Re: [RFC 5/9] iommu: Introduce fault notifier API

[Alex Williamson <alex.williamson-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Wed, 14 Jun 2017 15:22:59 -0700
Jacob Pan <jacob.jun.pan-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> wrote:

> Traditionally, device specific faults are detected and handled within
> their own device drivers. When IOMMU is enabled, faults such as DMA
> related transactions are detected by IOMMU. There is no generic
> reporting mechanism to report faults back to the in-kernel device
> driver or the guest OS in case of assigned devices.
> 
> Faults detected by IOMMU is based on the transaction's source ID which
> can be reported at per device basis, regardless of the device type is a
> PCI device or not.
> 
> The fault types includes recoverable (e.g. page request) and
> unrecoverable faults(e.g. invalid context). In most cases, faults can be
> handled by IOMMU drivers. However, there are use cases that require
> fault processing outside IOMMU driver, e.g.
> 
> 1. page request fault originated from an SVM capable device that is
> assigned to guest via vIOMMU. In this case, the first level page tables
> are owned by the guest. Page request must be propagated to the guest to
> let guest OS fault in the pages then send page response. In this
> mechanism, the direct receiver of IOMMU fault notification is VFIO,
> which can relay notification events to QEMU or other user space
> software.
> 
> 2. faults need more subtle handling by device drivers. Other than
> simply invoke reset function, there are needs to let device driver
> handle the fault with a smaller impact.
> 
> This patchset is intended to create a generic fault notification API such
> that it can scale as follows:
> - all IOMMU types
> - PCI and non-PCI devices
> - recoverable and unrecoverable faults
> - VFIO and other other in kernel users
> - DMA & IRQ remapping (TBD)
> 
> The event data contains both generic and raw architectural data
> such that performance is not compromised as the data propagation may
> involve many layers.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
> Signed-off-by: Ashok Raj <ashok.raj-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> ---
>  drivers/iommu/iommu.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/iommu.h | 54 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 117 insertions(+)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index c786370..04c73f3 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -48,6 +48,7 @@ struct iommu_group {
>  	struct list_head devices;
>  	struct mutex mutex;
>  	struct blocking_notifier_head notifier;
> +	struct blocking_notifier_head fault_notifier;
>  	void *iommu_data;
>  	void (*iommu_data_release)(void *iommu_data);
>  	char *name;
> @@ -345,6 +346,7 @@ struct iommu_group *iommu_group_alloc(void)
>  	mutex_init(&group->mutex);
>  	INIT_LIST_HEAD(&group->devices);
>  	BLOCKING_INIT_NOTIFIER_HEAD(&group->notifier);
> +	BLOCKING_INIT_NOTIFIER_HEAD(&group->fault_notifier);
>  
>  	ret = ida_simple_get(&iommu_group_ida, 0, 0, GFP_KERNEL);
>  	if (ret < 0) {
> @@ -790,6 +792,67 @@ int iommu_group_unregister_notifier(struct iommu_group *group,
>  EXPORT_SYMBOL_GPL(iommu_group_unregister_notifier);
>  
>  /**
> + * iommu_register_fault_notifier - Register a notifier for fault reporting
> + * @dev: device to notify fault events
> + * @nb: notifier block to signal
> + *
> + */
> +int iommu_register_fault_notifier(struct device *dev,
> +				struct notifier_block *nb)
> +{
> +	int ret;
> +	struct iommu_group *group = iommu_group_get(dev);
> +
> +	if (!group)
> +		return -EINVAL;
> +
> +	ret = blocking_notifier_chain_register(&group->fault_notifier, nb);
> +	iommu_group_put(group);
> +
> +	return ret;
> +
> +}
> +EXPORT_SYMBOL_GPL(iommu_register_fault_notifier);
> +
> +/**
> + * iommu_unregister_fault_notifier - Unregister a notifier for fault reporting
> + * @domain: the domain to watch
> + * @nb: notifier block to signal
> + *
> + */
> +int iommu_unregister_fault_notifier(struct device *dev,
> +				  struct notifier_block *nb)
> +{
> +	int ret;
> +	struct iommu_group *group = iommu_group_get(dev);
> +
> +	if (!group)
> +		return -EINVAL;
> +
> +	ret = blocking_notifier_chain_unregister(&group->fault_notifier, nb);
> +	iommu_group_put(group);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_unregister_fault_notifier);


If the call chains are on the group, why do we register with a device?
If I registered with a group, I'd know that I only need to register
once per group, that's not clear here and may lead to callers of this
getting multiple notifications, one for each device in a group.

> +
> +int iommu_fault_notifier_call_chain(struct iommu_fault_event *event)
> +{
> +	int ret;
> +	struct iommu_group *group = iommu_group_get(event->dev);
> +
> +	if (!group)
> +		return -EINVAL;
> +	/* caller provide generic data related to the event, TBD */
> +	ret = (blocking_notifier_call_chain(&group->fault_notifier, 0, (void *)event)
> +		== NOTIFY_BAD) ? -EINVAL : 0;
> +	iommu_group_put(group);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(iommu_fault_notifier_call_chain);
> +
> +/**
>   * iommu_group_id - Return ID for a group
>   * @group: the group to ID
>   *
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 2cdbaa3..fe89e88 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -42,6 +42,7 @@
>   * if the IOMMU page table format is equivalent.
>   */
>  #define IOMMU_PRIV	(1 << 5)
> +#define IOMMU_EXEC	(1 << 6)

Irrelevant change?

>  
>  struct iommu_ops;
>  struct iommu_group;
> @@ -97,6 +98,36 @@ struct iommu_domain {
>  	void *iova_cookie;
>  };
>  
> +/*
> + * Generic fault event notification data, used by all IOMMU architectures.
> + *
> + * - PCI and non-PCI devices
> + * - Recoverable faults (e.g. page request) & un-recoverable faults
> + * - DMA remapping and IRQ remapping faults
> + *
> + * @dev The device which faults are reported by IOMMU
> + * @addr tells the offending address
> + * @pasid contains process address space ID, used in shared virtual memory (SVM)
> + * @prot page access protection flag, e.g. IOMMU_READ, IOMMU_WRITE
> + * @flags contains fault type, etc.
> + * @length tells the size of the buf
> + * @buf contains any raw or arch specific data
> + *
> + */
> +struct iommu_fault_event {
> +	struct device *dev;
> +	__u64 addr;
> +	__u32 pasid;
> +	__u32 prot;
> +	__u32 flags;
> +#define IOMMU_FAULT_PAGE_REQ	BIT(0)
> +#define IOMMU_FAULT_UNRECOV	BIT(1)
> +#define IOMMU_FAULT_IRQ_REMAP	BIT(2)
> +#define IOMMU_FAULT_INVAL	BIT(3)

Details of each of these are defined where?

> +	__u32 length;
> +	__u8  buf[];
> +};

This is not UAPI, so I'll be curious how vfio is supposed to expose this
to userspace.

> +
>  enum iommu_cap {
>  	IOMMU_CAP_CACHE_COHERENCY,	/* IOMMU can enforce cache coherent DMA
>  					   transactions */
> @@ -341,6 +372,12 @@ extern int iommu_group_register_notifier(struct iommu_group *group,
>  					 struct notifier_block *nb);
>  extern int iommu_group_unregister_notifier(struct iommu_group *group,
>  					   struct notifier_block *nb);
> +extern int iommu_register_fault_notifier(struct device *dev,
> +					 struct notifier_block *nb);
> +extern int iommu_unregister_fault_notifier(struct device *dev,
> +					 struct notifier_block *nb);
> +extern int iommu_fault_notifier_call_chain(struct iommu_fault_event *event);
> +
>  extern int iommu_group_id(struct iommu_group *group);
>  extern struct iommu_group *iommu_group_get_for_dev(struct device *dev);
>  extern struct iommu_domain *iommu_group_default_domain(struct iommu_group *);
> @@ -573,6 +610,23 @@ static inline int iommu_group_unregister_notifier(struct iommu_group *group,
>  	return 0;
>  }
>  
> +static inline int iommu_register_fault_notifier(struct device *dev,
> +						  struct notifier_block *nb)
> +{
> +	return 0;
> +}
> +
> +static inline int iommu_unregister_fault_notifier(struct device *dev,
> +						  struct notifier_block *nb)
> +{
> +	return 0;
> +}
> +
> +static inline int iommu_fault_notifier_call_chain(struct iommu_fault_event *event)
> +{
> +	return 0;
> +}
> +
>  static inline int iommu_group_id(struct iommu_group *group)
>  {
>  	return -ENODEV;