linux-kernel - Re: [PATCH v6 01/10] iommu/vt-d: Enlightened PASID allocation

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Date:   Fri, 25 Oct 2019 09:42:43 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     baolu.lu@...ux.intel.com, "Raj, Ashok" <ashok.raj@...el.com>,
        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>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Eric Auger <eric.auger@...hat.com>
Subject: Re: [PATCH v6 01/10] iommu/vt-d: Enlightened PASID allocation

Hi,

On 10/24/19 5:11 AM, Jacob Pan wrote:
> On Wed, 23 Oct 2019 10:55:23 -0700
> Jacob Pan <jacob.jun.pan@...ux.intel.com> wrote:
> 
>>>> Do you have to check this everytime? every dmar_readq is going to
>>>> trap to the other side ...
>>>
>>> Yes. We don't need to check it every time. Check once and save the
>>> result during boot is enough.
>>>
>>> How about below incremental change?
>>>    
>> Below is good but I was thinking to include vccap in struct
>> intel_iommu{} where cap and ecaps reside. i.e.
>> diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
>> index 14b87ae2916a..e2cf25c9c956 100644
>> --- a/include/linux/intel-iommu.h
>> +++ b/include/linux/intel-iommu.h
>> @@ -528,6 +528,7 @@ struct intel_iommu {
>>          u64             reg_size; /* size of hw register set */
>>          u64             cap;
>>          u64             ecap;
>> +       u64             vccap;
>>
>> Also, we can use a static branch here.
>>
> On a second thought, we cannot use static(branch) here in that we
> cannot assume there is only one vIOMMU all the time. Have to cache the
> vccap per iommu.

intel_iommu is a per iommu structure, right? Or I missed anything?

> 
>>> diff --git a/drivers/iommu/intel-pasid.c
>>> b/drivers/iommu/intel-pasid.c index ff7e877b7a4d..c15d9d7e1e73
>>> 100644 --- a/drivers/iommu/intel-pasid.c
>>> +++ b/drivers/iommu/intel-pasid.c
>>> @@ -29,22 +29,29 @@ u32 intel_pasid_max_id = PASID_MAX;
>>>
> [Jacob Pan]
> 

Best regards,
baolu