linux-kernel - RE: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID

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Date:   Thu, 23 Sep 2021 06:26:39 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Jason Gunthorpe <jgg@...dia.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>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "parav@...lanox.com" <parav@...lanox.com>,
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        "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>,
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        "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>,
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Subject: RE: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID_ALLOC/FREE

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Wednesday, September 22, 2021 9:32 PM
> 
> On Wed, Sep 22, 2021 at 12:51:38PM +0000, Liu, Yi L wrote:
> > > From: Jason Gunthorpe <jgg@...dia.com>
> > > Sent: Wednesday, September 22, 2021 1:45 AM
> > >
> > [...]
> > > > diff --git a/drivers/iommu/iommufd/iommufd.c
> > > b/drivers/iommu/iommufd/iommufd.c
> > > > index 641f199f2d41..4839f128b24a 100644
> > > > +++ b/drivers/iommu/iommufd/iommufd.c
> > > > @@ -24,6 +24,7 @@
> > > >  struct iommufd_ctx {
> > > >  	refcount_t refs;
> > > >  	struct mutex lock;
> > > > +	struct xarray ioasid_xa; /* xarray of ioasids */
> > > >  	struct xarray device_xa; /* xarray of bound devices */
> > > >  };
> > > >
> > > > @@ -42,6 +43,16 @@ struct iommufd_device {
> > > >  	u64 dev_cookie;
> > > >  };
> > > >
> > > > +/* Represent an I/O address space */
> > > > +struct iommufd_ioas {
> > > > +	int ioasid;
> > >
> > > xarray id's should consistently be u32s everywhere.
> >
> > sure. just one more check, this id is supposed to be returned to
> > userspace as the return value of ioctl(IOASID_ALLOC). That's why
> > I chose to use "int" as its prototype to make it aligned with the
> > return type of ioctl(). Based on this, do you think it's still better
> > to use "u32" here?
> 
> I suggest not using the return code from ioctl to exchange data.. The
> rest of the uAPI uses an in/out struct, everything should do
> that consistently.

got it.

Thanks,
Yi Liu