linux-kernel - Re: [PATCH v2 11/19] iommu/vt-d: Replace Intel specific PASID allocator with IOASID

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Message-ID: <7529f2ca-167b-5e65-9330-9093638e9f91@arm.com>
Date:   Mon, 29 Apr 2019 11:00:51 +0100
From:   Jean-Philippe Brucker <jean-philippe.brucker@....com>
To:     Auger Eric <eric.auger@...hat.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Andriy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v2 11/19] iommu/vt-d: Replace Intel specific PASID
 allocator with IOASID

On 27/04/2019 09:38, Auger Eric wrote:
>>>> --- a/drivers/iommu/intel-iommu.c
>>>> +++ b/drivers/iommu/intel-iommu.c
>>>> @@ -5153,7 +5153,7 @@ static void auxiliary_unlink_device(struct
>>>> dmar_domain *domain, domain->auxd_refcnt--;
>>>>  
>>>>  	if (!domain->auxd_refcnt && domain->default_pasid > 0)
>>>> -		intel_pasid_free_id(domain->default_pasid);
>>>> +		ioasid_free(domain->default_pasid);
>>>>  }
>>>>  
>>>>  static int aux_domain_add_dev(struct dmar_domain *domain,
>>>> @@ -5171,9 +5171,8 @@ static int aux_domain_add_dev(struct
>>>> dmar_domain *domain, if (domain->default_pasid <= 0) {
>>>>  		int pasid;
>>>>  
>>>> -		pasid = intel_pasid_alloc_id(domain, PASID_MIN,
>>>> -
>>>> pci_max_pasids(to_pci_dev(dev)),
>>>> -					     GFP_KERNEL);
>>>> +		pasid = ioasid_alloc(NULL, PASID_MIN,
>>>> pci_max_pasids(to_pci_dev(dev)) - 1,
>>>> +				domain);
>>>>  		if (pasid <= 0) {  
>>> ioasid_t is a uint and returns INVALID_IOASID on error. Wouldn't it be
>>> simpler to make ioasid_alloc return an int?
>> Well, I think we still want the full uint range - 1(INVALID_IOASID).
>> Intel uses 20bit but I think SMMUs use 32 bits for streamID? I
>> should just check 
>> 	if (pasid == INVALID_IOASID) {
> Jean-Philippe may correct me but SMMU uses 20b SubstreamId which is a
> superset of PASIDs. StreamId is 32b.

Right, we use 20 bits for PASIDs (== SubstreamID really). Given the
choices that vendors are making for PASIDs (a global namespace rather
than per-VM), I wouldn't be surprised if they extend the size of PASIDs
in a couple of years, so I added the typedef ioasid_t to ease a possible
change from 32-bit to 64 in the future.

Thanks,
Jean