RE: [PATCH v2 3/8] vfio: Change vfio_external_user_iommu_id() to vfio_file_iommu_group()

Tian, Kevin
2022-04-20T23:40:17Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Thursday, April 21, 2022 3:23 AM
>
> The only user wants to get a pointer to the struct iommu_group associated
> with the VFIO group file being used. Instead of returning the group ID
> then searching sysfs for that string just directly return the iommu_group
> pointer already held by the vfio_group struct.
>
> It already has a safe lifetime due to the struct file kref, the vfio_group
> and thus the iommu_group cannot be destroyed while the group file is open.
>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

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

> ---
> drivers/vfio/vfio.c | 21 ++++++++++++++-------
> include/linux/vfio.h | 2 +-
> virt/kvm/vfio.c | 37 ++++++++++++-------------------------
> 3 files changed, 27 insertions(+), 33 deletions(-)
>
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index a4555014bd1e72..3444d36714e933 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -1919,10 +1919,7 @@ static const struct file_operations
> vfio_device_fops = {
> * increments the container user counter to prevent
> * the VFIO group from disposal before KVM exits.
> *
> - * 3. The external user calls vfio_external_user_iommu_id()
> - * to know an IOMMU ID.
> - *
> - * 4. When the external KVM finishes, it calls
> + * 3. When the external KVM finishes, it calls
> * vfio_group_put_external_user() to release the VFIO group.
> * This call decrements the container user counter.
> */
> @@ -2001,11 +1998,21 @@ bool vfio_external_group_match_file(struct
> vfio_group *test_group,
> }
> EXPORT_SYMBOL_GPL(vfio_external_group_match_file);
>
> -int vfio_external_user_iommu_id(struct vfio_group *group)
> +/**
> + * vfio_file_iommu_group - Return the struct iommu_group for the vfio
> group file
> + * @file: VFIO group file
> + *
> + * The returned iommu_group is valid as long as a ref is held on the file.
> + */
> +struct iommu_group *vfio_file_iommu_group(struct file *file)
> {
> - return iommu_group_id(group->iommu_group);
> + struct vfio_group *group = file->private_data;
> +
> + if (file->f_op != &vfio_group_fops)
> + return NULL;
> + return group->iommu_group;
> }
> -EXPORT_SYMBOL_GPL(vfio_external_user_iommu_id);
> +EXPORT_SYMBOL_GPL(vfio_file_iommu_group);
>
> long vfio_external_check_extension(struct vfio_group *group, unsigned long
> arg)
> {
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index 66dda06ec42d1b..8b53fd9920d24a 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -144,7 +144,7 @@ extern struct vfio_group
> *vfio_group_get_external_user_from_dev(struct device
> *dev);
> extern bool vfio_external_group_match_file(struct vfio_group *group,
> struct file *filep);
> -extern int vfio_external_user_iommu_id(struct vfio_group *group);
> +extern struct iommu_group *vfio_file_iommu_group(struct file *file);
> extern long vfio_external_check_extension(struct vfio_group *group,
> unsigned long arg);
>
> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
> index 07ee54a62b560d..1655d3aebd16b4 100644
> --- a/virt/kvm/vfio.c
> +++ b/virt/kvm/vfio.c
> @@ -108,43 +108,31 @@ static bool kvm_vfio_group_is_coherent(struct
> vfio_group *vfio_group)
> }
>
> #ifdef CONFIG_SPAPR_TCE_IOMMU
> -static int kvm_vfio_external_user_iommu_id(struct vfio_group *vfio_group)
> +static struct iommu_group *kvm_vfio_file_iommu_group(struct file *file)
> {
> - int (*fn)(struct vfio_group *);
> - int ret = -EINVAL;
> + struct iommu_group *(*fn)(struct file *file);
> + struct iommu_group *ret;
>
> - fn = symbol_get(vfio_external_user_iommu_id);
> + fn = symbol_get(vfio_file_iommu_group);
> if (!fn)
> - return ret;
> + return NULL;
>
> - ret = fn(vfio_group);
> + ret = fn(file);
>
> - symbol_put(vfio_external_user_iommu_id);
> + symbol_put(vfio_file_iommu_group);
>
> return ret;
> }
>
> -static struct iommu_group *kvm_vfio_group_get_iommu_group(
> - struct vfio_group *group)
> -{
> - int group_id = kvm_vfio_external_user_iommu_id(group);
> -
> - if (group_id < 0)
> - return NULL;
> -
> - return iommu_group_get_by_id(group_id);
> -}
> -
> static void kvm_spapr_tce_release_vfio_group(struct kvm *kvm,
> - struct vfio_group *vfio_group)
> + struct kvm_vfio_group *kvg)
> {
> - struct iommu_group *grp =
> kvm_vfio_group_get_iommu_group(vfio_group);
> + struct iommu_group *grp = kvm_vfio_file_iommu_group(kvg->file);
>
> if (WARN_ON_ONCE(!grp))
> return;
>
> kvm_spapr_tce_release_iommu_group(kvm, grp);
> - iommu_group_put(grp);
> }
> #endif
>
> @@ -258,7 +246,7 @@ static int kvm_vfio_group_del(struct kvm_device
> *dev, unsigned int fd)
> list_del(&kvg->node);
> kvm_arch_end_assignment(dev->kvm);
> #ifdef CONFIG_SPAPR_TCE_IOMMU
> - kvm_spapr_tce_release_vfio_group(dev->kvm, kvg-
> >vfio_group);
> + kvm_spapr_tce_release_vfio_group(dev->kvm, kvg);
> #endif
> kvm_vfio_group_set_kvm(kvg->vfio_group, NULL);
> kvm_vfio_group_put_external_user(kvg->vfio_group);
> @@ -304,7 +292,7 @@ static int kvm_vfio_group_set_spapr_tce(struct
> kvm_device *dev,
> if (kvg->file != f.file)
> continue;
>
> - grp = kvm_vfio_group_get_iommu_group(kvg->vfio_group);
> + grp = kvm_vfio_file_iommu_group(kvg->file);
> if (WARN_ON_ONCE(!grp)) {
> ret = -EIO;
> goto err_fdput;
> @@ -312,7 +300,6 @@ static int kvm_vfio_group_set_spapr_tce(struct
> kvm_device *dev,
>
> ret = kvm_spapr_tce_attach_iommu_group(dev->kvm,
> param.tablefd,
> grp);
> - iommu_group_put(grp);
> break;
> }
>
> @@ -386,7 +373,7 @@ static void kvm_vfio_destroy(struct kvm_device *dev)
>
> list_for_each_entry_safe(kvg, tmp, &kv->group_list, node) {
> #ifdef CONFIG_SPAPR_TCE_IOMMU
> - kvm_spapr_tce_release_vfio_group(dev->kvm, kvg-
> >vfio_group);
> + kvm_spapr_tce_release_vfio_group(dev->kvm, kvg);
> #endif
> kvm_vfio_group_set_kvm(kvg->vfio_group, NULL);
> kvm_vfio_group_put_external_user(kvg->vfio_group);
> --
> 2.36.0