RE: [PATCH v1 3/8] vfio/type1: Report PASID alloc/free support to userspace

[Liu, Yi L]

Hi Eric,

> From: Auger Eric <eric.auger@xxxxxxxxxx>
> Sent: Wednesday, April 1, 2020 5:41 PM
> To: Liu, Yi L <yi.l.liu@xxxxxxxxx>; alex.williamson@xxxxxxxxxx
> Subject: Re: [PATCH v1 3/8] vfio/type1: Report PASID alloc/free support to
> userspace
> 
> Yi,
> On 3/22/20 1:32 PM, Liu, Yi L wrote:
> > From: Liu Yi L <yi.l.liu@xxxxxxxxx>
> >
> > This patch reports PASID alloc/free availability to userspace (e.g.
> > QEMU) thus userspace could do a pre-check before utilizing this feature.
> >
> > Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
> > CC: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> > Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > Cc: Eric Auger <eric.auger@xxxxxxxxxx>
> > Cc: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> > Signed-off-by: Liu Yi L <yi.l.liu@xxxxxxxxx>
> > ---
> >  drivers/vfio/vfio_iommu_type1.c | 28 ++++++++++++++++++++++++++++
> >  include/uapi/linux/vfio.h       |  8 ++++++++
> >  2 files changed, 36 insertions(+)
> >
> > diff --git a/drivers/vfio/vfio_iommu_type1.c
> > b/drivers/vfio/vfio_iommu_type1.c index e40afc0..ddd1ffe 100644
> > --- a/drivers/vfio/vfio_iommu_type1.c
> > +++ b/drivers/vfio/vfio_iommu_type1.c
> > @@ -2234,6 +2234,30 @@ static int vfio_iommu_type1_pasid_free(struct
> vfio_iommu *iommu,
> >  	return ret;
> >  }
> >
> > +static int vfio_iommu_info_add_nesting_cap(struct vfio_iommu *iommu,
> > +					 struct vfio_info_cap *caps)
> > +{
> > +	struct vfio_info_cap_header *header;
> > +	struct vfio_iommu_type1_info_cap_nesting *nesting_cap;
> > +
> > +	header = vfio_info_cap_add(caps, sizeof(*nesting_cap),
> > +				   VFIO_IOMMU_TYPE1_INFO_CAP_NESTING, 1);
> > +	if (IS_ERR(header))
> > +		return PTR_ERR(header);
> > +
> > +	nesting_cap = container_of(header,
> > +				struct vfio_iommu_type1_info_cap_nesting,
> > +				header);
> > +
> > +	nesting_cap->nesting_capabilities = 0;
> > +	if (iommu->nesting) {
> > +		/* nesting iommu type supports PASID requests (alloc/free) */
> > +		nesting_cap->nesting_capabilities |= VFIO_IOMMU_PASID_REQS;
> Supporting nesting does not necessarily mean supporting PASID.

here I think the PASID is somehow IDs in kernel which can be used to
tag various address spaces provided by guest software. I think this
is why we introduced the ioasid. :-) Current implementation is doing
PASID alloc/free in vfio.

> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >  static long vfio_iommu_type1_ioctl(void *iommu_data,
> >  				   unsigned int cmd, unsigned long arg)  { @@ -
> 2283,6 +2307,10 @@
> > static long vfio_iommu_type1_ioctl(void *iommu_data,
> >  		if (ret)
> >  			return ret;
> >
> > +		ret = vfio_iommu_info_add_nesting_cap(iommu, &caps);
> > +		if (ret)
> > +			return ret;
> > +
> >  		if (caps.size) {
> >  			info.flags |= VFIO_IOMMU_INFO_CAPS;
> >
> > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > index 298ac80..8837219 100644
> > --- a/include/uapi/linux/vfio.h
> > +++ b/include/uapi/linux/vfio.h
> > @@ -748,6 +748,14 @@ struct vfio_iommu_type1_info_cap_iova_range {
> >  	struct	vfio_iova_range iova_ranges[];
> >  };
> >
> > +#define VFIO_IOMMU_TYPE1_INFO_CAP_NESTING  2
> > +
> > +struct vfio_iommu_type1_info_cap_nesting {
> > +	struct	vfio_info_cap_header header;
> > +#define VFIO_IOMMU_PASID_REQS	(1 << 0)
> PASID_REQS sounds a bit far from the claimed host managed alloc/free
> capability.
> VFIO_IOMMU_SYSTEM_WIDE_PASID?

Oh, yep. I can rename it.

Regards,
Yi Liu