Re: [PATCH v2 5/9] iommu/ioasid: Introduce ioasid_set private ID

[Jean-Philippe Brucker]

On Fri, Aug 21, 2020 at 09:35:14PM -0700, Jacob Pan wrote:
> When an IOASID set is used for guest SVA, each VM will acquire its
> ioasid_set for IOASID allocations. IOASIDs within the VM must have a
> host/physical IOASID backing, mapping between guest and host IOASIDs can
> be non-identical. IOASID set private ID (SPID) is introduced in this
> patch to be used as guest IOASID. However, the concept of ioasid_set
> specific namespace is generic, thus named SPID.
> 
> As SPID namespace is within the IOASID set, the IOASID core can provide
> lookup services at both directions. SPIDs may not be allocated when its
> IOASID is allocated, the mapping between SPID and IOASID is usually
> established when a guest page table is bound to a host PASID.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> ---
>  drivers/iommu/ioasid.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/ioasid.h | 12 +++++++++++
>  2 files changed, 66 insertions(+)
> 
> diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
> index 5f31d63c75b1..c0aef38a4fde 100644
> --- a/drivers/iommu/ioasid.c
> +++ b/drivers/iommu/ioasid.c
> @@ -21,6 +21,7 @@ enum ioasid_state {
>   * struct ioasid_data - Meta data about ioasid
>   *
>   * @id:		Unique ID
> + * @spid:	Private ID unique within a set
>   * @users	Number of active users
>   * @state	Track state of the IOASID
>   * @set		Meta data of the set this IOASID belongs to
> @@ -29,6 +30,7 @@ enum ioasid_state {
>   */
>  struct ioasid_data {
>  	ioasid_t id;
> +	ioasid_t spid;
>  	struct ioasid_set *set;
>  	refcount_t users;
>  	enum ioasid_state state;
> @@ -326,6 +328,58 @@ int ioasid_attach_data(ioasid_t ioasid, void *data)
>  EXPORT_SYMBOL_GPL(ioasid_attach_data);
>  
>  /**
> + * ioasid_attach_spid - Attach ioasid_set private ID to an IOASID
> + *
> + * @ioasid: the ID to attach
> + * @spid:   the ioasid_set private ID of @ioasid
> + *
> + * For IOASID that is already allocated, private ID within the set can be
> + * attached via this API. Future lookup can be done via ioasid_find.

via ioasid_find_by_spid()?

> + */
> +int ioasid_attach_spid(ioasid_t ioasid, ioasid_t spid)
> +{
> +	struct ioasid_data *ioasid_data;
> +	int ret = 0;
> +
> +	spin_lock(&ioasid_allocator_lock);
> +	ioasid_data = xa_load(&active_allocator->xa, ioasid);
> +
> +	if (!ioasid_data) {
> +		pr_err("No IOASID entry %d to attach SPID %d\n",
> +			ioasid, spid);
> +		ret = -ENOENT;
> +		goto done_unlock;
> +	}
> +	ioasid_data->spid = spid;
> +
> +done_unlock:
> +	spin_unlock(&ioasid_allocator_lock);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_attach_spid);
> +
> +ioasid_t ioasid_find_by_spid(struct ioasid_set *set, ioasid_t spid)

Maybe add a bit of documentation as this is public-facing.

> +{
> +	struct ioasid_data *entry;
> +	unsigned long index;
> +
> +	if (!xa_load(&ioasid_sets, set->sid)) {
> +		pr_warn("Invalid set\n");
> +		return INVALID_IOASID;
> +	}
> +
> +	xa_for_each(&set->xa, index, entry) {
> +		if (spid == entry->spid) {
> +			pr_debug("Found ioasid %lu by spid %u\n", index, spid);
> +			refcount_inc(&entry->users);

Nothing prevents ioasid_free() from concurrently dropping the refcount to
zero and calling ioasid_do_free(). The caller will later call ioasid_put()
on a stale/reallocated index.

> +			return index;
> +		}
> +	}
> +	return INVALID_IOASID;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_find_by_spid);
> +
> +/**
>   * ioasid_alloc - Allocate an IOASID
>   * @set: the IOASID set
>   * @min: the minimum ID (inclusive)
> diff --git a/include/linux/ioasid.h b/include/linux/ioasid.h
> index 310abe4187a3..d4b3e83672f6 100644
> --- a/include/linux/ioasid.h
> +++ b/include/linux/ioasid.h
> @@ -73,6 +73,8 @@ bool ioasid_is_active(ioasid_t ioasid);
>  
>  void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid, bool (*getter)(void *));
>  int ioasid_attach_data(ioasid_t ioasid, void *data);
> +int ioasid_attach_spid(ioasid_t ioasid, ioasid_t spid);
> +ioasid_t ioasid_find_by_spid(struct ioasid_set *set, ioasid_t spid);
>  int ioasid_register_allocator(struct ioasid_allocator_ops *allocator);
>  void ioasid_unregister_allocator(struct ioasid_allocator_ops *allocator);
>  void ioasid_is_in_set(struct ioasid_set *set, ioasid_t ioasid);
> @@ -136,5 +138,15 @@ static inline int ioasid_attach_data(ioasid_t ioasid, void *data)
>  	return -ENOTSUPP;
>  }
>  
> +staic inline int ioasid_attach_spid(ioasid_t ioasid, ioasid_t spid)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static inline ioasid_t ioasid_find_by_spid(struct ioasid_set *set, ioasid_t spid)
> +{
> +	return -ENOTSUPP;

INVALID_IOASID

Thanks,
Jean

> +}
> +
>  #endif /* CONFIG_IOASID */
>  #endif /* __LINUX_IOASID_H */
> -- 
> 2.7.4
>