linux-kernel - Re: [PATCH v2 09/19] iommu/vt-d: Enlightened PASID allocation

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Message-ID: <c847182b-6e5c-5344-a162-29e273a489fb@redhat.com>
Date:   Thu, 25 Apr 2019 09:40:31 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        "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>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>
Cc:     "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 09/19] iommu/vt-d: Enlightened PASID allocation

Hi Liu,

On 4/25/19 9:12 AM, Liu, Yi L wrote:
> Hi Eric,
> 
>> From: Auger Eric [mailto:eric.auger@...hat.com]
>> Sent: Thursday, April 25, 2019 1:28 AM
>> To: Jacob Pan <jacob.jun.pan@...ux.intel.com>; iommu@...ts.linux-foundation.org;
>> Subject: Re: [PATCH v2 09/19] iommu/vt-d: Enlightened PASID allocation
>>
>> Hi Jacob,
>>
>> On 4/24/19 1:31 AM, Jacob Pan wrote:
>>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>>>
>>> If Intel IOMMU runs in caching mode, a.k.a. virtual IOMMU, the IOMMU
>>> driver should rely on the emulation software to allocate and free
>>> PASID IDs.
>> Do we make the decision depending on the CM or depending on the VCCAP_REG?
>>
>> VCCAP_REG description says:
>>
>> If Set, software must use Virtual Command Register interface to allocate and free
>> PASIDs.
> 
> The answer is it depends on the ECAP.VCS and then the PASID allocation bit in
> VCCAP_REG. But VCS bit implies the iommu is a software implementation
> (vIOMMU) of vt-d architecture. Pls refer to the descriptions of "Virtual
> Command Support" in vt-d 3.0 spec.
> 
> "Hardware implementations of this architecture report a value of 0
> in this field. Software implementations (emulation) of this
> architecture may report VCS=1."

OK I understand. But strictly speaking a vIOMMU may not implement CM.
But that's nitpicking ;-)

Thanks

Eric
> 
> Thanks,
> Yi Liu
>