Re: [PATCH v1 6/8] vfio/type1: Bind guest page tables to host

[Jean-Philippe Brucker]

On Tue, Apr 07, 2020 at 10:33:25AM +0000, Liu, Yi L wrote:
> Hi Jean,
> 
> > From: Jean-Philippe Brucker < jean-philippe@xxxxxxxxxx >
> > Sent: Friday, April 3, 2020 4:35 PM
> > Subject: Re: [PATCH v1 6/8] vfio/type1: Bind guest page tables to host
> > 
> > On Thu, Apr 02, 2020 at 08:05:29AM +0000, Liu, Yi L wrote:
> > > > > > > static long vfio_iommu_type1_ioctl(void *iommu_data,
> > > > > > >  		default:
> > > > > > >  			return -EINVAL;
> > > > > > >  		}
> > > > > > > +
> > > > > > > +	} else if (cmd == VFIO_IOMMU_BIND) {
> > > > > >
> > > > > > BIND what? VFIO_IOMMU_BIND_PASID sounds clearer to me.
> > > > >
> > > > > Emm, it's up to the flags to indicate bind what. It was proposed to
> > > > > cover the three cases below:
> > > > > a) BIND/UNBIND_GPASID
> > > > > b) BIND/UNBIND_GPASID_TABLE
> > > > > c) BIND/UNBIND_PROCESS
> > > > > <only a) is covered in this patch>
> > > > > So it's called VFIO_IOMMU_BIND.
> > > >
> > > > but aren't they all about PASID related binding?
> > >
> > > yeah, I can rename it. :-)
> > 
> > I don't know if anyone intends to implement it, but SMMUv2 supports
> > nesting translation without any PASID support. For that case the name
> > VFIO_IOMMU_BIND_GUEST_PGTBL without "PASID" anywhere makes more sense.
> > Ideally we'd also use a neutral name for the IOMMU API instead of
> > bind_gpasid(), but that's easier to change later.
> 
> I agree VFIO_IOMMU_BIND is somehow not straight-forward. Especially, it may
> cause confusion when thinking about VFIO_SET_IOMMU. How about using
> VFIO_NESTING_IOMMU_BIND_STAGE1 to cover a) and b)? And has another
> VFIO_BIND_PROCESS in future for the SVA bind case.

I think minimizing the number of ioctls is more important than finding the
ideal name. VFIO_IOMMU_BIND was fine to me, but if it's too vague then
rename it to VFIO_IOMMU_BIND_PASID and we'll just piggy-back on it for
non-PASID things (they should be rare enough).

Thanks,
Jean