Re: [PATCH v2 02/40] iommu/sva: Bind process address spaces to devices

Jonathan Cameron
2018-05-17T13:10:58Z

On Fri, 11 May 2018 20:06:03 +0100
Jean-Philippe Brucker <jean-philippe.brucker-5wv7dgnIgG8@public.gmane.org> wrote:

> Add bind() and unbind() operations to the IOMMU API. Bind() returns a
> PASID that drivers can program in hardware, to let their devices access an
> mm. This patch only adds skeletons for the device driver API, most of the
> implementation is still missing.
>
> IOMMU groups with more than one device aren't supported for SVA at the
> moment. There may be P2P traffic between devices within a group, which
> cannot be seen by an IOMMU (note that supporting PASID doesn't add any
> form of isolation with regard to P2P). Supporting groups would require
> calling bind() for all bound processes every time a device is added to a
> group, to perform sanity checks (e.g. ensure that new devices support
> PASIDs at least as big as those already allocated in the group).

Is it worth adding an explicit comment on this reasoning (or a minimal subset
of it) at the check for the number of devices in the group?
It's well laid out here, but might not be so obvious if someone is reading
the code in the future.

>It also
> means making sure that reserved ranges (IOMMU_RESV_*) of all devices are
> carved out of processes. This is already tricky with single devices, but
> becomes very difficult with groups. Since SVA-capable devices are expected
> to be cleanly isolated, and since we don't have any way to test groups or
> hot-plug, we only allow singular groups for now.
>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker-5wv7dgnIgG8@public.gmane.org>

Otherwise, looks good to me.

>
> ---
> v1->v2: remove iommu_sva_bind/unbind_group
> ---
> drivers/iommu/iommu-sva.c | 27 +++++++++++++
> drivers/iommu/iommu.c | 83 +++++++++++++++++++++++++++++++++++++++
> include/linux/iommu.h | 37 +++++++++++++++++
> 3 files changed, 147 insertions(+)
>
> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> index 8b4afb7c63ae..8d98f9c09864 100644
> --- a/drivers/iommu/iommu-sva.c
> +++ b/drivers/iommu/iommu-sva.c
> @@ -93,6 +93,8 @@ int iommu_sva_device_shutdown(struct device *dev)
> if (!domain)
> return -ENODEV;
>
> + __iommu_sva_unbind_dev_all(dev);
> +
> mutex_lock(&dev->iommu_param->lock);
> param = dev->iommu_param->sva_param;
> dev->iommu_param->sva_param = NULL;
> @@ -108,3 +110,28 @@ int iommu_sva_device_shutdown(struct device *dev)
> return 0;
> }
> EXPORT_SYMBOL_GPL(iommu_sva_device_shutdown);
> +
> +int __iommu_sva_bind_device(struct device *dev, struct mm_struct *mm,
> + int *pasid, unsigned long flags, void *drvdata)
> +{
> + return -ENOSYS; /* TODO */
> +}
> +EXPORT_SYMBOL_GPL(__iommu_sva_bind_device);
> +
> +int __iommu_sva_unbind_device(struct device *dev, int pasid)
> +{
> + return -ENOSYS; /* TODO */
> +}
> +EXPORT_SYMBOL_GPL(__iommu_sva_unbind_device);
> +
> +/**
> + * __iommu_sva_unbind_dev_all() - Detach all address spaces from this device
> + * @dev: the device
> + *
> + * When detaching @device from a domain, IOMMU drivers should use this helper.
> + */
> +void __iommu_sva_unbind_dev_all(struct device *dev)
> +{
> + /* TODO */
> +}
> +EXPORT_SYMBOL_GPL(__iommu_sva_unbind_dev_all);
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 9e28d88c8074..bd2819deae5b 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -2261,3 +2261,86 @@ int iommu_fwspec_add_ids(struct device *dev, u32 *ids, int num_ids)
> return 0;
> }
> EXPORT_SYMBOL_GPL(iommu_fwspec_add_ids);
> +
> +/**
> + * iommu_sva_bind_device() - Bind a process address space to a device
> + * @dev: the device
> + * @mm: the mm to bind, caller must hold a reference to it
> + * @pasid: valid address where the PASID will be stored
> + * @flags: bond properties
> + * @drvdata: private data passed to the mm exit handler
> + *
> + * Create a bond between device and task, allowing the device to access the mm
> + * using the returned PASID. If unbind() isn't called first, a subsequent bind()
> + * for the same device and mm fails with -EEXIST.
> + *
> + * iommu_sva_device_init() must be called first, to initialize the required SVA
> + * features. @flags is a subset of these features.
> + *
> + * The caller must pin down using get_user_pages*() all mappings shared with the
> + * device. mlock() isn't sufficient, as it doesn't prevent minor page faults
> + * (e.g. copy-on-write).
> + *
> + * On success, 0 is returned and @pasid contains a valid ID. Otherwise, an error
> + * is returned.
> + */
> +int iommu_sva_bind_device(struct device *dev, struct mm_struct *mm, int *pasid,
> + unsigned long flags, void *drvdata)
> +{
> + int ret = -EINVAL;
> + struct iommu_group *group;
> +
> + if (!pasid)
> + return -EINVAL;
> +
> + group = iommu_group_get(dev);
> + if (!group)
> + return -ENODEV;
> +
> + /* Ensure device count and domain don't change while we're binding */
> + mutex_lock(&group->mutex);
> + if (iommu_group_device_count(group) != 1)
> + goto out_unlock;
> +
> + ret = __iommu_sva_bind_device(dev, mm, pasid, flags, drvdata);
> +
> +out_unlock:
> + mutex_unlock(&group->mutex);
> + iommu_group_put(group);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_sva_bind_device);
> +
> +/**
> + * iommu_sva_unbind_device() - Remove a bond created with iommu_sva_bind_device
> + * @dev: the device
> + * @pasid: the pasid returned by bind()
> + *
> + * Remove bond between device and address space identified by @pasid. Users
> + * should not call unbind() if the corresponding mm exited (as the PASID might
> + * have been reallocated for another process).
> + *
> + * The device must not be issuing any more transaction for this PASID. All
> + * outstanding page requests for this PASID must have been flushed to the IOMMU.
> + *
> + * Returns 0 on success, or an error value
> + */
> +int iommu_sva_unbind_device(struct device *dev, int pasid)
> +{
> + int ret = -EINVAL;
> + struct iommu_group *group;
> +
> + group = iommu_group_get(dev);
> + if (!group)
> + return -ENODEV;
> +
> + mutex_lock(&group->mutex);
> + ret = __iommu_sva_unbind_device(dev, pasid);
> + mutex_unlock(&group->mutex);
> +
> + iommu_group_put(group);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_sva_unbind_device);
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 2efe7738bedb..da59c20c4f12 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -613,6 +613,10 @@ void iommu_fwspec_free(struct device *dev);
> int iommu_fwspec_add_ids(struct device *dev, u32 *ids, int num_ids);
> const struct iommu_ops *iommu_ops_from_fwnode(struct fwnode_handle *fwnode);
>
> +extern int iommu_sva_bind_device(struct device *dev, struct mm_struct *mm,
> + int *pasid, unsigned long flags, void *drvdata);
> +extern int iommu_sva_unbind_device(struct device *dev, int pasid);
> +
> #else /* CONFIG_IOMMU_API */
>
> struct iommu_ops {};
> @@ -932,12 +936,29 @@ static inline int iommu_sva_invalidate(struct iommu_domain *domain,
> return -EINVAL;
> }
>
> +static inline int iommu_sva_bind_device(struct device *dev,
> + struct mm_struct *mm, int *pasid,
> + unsigned long flags, void *drvdata)
> +{
> + return -ENODEV;
> +}
> +
> +static inline int iommu_sva_unbind_device(struct device *dev, int pasid)
> +{
> + return -ENODEV;
> +}
> +
> #endif /* CONFIG_IOMMU_API */
>
> #ifdef CONFIG_IOMMU_SVA
> extern int iommu_sva_device_init(struct device *dev, unsigned long features,
> unsigned int max_pasid);
> extern int iommu_sva_device_shutdown(struct device *dev);
> +extern int __iommu_sva_bind_device(struct device *dev, struct mm_struct *mm,
> + int *pasid, unsigned long flags,
> + void *drvdata);
> +extern int __iommu_sva_unbind_device(struct device *dev, int pasid);
> +extern void __iommu_sva_unbind_dev_all(struct device *dev);
> #else /* CONFIG_IOMMU_SVA */
> static inline int iommu_sva_device_init(struct device *dev,
> unsigned long features,
> @@ -950,6 +971,22 @@ static inline int iommu_sva_device_shutdown(struct device *dev)
> {
> return -ENODEV;
> }
> +
> +static inline int __iommu_sva_bind_device(struct device *dev,
> + struct mm_struct *mm, int *pasid,
> + unsigned long flags, void *drvdata)
> +{
> + return -ENODEV;
> +}
> +
> +static inline int __iommu_sva_unbind_device(struct device *dev, int pasid)
> +{
> + return -ENODEV;
> +}
> +
> +static inline void __iommu_sva_unbind_dev_all(struct device *dev)
> +{
> +}
> #endif /* CONFIG_IOMMU_SVA */
>
> #endif /* __LINUX_IOMMU_H */