linux-kernel - RE: [RFC 09/20] iommu: Add page size and address width attributes

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Date:   Wed, 22 Sep 2021 14:19:14 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "jgg@...dia.com" <jgg@...dia.com>, "hch@....de" <hch@....de>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>
CC:     "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "lkml@...ux.net" <lkml@...ux.net>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "lushenming@...wei.com" <lushenming@...wei.com>,
        "corbet@....net" <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "yi.l.liu@...ux.intel.com" <yi.l.liu@...ux.intel.com>,
        "Tian, Jun J" <jun.j.tian@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "david@...son.dropbear.id.au" <david@...son.dropbear.id.au>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>
Subject: RE: [RFC 09/20] iommu: Add page size and address width attributes

> From: Eric Auger <eric.auger@...hat.com>
> Sent: Wednesday, September 22, 2021 9:43 PM
> 
> Hi,
> 
> On 9/19/21 8:38 AM, Liu Yi L wrote:
> > From: Lu Baolu <baolu.lu@...ux.intel.com>
> >
> > This exposes PAGE_SIZE and ADDR_WIDTH attributes. The iommufd could
> use
> > them to define the IOAS.
> >
> > Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> > ---
> >  include/linux/iommu.h | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index 943de6897f56..86d34e4ce05e 100644
> > --- a/include/linux/iommu.h
> > +++ b/include/linux/iommu.h
> > @@ -153,9 +153,13 @@ enum iommu_dev_features {
> >  /**
> >   * enum iommu_devattr - Per device IOMMU attributes
> >   * @IOMMU_DEV_INFO_FORCE_SNOOP [bool]: IOMMU can force DMA to
> be snooped.
> > + * @IOMMU_DEV_INFO_PAGE_SIZE [u64]: Page sizes that iommu
> supports.
> > + * @IOMMU_DEV_INFO_ADDR_WIDTH [u32]: Address width supported.
> I think this deserves additional info. What address width do we talk
> about, input, output, what stage if the IOMMU does support multiple stages
> 

it describes the address space width, thus is about input.

when multiple stages are supported, each stage is represented by a separate
ioasid, each with its own addr_width