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