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

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Message-ID: <20210922133217.GR327412@nvidia.com>
Date:   Wed, 22 Sep 2021 10:32:17 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "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>,
        "Tian, Kevin" <kevin.tian@...el.com>,
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        "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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Subject: Re: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID_ALLOC/FREE

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.

Jason