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Date: Wed, 22 Sep 2021 03:30:09 +0000 From: "Tian, Kevin" <kevin.tian@...el.com> To: Jason Gunthorpe <jgg@...dia.com>, "Liu, Yi L" <yi.l.liu@...el.com> CC: "alex.williamson@...hat.com" <alex.williamson@...hat.com>, "hch@....de" <hch@....de>, "jasowang@...hat.com" <jasowang@...hat.com>, "joro@...tes.org" <joro@...tes.org>, "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>, "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>, "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 10/20] iommu/iommufd: Add IOMMU_DEVICE_GET_INFO > From: Jason Gunthorpe <jgg@...dia.com> > Sent: Wednesday, September 22, 2021 1:41 AM > > On Sun, Sep 19, 2021 at 02:38:38PM +0800, Liu Yi L wrote: > > After a device is bound to the iommufd, userspace can use this interface > > to query the underlying iommu capability and format info for this device. > > Based on this information the user then creates I/O address space in a > > compatible format with the to-be-attached devices. > > > > Device cookie which is registered at binding time is used to mark the > > device which is being queried here. > > > > Signed-off-by: Liu Yi L <yi.l.liu@...el.com> > > drivers/iommu/iommufd/iommufd.c | 68 > +++++++++++++++++++++++++++++++++ > > include/uapi/linux/iommu.h | 49 ++++++++++++++++++++++++ > > 2 files changed, 117 insertions(+) > > > > diff --git a/drivers/iommu/iommufd/iommufd.c > b/drivers/iommu/iommufd/iommufd.c > > index e16ca21e4534..641f199f2d41 100644 > > +++ b/drivers/iommu/iommufd/iommufd.c > > @@ -117,6 +117,71 @@ static int iommufd_fops_release(struct inode > *inode, struct file *filep) > > return 0; > > } > > > > +static struct device * > > +iommu_find_device_from_cookie(struct iommufd_ctx *ictx, u64 > dev_cookie) > > +{ > > We have an xarray ID for the device, why are we allowing userspace to > use the dev_cookie as input? > > Userspace should always pass in the ID. The only place dev_cookie > should appear is if the kernel generates an event back to > userspace. Then the kernel should return both the ID and the > dev_cookie in the event to allow userspace to correlate it. > A little background. In earlier design proposal we discussed two options. One is to return an kernel-allocated ID (label) to userspace. The other is to have user register a cookie and use it in iommufd uAPI. At that time the two options were discussed exclusively and the cookie one is preferred. Now you instead recommended a mixed option. We can follow it for sure if nobody objects. Thanks Kevin
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