Re: [PATCH v7 04/24] iommu: Add a page fault handler

Lu Baolu
2020-05-20T06:42:32Z

Hi Jean,

On 2020/5/20 1:54, Jean-Philippe Brucker wrote:
> Some systems allow devices to handle I/O Page Faults in the core mm. For
> example systems implementing the PCIe PRI extension or Arm SMMU stall
> model. Infrastructure for reporting these recoverable page faults was
> added to the IOMMU core by commit 0c830e6b3282 ("iommu: Introduce device
> fault report API"). 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@linaro.org>
> ---
> v6->v7: Fix leak in iopf_queue_discard_partial()
> ---
> drivers/iommu/Kconfig | 4 +
> drivers/iommu/Makefile | 1 +
> include/linux/iommu.h | 51 +++++
> drivers/iommu/io-pgfault.c | 459 +++++++++++++++++++++++++++++++++++++
> 4 files changed, 515 insertions(+)
> create mode 100644 drivers/iommu/io-pgfault.c
>
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index d9fa5b410015..15e9dc4e503c 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -107,6 +107,10 @@ config IOMMU_SVA
> bool
> select IOASID
>
> +config IOMMU_PAGE_FAULT
> + bool
> + select IOMMU_SVA
> +
> config FSL_PAMU
> bool "Freescale IOMMU support"
> depends on PCI
> diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
> index 40c800dd4e3e..bf5cb4ee8409 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-$(CONFIG_IOMMU_DEBUGFS) += iommu-debugfs.o
> obj-$(CONFIG_IOMMU_DMA) += dma-iommu.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

[SNIP]

> +
> +static enum iommu_page_response_code
> +iopf_handle_single(struct iopf_fault *iopf)
> +{
> + vm_fault_t ret;
> + struct mm_struct *mm;
> + struct vm_area_struct *vma;
> + unsigned int access_flags = 0;
> + unsigned int fault_flags = FAULT_FLAG_REMOTE;
> + struct iommu_fault_page_request *prm = &iopf->fault.prm;
> + enum iommu_page_response_code status = IOMMU_PAGE_RESP_INVALID;
> +
> + if (!(prm->flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID))
> + return status;
> +
> + mm = iommu_sva_find(prm->pasid);
> + if (IS_ERR_OR_NULL(mm))
> + return status;
> +
> + down_read(&mm->mmap_sem);
> +
> + vma = find_extend_vma(mm, prm->addr);
> + if (!vma)
> + /* Unmapped area */
> + goto out_put_mm;
> +
> + if (prm->perm & IOMMU_FAULT_PERM_READ)
> + access_flags |= VM_READ;
> +
> + if (prm->perm & IOMMU_FAULT_PERM_WRITE) {
> + access_flags |= VM_WRITE;
> + fault_flags |= FAULT_FLAG_WRITE;
> + }
> +
> + if (prm->perm & IOMMU_FAULT_PERM_EXEC) {
> + access_flags |= VM_EXEC;
> + fault_flags |= FAULT_FLAG_INSTRUCTION;
> + }
> +
> + if (!(prm->perm & IOMMU_FAULT_PERM_PRIV))
> + fault_flags |= FAULT_FLAG_USER;
> +
> + if (access_flags & ~vma->vm_flags)
> + /* Access fault */
> + goto out_put_mm;
> +
> + ret = handle_mm_fault(vma, prm->addr, fault_flags);
> + status = ret & VM_FAULT_ERROR ? IOMMU_PAGE_RESP_INVALID :

Do you mind telling why it's IOMMU_PAGE_RESP_INVALID but not
IOMMU_PAGE_RESP_FAILURE?

> + IOMMU_PAGE_RESP_SUCCESS;
> +
> +out_put_mm:
> + up_read(&mm->mmap_sem);
> + mmput(mm);
> +
> + return status;
> +}
> +
> +static void iopf_handle_group(struct work_struct *work)
> +{
> + struct iopf_group *group;
> + struct iopf_fault *iopf, *next;
> + enum iommu_page_response_code status = IOMMU_PAGE_RESP_SUCCESS;
> +
> + group = container_of(work, struct iopf_group, work);
> +
> + list_for_each_entry_safe(iopf, next, &group->faults, list) {
> + /*
> + * For the moment, errors are sticky: don't handle subsequent
> + * faults in the group if there is an error.
> + */
> + if (status == IOMMU_PAGE_RESP_SUCCESS)
> + status = iopf_handle_single(iopf);
> +
> + if (!(iopf->fault.prm.flags &
> + IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE))
> + kfree(iopf);
> + }
> +
> + iopf_complete_group(group->dev, &group->last_fault, status);
> + kfree(group);
> +}
> +
> +/**
> + * iommu_queue_iopf - IO Page Fault handler
> + * @evt: fault event

@fault?

> + * @cookie: struct device, passed to iommu_register_device_fault_handler.
> + *
> + * Add a fault to the device workqueue, to be handled by mm.
> + *
> + * This module doesn't handle PCI PASID Stop Marker; IOMMU drivers must discard
> + * them before reporting faults. A PASID Stop Marker (LRW = 0b100) doesn't
> + * expect a response. It may be generated when disabling a PASID (issuing a
> + * PASID stop request) by some PCI devices.
> + *
> + * The PASID stop request is issued by the device driver before unbind(). Once
> + * it completes, no page request is generated for this PASID anymore and
> + * outstanding ones have been pushed to the IOMMU (as per PCIe 4.0r1.0 - 6.20.1
> + * and 10.4.1.2 - Managing PASID TLP Prefix Usage). Some PCI devices will wait
> + * for all outstanding page requests to come back with a response before
> + * completing the PASID stop request. Others do not wait for page responses, and
> + * instead issue this Stop Marker that tells us when the PASID can be
> + * reallocated.
> + *
> + * It is safe to discard the Stop Marker because it is an optimization.
> + * a. Page requests, which are posted requests, have been flushed to the IOMMU
> + * when the stop request completes.
> + * b. We flush all fault queues on unbind() before freeing the PASID.
> + *
> + * So even though the Stop Marker might be issued by the device *after* the stop
> + * request completes, outstanding faults will have been dealt with by the time
> + * we free the PASID.
> + *
> + * Return: 0 on success and <0 on error.
> + */
> +int iommu_queue_iopf(struct iommu_fault *fault, void *cookie)
> +{
> + int ret;
> + struct iopf_group *group;
> + struct iopf_fault *iopf, *next;
> + struct iopf_device_param *iopf_param;
> +
> + struct device *dev = cookie;
> + struct dev_iommu *param = dev->iommu;
> +
> + lockdep_assert_held(&param->lock);
> +
> + if (fault->type != IOMMU_FAULT_PAGE_REQ)
> + /* Not a recoverable page fault */
> + return -EOPNOTSUPP;
> +
> + /*
> + * 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 (!(fault->prm.flags & IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE)) {
> + iopf = kzalloc(sizeof(*iopf), GFP_KERNEL);
> + if (!iopf)
> + return -ENOMEM;
> +
> + iopf->fault = *fault;
> +
> + /* Non-last request of a group. Postpone until the last one */
> + list_add(&iopf->list, &iopf_param->partial);
> +
> + return 0;
> + }
> +
> + group = kzalloc(sizeof(*group), GFP_KERNEL);
> + if (!group) {
> + /*
> + * The caller will send a response to the hardware. But we do
> + * need to clean up before leaving, otherwise partial faults
> + * will be stuck.
> + */
> + ret = -ENOMEM;
> + goto cleanup_partial;
> + }
> +
> + group->dev = dev;
> + group->last_fault.fault = *fault;
> + INIT_LIST_HEAD(&group->faults);
> + list_add(&group->last_fault.list, &group->faults);
> + INIT_WORK(&group->work, iopf_handle_group);
> +
> + /* See if we have partial faults for this group */
> + list_for_each_entry_safe(iopf, next, &iopf_param->partial, list) {
> + if (iopf->fault.prm.grpid == fault->prm.grpid)
> + /* Insert *before* the last fault */
> + list_move(&iopf->list, &group->faults);
> + }
> +
> + queue_work(iopf_param->queue->wq, &group->work);
> + return 0;
> +
> +cleanup_partial:
> + list_for_each_entry_safe(iopf, next, &iopf_param->partial, list) {
> + if (iopf->fault.prm.grpid == fault->prm.grpid) {
> + list_del(&iopf->list);
> + kfree(iopf);
> + }
> + }
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_queue_iopf);

[SNIP]

> +
> +
> +/**
> + * iopf_queue_add_device - Add producer to the fault queue
> + * @queue: IOPF queue
> + * @dev: device to add
> + *
> + * Return: 0 on success and <0 on error.
> + */
> +int iopf_queue_add_device(struct iopf_queue *queue, struct device *dev)
> +{
> + int ret = -EBUSY;
> + struct iopf_device_param *iopf_param;
> + struct dev_iommu *param = dev->iommu;
> +
> + 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; iopf_param->dev = dev;

Two lines?

> +
> + mutex_lock(&queue->lock);
> + mutex_lock(&param->lock);
> + if (!param->iopf_param) {
> + list_add(&iopf_param->queue_list, &queue->devices);
> + param->iopf_param = iopf_param;
> + ret = 0;
> + }
> + mutex_unlock(&param->lock);
> + mutex_unlock(&queue->lock);
> +
> + if (ret)
> + kfree(iopf_param);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(iopf_queue_add_device);
> +

[SNIP]
Best regards,
baolu