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

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Message-ID: <A2975661238FB949B60364EF0F2C257439E840F5@SHSMSX104.ccr.corp.intel.com>
Date:   Thu, 25 Apr 2019 07:12:02 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Auger Eric <eric.auger@...hat.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 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."

Thanks,
Yi Liu