linux-kernel - RE: [RFC 17/20] iommu/iommufd: Report iova range to userspace

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Message-ID: <PH0PR11MB56580CB47CA2CF17C86CD0D0C3A99@PH0PR11MB5658.namprd11.prod.outlook.com>
Date:   Wed, 29 Sep 2021 10:44:01 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
CC:     "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>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "parav@...lanox.com" <parav@...lanox.com>,
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        "eric.auger@...hat.com" <eric.auger@...hat.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>,
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        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
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Subject: RE: [RFC 17/20] iommu/iommufd: Report iova range to userspace

> From: Jean-Philippe Brucker <jean-philippe@...aro.org>
> Sent: Wednesday, September 22, 2021 10:49 PM
> 
> On Sun, Sep 19, 2021 at 02:38:45PM +0800, Liu Yi L wrote:
> > [HACK. will fix in v2]
> >
> > IOVA range is critical info for userspace to manage DMA for an I/O address
> > space. This patch reports the valid iova range info of a given device.
> >
> > Due to aforementioned hack, this info comes from the hacked vfio type1
> > driver. To follow the same format in vfio, we also introduce a cap chain
> > format in IOMMU_DEVICE_GET_INFO to carry the iova range info.
> [...]
> > diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
> > index 49731be71213..f408ad3c8ade 100644
> > --- a/include/uapi/linux/iommu.h
> > +++ b/include/uapi/linux/iommu.h
> > @@ -68,6 +68,7 @@
> >   *		   +---------------+------------+
> >   *		   ...
> >   * @addr_width:    the address width of supported I/O address spaces.
> > + * @cap_offset:	   Offset within info struct of first cap
> >   *
> >   * Availability: after device is bound to iommufd
> >   */
> > @@ -77,9 +78,11 @@ struct iommu_device_info {
> >  #define IOMMU_DEVICE_INFO_ENFORCE_SNOOP	(1 << 0) /* IOMMU
> enforced snoop */
> >  #define IOMMU_DEVICE_INFO_PGSIZES	(1 << 1) /* supported page
> sizes */
> >  #define IOMMU_DEVICE_INFO_ADDR_WIDTH	(1 << 2) /*
> addr_wdith field valid */
> > +#define IOMMU_DEVICE_INFO_CAPS		(1 << 3) /* info
> supports cap chain */
> >  	__u64	dev_cookie;
> >  	__u64   pgsize_bitmap;
> >  	__u32	addr_width;
> > +	__u32   cap_offset;
> 
> We can also add vendor-specific page table and PASID table properties as
> capabilities, otherwise we'll need giant unions in the iommu_device_info
> struct. That made me wonder whether pgsize and addr_width should also
> be
> separate capabilities for consistency, but this way might be good enough.
> There won't be many more generic capabilities. I have "output address
> width"

what do you mean by "output address width"? Is it the output address
of stage-1 translation?

>
and "PASID width", the rest is specific to Arm and SMMU table
> formats.

When coming to nested translation support, the stage-1 related info are
likely to be vendor-specific, and will be reported in cap chain.

Regards,
Yi Liu

> Thanks,
> Jean
> 
> >  };
> >
> >  #define IOMMU_DEVICE_GET_INFO	_IO(IOMMU_TYPE, IOMMU_BASE +
> 1)
> > --
> > 2.25.1
> >