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

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Message-ID: <20230417094629.59fcfde6@jacob-builder>
Date:   Mon, 17 Apr 2023 09:46:29 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.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>,
        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 Baolu,

On Wed, 12 Apr 2023 09:37:48 +0800, Baolu Lu <baolu.lu@...ux.intel.com>
wrote:

> On 4/11/23 4:02 PM, Tian, Kevin 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.  
> 
> Agreed. Instead of using the open code, it looks better to have a helper
> like dev_iommu_max_pasids().
yes, probably export dev_iommu_get_max_pasids(dev)?

But if I understood Kevin correctly, he's also suggesting that the
interface should be changed to iommu_alloc_global_pasid(dev), my concern is
that how do we use this function to reserve RID_PASID which is not specific
to a device?

> 
> > 
> > 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.  
> 
> Best regards,
> baolu


Thanks,

Jacob