Re: [PATCH v1 8/8] vfio/type1: Add vSVA support for IOMMU-backed mdevs

Alex Williamson
2020-04-02T20:34:24Z

On Sun, 22 Mar 2020 05:32:05 -0700
"Liu, Yi L" <yi.l.liu@intel.com> wrote:

> From: Liu Yi L <yi.l.liu@intel.com>
>
> Recent years, mediated device pass-through framework (e.g. vfio-mdev)
> are used to achieve flexible device sharing across domains (e.g. VMs).
> Also there are hardware assisted mediated pass-through solutions from
> platform vendors. e.g. Intel VT-d scalable mode which supports Intel
> Scalable I/O Virtualization technology. Such mdevs are called IOMMU-
> backed mdevs as there are IOMMU enforced DMA isolation for such mdevs.
> In kernel, IOMMU-backed mdevs are exposed to IOMMU layer by aux-domain
> concept, which means mdevs are protected by an iommu domain which is
> aux-domain of its physical device. Details can be found in the KVM
> presentation from Kevin Tian. IOMMU-backed equals to IOMMU-capable.
>
> https://events19.linuxfoundation.org/wp-content/uploads/2017/12/\
> Hardware-Assisted-Mediated-Pass-Through-with-VFIO-Kevin-Tian-Intel.pdf
>
> This patch supports NESTING IOMMU for IOMMU-backed mdevs by figuring
> out the physical device of an IOMMU-backed mdev and then invoking IOMMU
> requests to IOMMU layer with the physical device and the mdev's aux
> domain info.
>
> With this patch, vSVA (Virtual Shared Virtual Addressing) can be used
> on IOMMU-backed mdevs.
>
> Cc: Kevin Tian <kevin.tian@intel.com>
> CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
> CC: Jun Tian <jun.j.tian@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 | 23 ++++++++++++++++++++---
> 1 file changed, 20 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 937ec3f..d473665 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -132,6 +132,7 @@ struct vfio_regions {
>
> struct domain_capsule {
> struct iommu_domain *domain;
> + struct vfio_group *group;
> void *data;
> };
>
> @@ -148,6 +149,7 @@ static int vfio_iommu_for_each_dev(struct vfio_iommu *iommu,
> list_for_each_entry(d, &iommu->domain_list, next) {
> dc.domain = d->domain;
> list_for_each_entry(g, &d->group_list, next) {
> + dc.group = g;
> ret = iommu_group_for_each_dev(g->iommu_group,
> &dc, fn);
> if (ret)
> @@ -2347,7 +2349,12 @@ static int vfio_bind_gpasid_fn(struct device *dev, void *data)
> struct iommu_gpasid_bind_data *gbind_data =
> (struct iommu_gpasid_bind_data *) dc->data;
>
> - return iommu_sva_bind_gpasid(dc->domain, dev, gbind_data);
> + if (dc->group->mdev_group)
> + return iommu_sva_bind_gpasid(dc->domain,
> + vfio_mdev_get_iommu_device(dev), gbind_data);

But we can't assume an mdev device is iommu backed, so this can call
with NULL dev, which appears will pretty quickly segfault
intel_svm_bind_gpasid.

> + else
> + return iommu_sva_bind_gpasid(dc->domain,
> + dev, gbind_data);
> }
>
> static int vfio_unbind_gpasid_fn(struct device *dev, void *data)
> @@ -2356,8 +2363,13 @@ static int vfio_unbind_gpasid_fn(struct device *dev, void *data)
> struct iommu_gpasid_bind_data *gbind_data =
> (struct iommu_gpasid_bind_data *) dc->data;
>
> - return iommu_sva_unbind_gpasid(dc->domain, dev,
> + if (dc->group->mdev_group)
> + return iommu_sva_unbind_gpasid(dc->domain,
> + vfio_mdev_get_iommu_device(dev),
> gbind_data->hpasid);

Same

> + else
> + return iommu_sva_unbind_gpasid(dc->domain, dev,
> + gbind_data->hpasid);
> }
>
> /**
> @@ -2429,7 +2441,12 @@ static int vfio_cache_inv_fn(struct device *dev, void *data)
> struct iommu_cache_invalidate_info *cache_inv_info =
> (struct iommu_cache_invalidate_info *) dc->data;
>
> - return iommu_cache_invalidate(dc->domain, dev, cache_inv_info);
> + if (dc->group->mdev_group)
> + return iommu_cache_invalidate(dc->domain,
> + vfio_mdev_get_iommu_device(dev), cache_inv_info);

And again

> + else
> + return iommu_cache_invalidate(dc->domain,
> + dev, cache_inv_info);
> }
>
> static long vfio_iommu_type1_ioctl(void *iommu_data,