linux-kernel - Re: [PATCH v4 05/12] iommu/vt-d: Reserve a domain id for FL and PT modes

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Message-ID: <855f56ac-80be-8179-ba99-45ef99ccb87f@linux.intel.com>
Date:   Thu, 8 Nov 2018 10:22:14 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>, Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>
Cc:     baolu.lu@...ux.intel.com, "Raj, Ashok" <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "Sun, Yi Y" <yi.y.sun@...el.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: Re: [PATCH v4 05/12] iommu/vt-d: Reserve a domain id for FL and PT
 modes

Hi,

On 11/7/18 2:55 PM, Liu, Yi L wrote:
> Hi Baolu,
> 
>> From: Lu Baolu [mailto:baolu.lu@...ux.intel.com]
>> Sent: Monday, November 5, 2018 1:32 PM
>> Subject: [PATCH v4 05/12] iommu/vt-d: Reserve a domain id for FL and PT modes
>>
>> Vt-d spec rev3.0 (section 6.2.3.1) requires that each pasid
>> entry for first-level or pass-through translation should be
>> programmed with a domain id different from those used for
>> second-level or nested translation. It is recommended that
>> software could use a same domain id for all first-only and
>> pass-through translations.
>>
>> This reserves a domain id for first-level and pass-through
>> translations.
>>
>> Cc: Ashok Raj <ashok.raj@...el.com>
>> Cc: Jacob Pan <jacob.jun.pan@...ux.intel.com>
>> Cc: Kevin Tian <kevin.tian@...el.com>
>> Cc: Liu Yi L <yi.l.liu@...el.com>
>> Cc: Sanjay Kumar <sanjay.k.kumar@...el.com>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> ---
>>   drivers/iommu/intel-iommu.c | 10 ++++++++++
>>   drivers/iommu/intel-pasid.h |  6 ++++++
>>   2 files changed, 16 insertions(+)
>>
>> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
>> index 9331240c70b8..2f7455ee4e7a 100644
>> --- a/drivers/iommu/intel-iommu.c
>> +++ b/drivers/iommu/intel-iommu.c
>> @@ -1618,6 +1618,16 @@ static int iommu_init_domains(struct intel_iommu
>> *iommu)
>>   	 */
>>   	set_bit(0, iommu->domain_ids);
>>
>> +	/*
>> +	 * Vt-d spec rev3.0 (section 6.2.3.1) requires that each pasid
>> +	 * entry for first-level or pass-through translation modes should
>> +	 * be programmed with a domain id different from those used for
>> +	 * second-level or nested translation. We reserve a domain id for
>> +	 * this purpose.
>> +	 */
>> +	if (sm_supported(iommu))
>> +		set_bit(FLPT_DEFAULT_DID, iommu->domain_ids);
> 
> "FLPT_DEFAULT_DID" looks very likely for first level translation. How about
> "PT_FL_DEFAULT_DID"?

We have comments above it, so people won't be confused.

> 
>>   	return 0;
>>   }
>>
>> diff --git a/drivers/iommu/intel-pasid.h b/drivers/iommu/intel-pasid.h
>> index 12f480c2bb8b..03c1612d173c 100644
>> --- a/drivers/iommu/intel-pasid.h
>> +++ b/drivers/iommu/intel-pasid.h
>> @@ -17,6 +17,12 @@
>>   #define PDE_PFN_MASK			PAGE_MASK
>>   #define PASID_PDE_SHIFT			6
>>
>> +/*
>> + * Domain ID reserved for pasid entries programmed for first-level
>> + * only and pass-through transfer modes.
>> + */
>> +#define FLPT_DEFAULT_DID		1
> 
> Would be helpful to elaborate why DID 1 is selected in the patch
> description.

Yeah. DID 0 has been caved out for caching mode and we start from 1 for
this.

Best regards,
Lu Baolu