RE: [PATCH v2 7/8] kvm/vfio: Remove vfio_group from kvm

Tian, Kevin
2022-04-20T23:55:20Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Thursday, April 21, 2022 3:23 AM
>
> None of the VFIO APIs take in the vfio_group anymore, so we can remove it
> completely.
>
> This has a subtle side effect on the enforced coherency tracking. The
> vfio_group_get_external_user() was holding on to the container_users which
> would prevent the iommu_domain and thus the enforced coherency value
> from
> changing while the group is registered with kvm.
>
> It changes the security proof slightly into 'user must hold a group FD
> that has a device that cannot enforce DMA coherence'. As opening the group
> FD, not attaching the container, is the privileged operation this doesn't
> change the security properties much.
>
> On the flip side it paves the way to changing the iommu_domain/container
> attached to a group at runtime which is something that will be required to
> support nested translation.
>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Other than whether to check error on enforced coherency:

Reviewed-by: Kevin Tian <kevin.tian@intel.com>

> ---
> virt/kvm/vfio.c | 51 ++++++++-----------------------------------------
> 1 file changed, 8 insertions(+), 43 deletions(-)
>
> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
> index 2aeb53247001cc..f78c2fe3659c1a 100644
> --- a/virt/kvm/vfio.c
> +++ b/virt/kvm/vfio.c
> @@ -24,7 +24,6 @@
> struct kvm_vfio_group {
> struct list_head node;
> struct file *file;
> - struct vfio_group *vfio_group;
> };
>
> struct kvm_vfio {
> @@ -33,35 +32,6 @@ struct kvm_vfio {
> bool noncoherent;
> };
>
> -static struct vfio_group *kvm_vfio_group_get_external_user(struct file *filep)
> -{
> - struct vfio_group *vfio_group;
> - struct vfio_group *(*fn)(struct file *);
> -
> - fn = symbol_get(vfio_group_get_external_user);
> - if (!fn)
> - return ERR_PTR(-EINVAL);
> -
> - vfio_group = fn(filep);
> -
> - symbol_put(vfio_group_get_external_user);
> -
> - return vfio_group;
> -}
> -
> -static void kvm_vfio_group_put_external_user(struct vfio_group
> *vfio_group)
> -{
> - void (*fn)(struct vfio_group *);
> -
> - fn = symbol_get(vfio_group_put_external_user);
> - if (!fn)
> - return;
> -
> - fn(vfio_group);
> -
> - symbol_put(vfio_group_put_external_user);
> -}
> -
> static void kvm_vfio_file_set_kvm(struct file *file, struct kvm *kvm)
> {
> void (*fn)(struct file *file, struct kvm *kvm);
> @@ -91,7 +61,6 @@ static bool kvm_vfio_file_enforced_coherent(struct file
> *file)
> return ret;
> }
>
> -#ifdef CONFIG_SPAPR_TCE_IOMMU
> static struct iommu_group *kvm_vfio_file_iommu_group(struct file *file)
> {
> struct iommu_group *(*fn)(struct file *file);
> @@ -108,6 +77,7 @@ static struct iommu_group
> *kvm_vfio_file_iommu_group(struct file *file)
> return ret;
> }
>
> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> static void kvm_spapr_tce_release_vfio_group(struct kvm *kvm,
> struct kvm_vfio_group *kvg)
> {
> @@ -157,7 +127,6 @@ static void kvm_vfio_update_coherency(struct
> kvm_device *dev)
> static int kvm_vfio_group_add(struct kvm_device *dev, unsigned int fd)
> {
> struct kvm_vfio *kv = dev->private;
> - struct vfio_group *vfio_group;
> struct kvm_vfio_group *kvg;
> struct file *filp;
> int ret;
> @@ -166,6 +135,12 @@ static int kvm_vfio_group_add(struct kvm_device
> *dev, unsigned int fd)
> if (!filp)
> return -EBADF;
>
> + /* Ensure the FD is a vfio group FD.*/
> + if (!kvm_vfio_file_iommu_group(filp)) {
> + ret = -EINVAL;
> + goto err_fput;
> + }
> +
> mutex_lock(&kv->lock);
>
> list_for_each_entry(kvg, &kv->group_list, node) {
> @@ -181,15 +156,8 @@ static int kvm_vfio_group_add(struct kvm_device
> *dev, unsigned int fd)
> goto err_unlock;
> }
>
> - vfio_group = kvm_vfio_group_get_external_user(filp);
> - if (IS_ERR(vfio_group)) {
> - ret = PTR_ERR(vfio_group);
> - goto err_free;
> - }
> -
> kvg->file = filp;
> list_add_tail(&kvg->node, &kv->group_list);
> - kvg->vfio_group = vfio_group;
>
> kvm_arch_start_assignment(dev->kvm);
>
> @@ -199,10 +167,9 @@ static int kvm_vfio_group_add(struct kvm_device
> *dev, unsigned int fd)
> kvm_vfio_update_coherency(dev);
>
> return 0;
> -err_free:
> - kfree(kvg);
> err_unlock:
> mutex_unlock(&kv->lock);
> +err_fput:
> fput(filp);
> return ret;
> }
> @@ -232,7 +199,6 @@ static int kvm_vfio_group_del(struct kvm_device
> *dev, unsigned int fd)
> kvm_spapr_tce_release_vfio_group(dev->kvm, kvg);
> #endif
> kvm_vfio_file_set_kvm(kvg->file, NULL);
> - kvm_vfio_group_put_external_user(kvg->vfio_group);
> fput(kvg->file);
> kfree(kvg);
> ret = 0;
> @@ -359,7 +325,6 @@ static void kvm_vfio_destroy(struct kvm_device *dev)
> kvm_spapr_tce_release_vfio_group(dev->kvm, kvg);
> #endif
> kvm_vfio_file_set_kvm(kvg->file, NULL);
> - kvm_vfio_group_put_external_user(kvg->vfio_group);
> fput(kvg->file);
> list_del(&kvg->node);
> kfree(kvg);
> --
> 2.36.0