RE: [PATCH v1 5/8] vfio/type1: Report 1st-level/stage-1 format to userspace

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Liu, Yi L <yi.l.liu@intel.com>
> Sent: Wednesday, April 1, 2020 3:38 PM
> 
>  > From: Tian, Kevin <kevin.tian@intel.com>
> > Sent: Monday, March 30, 2020 7:49 PM
> > To: Liu, Yi L <yi.l.liu@intel.com>; alex.williamson@redhat.com;
> > Subject: RE: [PATCH v1 5/8] vfio/type1: Report 1st-level/stage-1 format to
> > userspace
> >
> > > From: Liu, Yi L <yi.l.liu@intel.com>
> > > Sent: Sunday, March 22, 2020 8:32 PM
> > >
> > > From: Liu Yi L <yi.l.liu@intel.com>
> > >
> > > VFIO exposes IOMMU nesting translation (a.k.a dual stage translation)
> > > capability to userspace. Thus applications like QEMU could support
> > > vIOMMU with hardware's nesting translation capability for pass-through
> > > devices. Before setting up nesting translation for pass-through
> > > devices, QEMU and other applications need to learn the supported
> > > 1st-lvl/stage-1 translation structure format like page table format.
> > >
> > > Take vSVA (virtual Shared Virtual Addressing) as an example, to
> > > support vSVA for pass-through devices, QEMU setup nesting translation
> > > for pass- through devices. The guest page table are configured to host
> > > as 1st-lvl/
> > > stage-1 page table. Therefore, guest format should be compatible with
> > > host side.
> > >
> > > This patch reports the supported 1st-lvl/stage-1 page table format on
> > > the current platform to userspace. QEMU and other alike applications
> > > should use this format info when trying to setup IOMMU nesting
> > > translation on host IOMMU.
> > >
> > > Cc: Kevin Tian <kevin.tian@intel.com>
> > > CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > > Cc: Alex Williamson <alex.williamson@redhat.com>
> > > Cc: Eric Auger <eric.auger@redhat.com>
> > > Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > > Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> > > ---
> > >  drivers/vfio/vfio_iommu_type1.c | 56
> > > +++++++++++++++++++++++++++++++++++++++++
> > >  include/uapi/linux/vfio.h       |  1 +
> > >  2 files changed, 57 insertions(+)
> > >
> > > diff --git a/drivers/vfio/vfio_iommu_type1.c
> > > b/drivers/vfio/vfio_iommu_type1.c index 9aa2a67..82a9e0b 100644
> > > --- a/drivers/vfio/vfio_iommu_type1.c
> > > +++ b/drivers/vfio/vfio_iommu_type1.c
> > > @@ -2234,11 +2234,66 @@ static int
> vfio_iommu_type1_pasid_free(struct
> > > vfio_iommu *iommu,
> > >  	return ret;
> > >  }
> > >
> > > +static int vfio_iommu_get_stage1_format(struct vfio_iommu *iommu,
> > > +					 u32 *stage1_format)
> > > +{
> > > +	struct vfio_domain *domain;
> > > +	u32 format = 0, tmp_format = 0;
> > > +	int ret;
> > > +
> > > +	mutex_lock(&iommu->lock);
> > > +	if (list_empty(&iommu->domain_list)) {
> > > +		mutex_unlock(&iommu->lock);
> > > +		return -EINVAL;
> > > +	}
> > > +
> > > +	list_for_each_entry(domain, &iommu->domain_list, next) {
> > > +		if (iommu_domain_get_attr(domain->domain,
> > > +			DOMAIN_ATTR_PASID_FORMAT, &format)) {
> > > +			ret = -EINVAL;
> > > +			format = 0;
> > > +			goto out_unlock;
> > > +		}
> > > +		/*
> > > +		 * format is always non-zero (the first format is
> > > +		 * IOMMU_PASID_FORMAT_INTEL_VTD which is 1). For
> > > +		 * the reason of potential different backed IOMMU
> > > +		 * formats, here we expect to have identical formats
> > > +		 * in the domain list, no mixed formats support.
> > > +		 * return -EINVAL to fail the attempt of setup
> > > +		 * VFIO_TYPE1_NESTING_IOMMU if non-identical formats
> > > +		 * are detected.
> > > +		 */
> > > +		if (tmp_format && tmp_format != format) {
> > > +			ret = -EINVAL;
> > > +			format = 0;
> > > +			goto out_unlock;
> > > +		}
> > > +
> > > +		tmp_format = format;
> > > +	}
> >
> > this path is invoked only in VFIO_IOMMU_GET_INFO path. If we don't want
> to
> > assume the status quo that one container holds only one device w/
> vIOMMU
> > (the prerequisite for vSVA), looks we also need check the format
> > compatibility when attaching a new group to this container?
> 
> right. if attaching to a nesting type container (vfio_iommu.nesting bit
> indicates it), it should check if it is compabile with prior domains in
> the domain list. But if it is the first one attached to this container,
> it's fine. is it good?

yes, but my point is whether we should check the format compatibility
in the attach path...

> 
> > > +	ret = 0;
> > > +
> > > +out_unlock:
> > > +	if (format)
> > > +		*stage1_format = format;
> > > +	mutex_unlock(&iommu->lock);
> > > +	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;
> > > +	u32 formats = 0;
> > > +	int ret;
> > > +
> > > +	ret = vfio_iommu_get_stage1_format(iommu, &formats);
> > > +	if (ret) {
> > > +		pr_warn("Failed to get stage-1 format\n");
> > > +		return ret;
> > > +	}
> > >
> > >  	header = vfio_info_cap_add(caps, sizeof(*nesting_cap),
> > >  				   VFIO_IOMMU_TYPE1_INFO_CAP_NESTING,
> > > 1);
> > > @@ -2254,6 +2309,7 @@ static int
> > > vfio_iommu_info_add_nesting_cap(struct
> > > vfio_iommu *iommu,
> > >  		/* nesting iommu type supports PASID requests (alloc/free)
> */
> > >  		nesting_cap->nesting_capabilities |=
> VFIO_IOMMU_PASID_REQS;
> > >  	}
> > > +	nesting_cap->stage1_formats = formats;
> > >
> > >  	return 0;
> > >  }
> > > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > > index ed9881d..ebeaf3e 100644
> > > --- a/include/uapi/linux/vfio.h
> > > +++ b/include/uapi/linux/vfio.h
> > > @@ -763,6 +763,7 @@ struct vfio_iommu_type1_info_cap_nesting {
> > >  	struct	vfio_info_cap_header header;
> > >  #define VFIO_IOMMU_PASID_REQS	(1 << 0)
> > >  	__u32	nesting_capabilities;
> > > +	__u32	stage1_formats;
> >
> > do you plan to support multiple formats? If not, use singular name.
> 
> I do have such plan. e.g. it may be helpful when one day a platform can
> support multiple formats.
> 
> Regards,
> Yi Liu
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