Re: [PATCH v6 1/9] iommu: Add APIs for multiple domains per device

Jean-Philippe Brucker
2019-02-13T11:55:31Z

Hi,

I have a few boring nits and one question below

On 13/02/2019 04:02, Lu Baolu wrote:
> Sharing a physical PCI device in a finer-granularity way
> is becoming a consensus in the industry. IOMMU vendors
> are also engaging efforts to support such sharing as well
> as possible. Among the efforts, the capability of support
> finer-granularity DMA isolation is a common requirement
> due to the security consideration. With finer-granularity
> DMA isolation, all DMA requests out of or to a subset of
> a physical PCI device can be protected by the IOMMU.

That last sentence seems strange, how about "With finer-granularity DMA
isolation, subsets of a PCI function can be isolated from each others by
the IOMMU."

> As a
> result, there is a request in software to attach multiple
> domains to a physical PCI device. One example of such use
> model is the Intel Scalable IOV [1] [2]. The Intel vt-d
> 3.0 spec [3] introduces the scalable mode which enables
> PASID granularity DMA isolation.
>
> This adds the APIs to support multiple domains per device.
> In order to ease the discussions, we call it 'a domain in
> auxiliary mode' or simply 'auxiliary domain' when multiple
> domains are attached to a physical device.
>
> The APIs include:
>
> * iommu_dev_has_feature(dev, IOMMU_DEV_FEAT_AUX)
>   - Check whether both IOMMU and device support IOMMU aux
>     domain feature. Below aux-domain specific interfaces
>     are available only after this returns true.

s/after/if/ since calling has_feature() shouldn't be a prerequisite to
using the aux-domain interface (unlike calling enable_feature()).

>
> * iommu_dev_enable/disable_feature(dev, IOMMU_DEV_FEAT_AUX)
>   - Enable/disable device specific aux-domain feature.
>
> * iommu_dev_feature_enabled(dev, IOMMU_DEV_FEAT_AUX)
>   - Check whether the aux domain specific feature enabled or
>     not.

"is enabled"

>
> * iommu_aux_attach_device(domain, dev)
>   - Attaches @domain to @dev in the auxiliary mode. Multiple
>     domains could be attached to a single device in the
>     auxiliary mode with each domain representing an isolated
>     address space for an assignable subset of the device.
>
> * iommu_aux_detach_device(domain, dev)
>   - Detach @domain which has been attached to @dev in the
>     auxiliary mode.
>
> * iommu_aux_get_pasid(domain, dev)
>   - Return ID used for finer-granularity DMA translation.
>     For the Intel Scalable IOV usage model, this will be
>     a PASID. The device which supports Scalable IOV needs
>     to write this ID to the device register so that DMA
>     requests could be tagged with a right PASID prefix.
>
> This has been updated with the latest proposal from Joerg
> posted here [5].
>
> Many people involved in discussions of this design.
>
> Kevin Tian <kevin.tian@intel.com>
> Liu Yi L <yi.l.liu@intel.com>
> Ashok Raj <ashok.raj@intel.com>
> Sanjay Kumar <sanjay.k.kumar@intel.com>
> Jacob Pan <jacob.jun.pan@linux.intel.com>
> Alex Williamson <alex.williamson@redhat.com>
> Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
> Joerg Roedel <joro@8bytes.org>
>
> and some discussions can be found here [4] [5].
>
> [1]
> https://software.intel.com/en-us/download/intel-scalable-io-virtualization-technical-specification
> [2] https://schd.ws/hosted_files/lc32018/00/LC3-SIOV-final.pdf
> [3]
> https://software.intel.com/en-us/download/intel-virtualization-technology-for-directed-io-architecture-specification
> [4] https://lkml.org/lkml/2018/7/26/4
> [5] https://www.spinics.net/lists/iommu/msg31874.html
>
> Cc: Ashok Raj <ashok.raj@intel.com>
> Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Cc: Kevin Tian <kevin.tian@intel.com>
> Cc: Liu Yi L <yi.l.liu@intel.com>
> Suggested-by: Kevin Tian <kevin.tian@intel.com>
> Suggested-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
> Suggested-by: Joerg Roedel <jroedel@suse.de>
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
>  drivers/iommu/iommu.c | 91 +++++++++++++++++++++++++++++++++++++++++++
>  include/linux/iommu.h | 70 +++++++++++++++++++++++++++++++++
>  2 files changed, 161 insertions(+)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 3ed4db334341..d0b323e8357f 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -2033,3 +2033,94 @@ int iommu_fwspec_add_ids(struct device *dev, u32
> *ids, int num_ids)
>          return 0;
>  }
>  EXPORT_SYMBOL_GPL(iommu_fwspec_add_ids);
> +
> +/*
> + * Per device IOMMU features.
> + */
> +bool iommu_dev_has_feature(struct device *dev, enum iommu_dev_features
> feat)
> +{
> +       const struct iommu_ops *ops = dev->bus->iommu_ops;
> +
> +       if (ops && ops->dev_has_feat)
> +               return ops->dev_has_feat(dev, feat);
> +
> +       return false;
> +}
> +EXPORT_SYMBOL_GPL(iommu_dev_has_feature);
> +
> +int iommu_dev_enable_feature(struct device *dev, enum
> iommu_dev_features feat)
> +{
> +       const struct iommu_ops *ops = dev->bus->iommu_ops;
> +
> +       if (ops && ops->dev_enable_feat)
> +               return ops->dev_enable_feat(dev, feat);
> +
> +       return -ENODEV;
> +}
> +EXPORT_SYMBOL_GPL(iommu_dev_enable_feature);
> +
> +int iommu_dev_disable_feature(struct device *dev, enum
> iommu_dev_features feat)
> +{
> +       const struct iommu_ops *ops = dev->bus->iommu_ops;
> +
> +       if (ops && ops->dev_disable_feat)
> +               return ops->dev_disable_feat(dev, feat);
> +
> +       return -ENODEV;
> +}
> +EXPORT_SYMBOL_GPL(iommu_dev_disable_feature);
> +
> +bool iommu_dev_feature_enabled(struct device *dev, enum
> iommu_dev_features feat)
> +{
> +       const struct iommu_ops *ops = dev->bus->iommu_ops;
> +
> +       if (ops && ops->dev_feat_enabled)
> +               return ops->dev_feat_enabled(dev, feat);
> +
> +       return false;
> +}
> +EXPORT_SYMBOL_GPL(iommu_dev_feature_enabled);
> +
> +/*
> + * Aux-domain specific attach/detach.
> + *
> + * Only works if iommu_dev_has_feature(dev, IOMMU_DEV_FEAT_AUX) returns
> true.

Rather "Only works if iommu_dev_feature_enabled(dev, AUX) returns true"?

> + * Also, as long as domains are attached to a device through this
> interface,
> + * any tries to call iommu_attach_device() should fail
> (iommu_detach_device()
> + * can't fail, so we fail on the tryint to re-attach). This should make

"when trying to re-attach"

> us safe
> + * against a device being attached to a guest as a whole while there
> are still
> + * pasid users on it (aux and sva).

A related question: is calling iommu_dev_disable_feat(dev, AUX) enough
to detach all auxiliary domains? I guess device drivers will always need
to tidy contexts up one by one, so maybe iommu_dev_disable_feat(dev,
AUX) can return -EBUSY in this case? I think we need to specify this in
a comment so device drivers know how to clean up.

Thanks,
Jean

> + */
> +int iommu_aux_attach_device(struct iommu_domain *domain, struct device
> *dev)
> +{
> +       int ret = -ENODEV;
> +
> +       if (domain->ops->aux_attach_dev)
> +               ret = domain->ops->aux_attach_dev(domain, dev);
> +
> +       if (!ret)
> +               trace_attach_device_to_domain(dev);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_aux_attach_device);
> +
> +void iommu_aux_detach_device(struct iommu_domain *domain, struct device
> *dev)
> +{
> +       if (domain->ops->aux_detach_dev) {
> +               domain->ops->aux_detach_dev(domain, dev);
> +               trace_detach_device_from_domain(dev);
> +       }
> +}
> +EXPORT_SYMBOL_GPL(iommu_aux_detach_device);
> +
> +int iommu_aux_get_pasid(struct iommu_domain *domain, struct device *dev)
> +{
> +       int ret = -ENODEV;
> +
> +       if (domain->ops->aux_get_pasid)
> +               ret = domain->ops->aux_get_pasid(domain, dev);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_aux_get_pasid);
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index e90da6b6f3d1..831eb29b35c5 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -156,6 +156,11 @@ struct iommu_resv_region {
>          enum iommu_resv_type    type;
>  };
>
> +/* Per device IOMMU features */
> +enum iommu_dev_features {
> +       IOMMU_DEV_FEAT_AUX,     /* Aux-domain feature */
> +};
> +
>  #ifdef CONFIG_IOMMU_API
>
>  /**
> @@ -183,6 +188,11 @@ struct iommu_resv_region {
>   * @domain_window_enable: Configure and enable a particular window for
> a domain
>   * @domain_window_disable: Disable a particular window for a domain
>   * @of_xlate: add OF master IDs to iommu grouping
> + * @dev_has/enable/disable_feat: per device entries to check/enable/disable
> + *                               iommu specific features.
> + * @dev_feat_enabled: check enabled feature
> + * @aux_attach/detach_dev: aux-domain specific attach/detach entries.
> + * @aux_get_pasid: get the pasid given an aux-domain
>   * @pgsize_bitmap: bitmap of all possible supported page sizes
>   */
>  struct iommu_ops {
> @@ -226,6 +236,17 @@ struct iommu_ops {
>          int (*of_xlate)(struct device *dev, struct of_phandle_args *args);
>          bool (*is_attach_deferred)(struct iommu_domain *domain, struct
> device *dev);
>
> +       /* Per device IOMMU features */
> +       bool (*dev_has_feat)(struct device *dev, enum iommu_dev_features f);
> +       bool (*dev_feat_enabled)(struct device *dev, enum
> iommu_dev_features f);
> +       int (*dev_enable_feat)(struct device *dev, enum
> iommu_dev_features f);
> +       int (*dev_disable_feat)(struct device *dev, enum
> iommu_dev_features f);
> +
> +       /* Aux-domain specific attach/detach entries */
> +       int (*aux_attach_dev)(struct iommu_domain *domain, struct device
> *dev);
> +       void (*aux_detach_dev)(struct iommu_domain *domain, struct
> device *dev);
> +       int (*aux_get_pasid)(struct iommu_domain *domain, struct device
> *dev);
> +
>          unsigned long pgsize_bitmap;
>  };
>
> @@ -412,6 +433,14 @@ static inline void dev_iommu_fwspec_set(struct
> device *dev,
>  int iommu_probe_device(struct device *dev);
>  void iommu_release_device(struct device *dev);
>
> +bool iommu_dev_has_feature(struct device *dev, enum iommu_dev_features f);
> +int iommu_dev_enable_feature(struct device *dev, enum
> iommu_dev_features f);
> +int iommu_dev_disable_feature(struct device *dev, enum
> iommu_dev_features f);
> +bool iommu_dev_feature_enabled(struct device *dev, enum
> iommu_dev_features f);
> +int iommu_aux_attach_device(struct iommu_domain *domain, struct device
> *dev);
> +void iommu_aux_detach_device(struct iommu_domain *domain, struct device
> *dev);
> +int iommu_aux_get_pasid(struct iommu_domain *domain, struct device *dev);
> +
>  #else /* CONFIG_IOMMU_API */
>
>  struct iommu_ops {};
> @@ -696,6 +725,47 @@ const struct iommu_ops
> *iommu_ops_from_fwnode(struct fwnode_handle *fwnode)
>          return NULL;
>  }
>
> +static inline bool
> +iommu_dev_has_feature(struct device *dev, enum iommu_dev_features feat)
> +{
> +       return false;
> +}
> +
> +static inline bool
> +iommu_dev_feature_enabled(struct device *dev, enum iommu_dev_features feat)
> +{
> +       return false;
> +}
> +
> +static inline int
> +iommu_dev_enable_feature(struct device *dev, enum iommu_dev_features feat)
> +{
> +       return -ENODEV;
> +}
> +
> +static inline int
> +iommu_dev_disable_feature(struct device *dev, enum iommu_dev_features feat)
> +{
> +       return -ENODEV;
> +}
> +
> +static inline int
> +iommu_aux_attach_device(struct iommu_domain *domain, struct device *dev)
> +{
> +       return -ENODEV;
> +}
> +
> +static inline void
> +iommu_aux_detach_device(struct iommu_domain *domain, struct device *dev)
> +{
> +}
> +
> +static inline int
> +iommu_aux_get_pasid(struct iommu_domain *domain, struct device *dev)
> +{
> +       return -ENODEV;
> +}
> +
>  #endif /* CONFIG_IOMMU_API */
>
>  #ifdef CONFIG_IOMMU_DEBUGFS
> --
> 2.17.1
>