Re: [PATCH v2 07/40] iommu: Add a page fault handler

[Jacob Pan <jacob.jun.pan-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>]

On Fri, 11 May 2018 20:06:08 +0100
Jean-Philippe Brucker <jean-philippe.brucker-5wv7dgnIgG8@public.gmane.org> wrote:

> Some systems allow devices to handle I/O Page Faults in the core mm.
> For example systems implementing the PCI PRI extension or Arm SMMU
> stall model. Infrastructure for reporting these recoverable page
> faults was recently added to the IOMMU core for SVA virtualisation.
> Add a page fault handler for host SVA.
> 
> IOMMU driver can now instantiate several fault workqueues and link
> them to IOPF-capable devices. Drivers can choose between a single
> global workqueue, one per IOMMU device, one per low-level fault
> queue, one per domain, etc.
> 
> When it receives a fault event, supposedly in an IRQ handler, the
> IOMMU driver reports the fault using iommu_report_device_fault(),
> which calls the registered handler. The page fault handler then calls
> the mm fault handler, and reports either success or failure with
> iommu_page_response(). When the handler succeeded, the IOMMU retries
> the access.
> 
> The iopf_param pointer could be embedded into iommu_fault_param. But
> putting iopf_param into the iommu_param structure allows us not to
> care about ordering between calls to iopf_queue_add_device() and
> iommu_register_device_fault_handler().
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker-5wv7dgnIgG8@public.gmane.org>
> 
> ---
> v1->v2: multiple queues registered by IOMMU driver
> ---
>  drivers/iommu/Kconfig      |   4 +
>  drivers/iommu/Makefile     |   1 +
>  drivers/iommu/io-pgfault.c | 363
> +++++++++++++++++++++++++++++++++++++ include/linux/iommu.h      |
> 58 ++++++ 4 files changed, 426 insertions(+)
>  create mode 100644 drivers/iommu/io-pgfault.c
> 
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 38434899e283..09f13a7c4b60 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -79,6 +79,10 @@ config IOMMU_SVA
>  	select IOMMU_API
>  	select MMU_NOTIFIER
>  
> +config IOMMU_PAGE_FAULT
> +	bool
> +	select IOMMU_API
> +
>  config FSL_PAMU
>  	bool "Freescale IOMMU support"
>  	depends on PCI
> diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
> index 1dbcc89ebe4c..4b744e399a1b 100644
> --- a/drivers/iommu/Makefile
> +++ b/drivers/iommu/Makefile
> @@ -4,6 +4,7 @@ obj-$(CONFIG_IOMMU_API) += iommu-traces.o
>  obj-$(CONFIG_IOMMU_API) += iommu-sysfs.o
>  obj-$(CONFIG_IOMMU_DMA) += dma-iommu.o
>  obj-$(CONFIG_IOMMU_SVA) += iommu-sva.o
> +obj-$(CONFIG_IOMMU_PAGE_FAULT) += io-pgfault.o
>  obj-$(CONFIG_IOMMU_IO_PGTABLE) += io-pgtable.o
>  obj-$(CONFIG_IOMMU_IO_PGTABLE_ARMV7S) += io-pgtable-arm-v7s.o
>  obj-$(CONFIG_IOMMU_IO_PGTABLE_LPAE) += io-pgtable-arm.o
> diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
> new file mode 100644
> index 000000000000..321c00dd3a3d
> --- /dev/null
> +++ b/drivers/iommu/io-pgfault.c
> @@ -0,0 +1,363 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Handle device page faults
> + *
> + * Copyright (C) 2018 ARM Ltd.
> + */
> +
> +#include <linux/iommu.h>
> +#include <linux/list.h>
> +#include <linux/slab.h>
> +#include <linux/workqueue.h>
> +
> +/**
> + * struct iopf_queue - IO Page Fault queue
> + * @wq: the fault workqueue
> + * @flush: low-level flush callback
> + * @flush_arg: flush() argument
> + * @refs: references to this structure taken by producers
> + */
> +struct iopf_queue {
> +	struct workqueue_struct		*wq;
> +	iopf_queue_flush_t		flush;
> +	void				*flush_arg;
> +	refcount_t			refs;
> +};
> +
> +/**
> + * struct iopf_device_param - IO Page Fault data attached to a device
> + * @queue: IOPF queue
> + * @partial: faults that are part of a Page Request Group for which
> the last
> + *           request hasn't been submitted yet.
> + */
> +struct iopf_device_param {
> +	struct iopf_queue		*queue;
> +	struct list_head		partial;
> +};
> +
> +struct iopf_context {
> +	struct device			*dev;
> +	struct iommu_fault_event	evt;
> +	struct list_head		head;
> +};
> +
> +struct iopf_group {
> +	struct iopf_context		last_fault;
> +	struct list_head		faults;
> +	struct work_struct		work;
> +};
> +
All the page requests in the group should belong to the same device,
perhaps struct device tracking should be in iopf_group instead of
iopf_context?

> +static int iopf_complete(struct device *dev, struct
> iommu_fault_event *evt,
> +			 enum page_response_code status)
> +{
> +	struct page_response_msg resp = {
> +		.addr			= evt->addr,
> +		.pasid			= evt->pasid,
> +		.pasid_present		= evt->pasid_valid,
> +		.page_req_group_id	= evt->page_req_group_id,
> +		.private_data		= evt->iommu_private,
> +		.resp_code		= status,
> +	};
> +
> +	return iommu_page_response(dev, &resp);
> +}
> +
> +static enum page_response_code
> +iopf_handle_single(struct iopf_context *fault)
> +{
> +	/* TODO */
> +	return -ENODEV;
> +}
> +
> +static void iopf_handle_group(struct work_struct *work)
> +{
> +	struct iopf_group *group;
> +	struct iopf_context *fault, *next;
> +	enum page_response_code status = IOMMU_PAGE_RESP_SUCCESS;
> +
> +	group = container_of(work, struct iopf_group, work);
> +
> +	list_for_each_entry_safe(fault, next, &group->faults, head) {
> +		struct iommu_fault_event *evt = &fault->evt;
> +		/*
> +		 * Errors are sticky: don't handle subsequent faults
> in the
> +		 * group if there is an error.
> +		 */
There might be performance benefit for certain device to continue in
spite of error in that the ATS retry may have less fault. Perhaps a
policy decision for later enhancement.
> +		if (status == IOMMU_PAGE_RESP_SUCCESS)
> +			status = iopf_handle_single(fault);
> +
> +		if (!evt->last_req)
> +			kfree(fault);
> +	}
> +
> +	iopf_complete(group->last_fault.dev, &group->last_fault.evt,
> status);
> +	kfree(group);
> +}
> +
> +/**
> + * iommu_queue_iopf - IO Page Fault handler
> + * @evt: fault event
> + * @cookie: struct device, passed to
> iommu_register_device_fault_handler.
> + *
> + * Add a fault to the device workqueue, to be handled by mm.
> + */
> +int iommu_queue_iopf(struct iommu_fault_event *evt, void *cookie)
> +{
> +	struct iopf_group *group;
> +	struct iopf_context *fault, *next;
> +	struct iopf_device_param *iopf_param;
> +
> +	struct device *dev = cookie;
> +	struct iommu_param *param = dev->iommu_param;
> +
> +	if (WARN_ON(!mutex_is_locked(&param->lock)))
> +		return -EINVAL;
> +
> +	if (evt->type != IOMMU_FAULT_PAGE_REQ)
> +		/* Not a recoverable page fault */
> +		return IOMMU_PAGE_RESP_CONTINUE;
> +
> +	/*
> +	 * As long as we're holding param->lock, the queue can't be
> unlinked
> +	 * from the device and therefore cannot disappear.
> +	 */
> +	iopf_param = param->iopf_param;
> +	if (!iopf_param)
> +		return -ENODEV;
> +
> +	if (!evt->last_req) {
> +		fault = kzalloc(sizeof(*fault), GFP_KERNEL);
> +		if (!fault)
> +			return -ENOMEM;
> +
> +		fault->evt = *evt;
> +		fault->dev = dev;
> +
> +		/* Non-last request of a group. Postpone until the
> last one */
> +		list_add(&fault->head, &iopf_param->partial);
> +
> +		return IOMMU_PAGE_RESP_HANDLED;
> +	}
> +
> +	group = kzalloc(sizeof(*group), GFP_KERNEL);
> +	if (!group)
> +		return -ENOMEM;
> +
> +	group->last_fault.evt = *evt;
> +	group->last_fault.dev = dev;
> +	INIT_LIST_HEAD(&group->faults);
> +	list_add(&group->last_fault.head, &group->faults);
> +	INIT_WORK(&group->work, iopf_handle_group);
> +
> +	/* See if we have partial faults for this group */
> +	list_for_each_entry_safe(fault, next, &iopf_param->partial,
> head) {
> +		if (fault->evt.page_req_group_id ==
> evt->page_req_group_id)
If all 9 bit group index are used, there can be lots of PRGs. For
future enhancement, maybe we can have per group partial list ready to
go when LPIG comes in? I will be less searching.
> +			/* Insert *before* the last fault */
> +			list_move(&fault->head, &group->faults);
> +	}
> +
If you already sorted the group list with last fault at the end, why do
you need a separate entry to track the last fault?
> +	queue_work(iopf_param->queue->wq, &group->work);
> +
> +	/* Postpone the fault completion */
> +	return IOMMU_PAGE_RESP_HANDLED;
> +}
> +EXPORT_SYMBOL_GPL(iommu_queue_iopf);
> +
> +/**
> + * iopf_queue_flush_dev - Ensure that all queued faults have been
> processed
> + * @dev: the endpoint whose faults need to be flushed.
> + *
> + * Users must call this function when releasing a PASID, to ensure
> that all
> + * pending faults for this PASID have been handled, and won't hit
> the address
> + * space of the next process that uses this PASID.
> + *
> + * Return 0 on success.
> + */
> +int iopf_queue_flush_dev(struct device *dev)
> +{
> +	int ret = 0;
> +	struct iopf_queue *queue;
> +	struct iommu_param *param = dev->iommu_param;
> +
> +	if (!param)
> +		return -ENODEV;
> +
> +	/*
> +	 * It is incredibly easy to find ourselves in a deadlock
> situation if
> +	 * we're not careful, because we're taking the opposite path
> as
> +	 * iommu_queue_iopf:
> +	 *
> +	 *   iopf_queue_flush_dev()   |  PRI queue handler
> +	 *    lock(mutex)             |   iommu_queue_iopf()
> +	 *     queue->flush()         |    lock(mutex)
> +	 *      wait PRI queue empty  |
> +	 *
> +	 * So we can't hold the device param lock while flushing. We
> don't have
> +	 * to, because the queue or the device won't disappear until
> all flush
> +	 * are finished.
> +	 */
> +	mutex_lock(&param->lock);
> +	if (param->iopf_param) {
> +		queue = param->iopf_param->queue;
> +	} else {
> +		ret = -ENODEV;
> +	}
> +	mutex_unlock(&param->lock);
> +	if (ret)
> +		return ret;
> +
> +	queue->flush(queue->flush_arg, dev);
> +
> +	/*
> +	 * No need to clear the partial list. All PRGs containing
> the PASID that
> +	 * needs to be decommissioned are whole (the device driver
> made sure of
> +	 * it before this function was called). They have been
> submitted to the
> +	 * queue by the above flush().
> +	 */
So you are saying device driver need to make sure LPIG PRQ is submitted
in the flush call above such that partial list is cleared? what if
there are device failures where device needs to reset (either whole
function level or PASID level), should there still be a need to clear
the partial list for all associated PASID/group?
> +	flush_workqueue(queue->wq);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(iopf_queue_flush_dev);
> +
> +/**
> + * iopf_queue_add_device - Add producer to the fault queue
> + * @queue: IOPF queue
> + * @dev: device to add
> + */
> +int iopf_queue_add_device(struct iopf_queue *queue, struct device
> *dev) +{
> +	int ret = -EINVAL;
> +	struct iopf_device_param *iopf_param;
> +	struct iommu_param *param = dev->iommu_param;
> +
> +	if (!param)
> +		return -ENODEV;
> +
> +	iopf_param = kzalloc(sizeof(*iopf_param), GFP_KERNEL);
> +	if (!iopf_param)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&iopf_param->partial);
> +	iopf_param->queue = queue;
> +
> +	mutex_lock(&param->lock);
> +	if (!param->iopf_param) {
> +		refcount_inc(&queue->refs);
> +		param->iopf_param = iopf_param;
> +		ret = 0;
> +	}
> +	mutex_unlock(&param->lock);
> +
> +	if (ret)
> +		kfree(iopf_param);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(iopf_queue_add_device);
> +
> +/**
> + * iopf_queue_remove_device - Remove producer from fault queue
> + * @dev: device to remove
> + *
> + * Caller makes sure that no more fault is reported for this device,
> and no more
> + * flush is scheduled for this device.
> + *
> + * Note: safe to call unconditionally on a cleanup path, even if the
> device
> + * isn't registered to any IOPF queue.
> + *
> + * Return 0 if the device was attached to the IOPF queue
> + */
> +int iopf_queue_remove_device(struct device *dev)
> +{
> +	struct iopf_context *fault, *next;
> +	struct iopf_device_param *iopf_param;
> +	struct iommu_param *param = dev->iommu_param;
> +
> +	if (!param)
> +		return -EINVAL;
> +
> +	mutex_lock(&param->lock);
> +	iopf_param = param->iopf_param;
> +	if (iopf_param) {
> +		refcount_dec(&iopf_param->queue->refs);
> +		param->iopf_param = NULL;
> +	}
> +	mutex_unlock(&param->lock);
> +	if (!iopf_param)
> +		return -EINVAL;
> +
> +	list_for_each_entry_safe(fault, next, &iopf_param->partial,
> head)
> +		kfree(fault);
> +
> +	/*
> +	 * No more flush is scheduled, and the caller removed all
> bonds from
> +	 * this device. unbind() waited until any concurrent
> mm_exit() finished,
> +	 * therefore there is no flush() running anymore and we can
> free the
> +	 * param.
> +	 */
> +	kfree(iopf_param);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(iopf_queue_remove_device);
> +
> +/**
> + * iopf_queue_alloc - Allocate and initialize a fault queue
> + * @name: a unique string identifying the queue (for workqueue)
> + * @flush: a callback that flushes the low-level queue
> + * @cookie: driver-private data passed to the flush callback
> + *
> + * The callback is called before the workqueue is flushed. The IOMMU
> driver must
> + * commit all faults that are pending in its low-level queues at the
> time of the
> + * call, into the IOPF queue (with iommu_report_device_fault). The
> callback
> + * takes a device pointer as argument, hinting what endpoint is
> causing the
> + * flush. When the device is NULL, all faults should be committed.
> + */
> +struct iopf_queue *
> +iopf_queue_alloc(const char *name, iopf_queue_flush_t flush, void
> *cookie) +{
> +	struct iopf_queue *queue;
> +
> +	queue = kzalloc(sizeof(*queue), GFP_KERNEL);
> +	if (!queue)
> +		return NULL;
> +
> +	/*
> +	 * The WQ is unordered because the low-level handler
> enqueues faults by
> +	 * group. PRI requests within a group have to be ordered,
> but once
> +	 * that's dealt with, the high-level function can handle
> groups out of
> +	 * order.
> +	 */
> +	queue->wq = alloc_workqueue("iopf_queue/%s", WQ_UNBOUND, 0,
> name);
> +	if (!queue->wq) {
> +		kfree(queue);
> +		return NULL;
> +	}
> +
> +	queue->flush = flush;
> +	queue->flush_arg = cookie;
> +	refcount_set(&queue->refs, 1);
> +
> +	return queue;
> +}
> +EXPORT_SYMBOL_GPL(iopf_queue_alloc);
> +
> +/**
> + * iopf_queue_free - Free IOPF queue
> + * @queue: queue to free
> + *
> + * Counterpart to iopf_queue_alloc(). Caller must make sure that all
> producers
> + * have been removed.
> + */
> +void iopf_queue_free(struct iopf_queue *queue)
> +{
> +
> +	/* Caller should have removed all producers first */
> +	if (WARN_ON(!refcount_dec_and_test(&queue->refs)))
> +		return;
> +
> +	destroy_workqueue(queue->wq);
> +	kfree(queue);
> +}
> +EXPORT_SYMBOL_GPL(iopf_queue_free);
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index faf3390ce89d..fad3a60e1c14 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -461,11 +461,20 @@ struct iommu_fault_param {
>  	void *data;
>  };
>  
> +/**
> + * iopf_queue_flush_t - Flush low-level page fault queue
> + *
> + * Report all faults currently pending in the low-level page fault
> queue
> + */
> +struct iopf_queue;
> +typedef int (*iopf_queue_flush_t)(void *cookie, struct device *dev);
> +
>  /**
>   * struct iommu_param - collection of per-device IOMMU data
>   *
>   * @fault_param: IOMMU detected device fault reporting data
>   * @sva_param: SVA parameters
> + * @iopf_param: I/O Page Fault queue and data
>   *
>   * TODO: migrate other per device data pointers under
> iommu_dev_data, e.g.
>   *	struct iommu_group	*iommu_group;
> @@ -475,6 +484,7 @@ struct iommu_param {
>  	struct mutex lock;
>  	struct iommu_fault_param *fault_param;
>  	struct iommu_sva_param *sva_param;
> +	struct iopf_device_param *iopf_param;
>  };
>  
>  int  iommu_device_register(struct iommu_device *iommu);
> @@ -874,6 +884,12 @@ static inline int
> iommu_report_device_fault(struct device *dev, struct iommu_fau return
> 0; }
>  
> +static inline int iommu_page_response(struct device *dev,
> +				      struct page_response_msg *msg)
> +{
> +	return -ENODEV;
> +}
> +
>  static inline int iommu_group_id(struct iommu_group *group)
>  {
>  	return -ENODEV;
> @@ -1038,4 +1054,46 @@ static inline struct mm_struct
> *iommu_sva_find(int pasid) }
>  #endif /* CONFIG_IOMMU_SVA */
>  
> +#ifdef CONFIG_IOMMU_PAGE_FAULT
> +extern int iommu_queue_iopf(struct iommu_fault_event *evt, void
> *cookie); +
> +extern int iopf_queue_add_device(struct iopf_queue *queue, struct
> device *dev); +extern int iopf_queue_remove_device(struct device
> *dev); +extern int iopf_queue_flush_dev(struct device *dev);
> +extern struct iopf_queue *
> +iopf_queue_alloc(const char *name, iopf_queue_flush_t flush, void
> *cookie); +extern void iopf_queue_free(struct iopf_queue *queue);
> +#else /* CONFIG_IOMMU_PAGE_FAULT */
> +static inline int iommu_queue_iopf(struct iommu_fault_event *evt,
> void *cookie) +{
> +	return -ENODEV;
> +}
> +
> +static inline int iopf_queue_add_device(struct iopf_queue *queue,
> +					struct device *dev)
> +{
> +	return -ENODEV;
> +}
> +
> +static inline int iopf_queue_remove_device(struct device *dev)
> +{
> +	return -ENODEV;
> +}
> +
> +static inline int iopf_queue_flush_dev(struct device *dev)
> +{
> +	return -ENODEV;
> +}
> +
> +static inline struct iopf_queue *
> +iopf_queue_alloc(const char *name, iopf_queue_flush_t flush, void
> *cookie) +{
> +	return NULL;
> +}
> +
> +static inline void iopf_queue_free(struct iopf_queue *queue)
> +{
> +}
> +#endif /* CONFIG_IOMMU_PAGE_FAULT */
> +
>  #endif /* __LINUX_IOMMU_H */