linux-kernel - Re: [PATCH v7 01/10] iommu: Add pasids field in struct iommu

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Date:   Wed, 25 May 2022 10:13:20 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Jiang, Dave" <dave.jiang@...el.com>, Vinod Koul <vkoul@...nel.org>
Cc:     baolu.lu@...ux.intel.com, Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [PATCH v7 01/10] iommu: Add pasids field in struct iommu_device

On 2022/5/25 10:03, Baolu Lu wrote:
>>> diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
>>> index 4de960834a1b..1c3cf267934d 100644
>>> --- a/drivers/iommu/intel/dmar.c
>>> +++ b/drivers/iommu/intel/dmar.c
>>> @@ -1126,6 +1126,10 @@ static int alloc_iommu(struct dmar_drhd_unit
>>> *drhd)
>>>
>>>       raw_spin_lock_init(&iommu->register_lock);
>>>
>>> +    /* Supports full 20-bit PASID in scalable mode. */
>>> +    if (ecap_pasid(iommu->ecap))
>>> +        iommu->iommu.pasids = 1UL << 20;
>>> +
>>
>> supported pasid bits is reported by ecap_pss(). I don't think we should
>> assume 20bits here.
> 
> Yes. I overlooked this. Thanks for reminding.
> 
> Another thing I need to improve is that scalable mode could be disabled.
> This field should be 0 in that case.

I will change above to:

+        /*
+         * A value of N in PSS field of eCap register indicates hardware
+         * supports PASID field of N+1 bits.
+         */
+        if (pasid_supported(iommu))
+                iommu->iommu.max_pasids = 2UL << ecap_pss(iommu->ecap);

Best regards,
baolu