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

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Message-ID: <5882ee52-9657-250d-0474-13edffa7b6b9@linux.intel.com>
Date:   Wed, 12 Apr 2023 09:37:48 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        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>,
        Joerg Roedel <joro@...tes.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>
Cc:     baolu.lu@...ux.intel.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 v4 3/7] iommu: Support allocation of global PASIDs outside
 SVA

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().

> 
> 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