jacob-builder>
Date:   Mon, 17 Apr 2023 09:07:06 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     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>,
        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>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v4 3/7] iommu: Support allocation of global PASIDs
 outside SVA

Hi Kevin,

On Tue, 11 Apr 2023 08:02:55 +0000, "Tian, Kevin" <kevin.tian@...el.com>
wrote:

> > From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> > Sent: Saturday, April 8, 2023 2:06 AM
> > @@ -28,8 +26,8 @@ static int iommu_sva_alloc_pasid(struct mm_struct
> > *mm, ioasid_t min, ioasid_t ma
> >  		goto out;
> >  	}
> > 
> > -	ret = ida_alloc_range(&iommu_global_pasid_ida, min, max,
> > GFP_KERNEL);
> > -	if (ret < min)
> > +	ret = iommu_alloc_global_pasid(min, max);  
> 
> I wonder whether this can take a device pointer so dev->iommu->max_pasids
> is enforced inside the alloc function.
> 
> and do we even need the min/max parameters? With special pasids reserved
> then what driver needs is just to get a free pasid from the global space
> within dev->iommu->max_pasids constraint...
> 
> iommu_sva_alloc_pasid() can be reworked to avoid min/max by taking a 
> device pointer too.
I think that will work too albeit a philosophical change. It probably
should be called iommu_alloc_dev_global_pasid(dev).

But I feel the current approach is more flexible in that device drivers
can control the range if for some reason it does not want go max_pasid.


Thanks,

Jacob