Re: [RFC PATCH v3 8/8] vfio: Add nested IOPF support

[Shenming Lu]

On 2021/5/19 2:58, Alex Williamson wrote:
> On Fri, 9 Apr 2021 11:44:20 +0800
> Shenming Lu <lushenming@xxxxxxxxxx> wrote:
> 
>> To set up nested mode, drivers such as vfio_pci need to register a
>> handler to receive stage/level 1 faults from the IOMMU, but since
>> currently each device can only have one iommu dev fault handler,
>> and if stage 2 IOPF is already enabled (VFIO_IOMMU_ENABLE_IOPF),
>> we choose to update the registered handler (a consolidated one) via
>> flags (set FAULT_REPORT_NESTED_L1), and further deliver the received
>> stage 1 faults in the handler to the guest through a newly added
>> vfio_device_ops callback.
> 
> Are there proposed in-kernel drivers that would use any of these
> symbols?

I hope that such as Eric's SMMUv3 Nested Stage Setup series [1] can
use these symbols to consolidate the two page fault handlers into one.

[1] https://patchwork.kernel.org/project/kvm/cover/20210411114659.15051-1-eric.auger@xxxxxxxxxx/

> 
>> Signed-off-by: Shenming Lu <lushenming@xxxxxxxxxx>
>> ---
>>  drivers/vfio/vfio.c             | 81 +++++++++++++++++++++++++++++++++
>>  drivers/vfio/vfio_iommu_type1.c | 49 +++++++++++++++++++-
>>  include/linux/vfio.h            | 12 +++++
>>  3 files changed, 141 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
>> index 44c8dfabf7de..4245f15914bf 100644
>> --- a/drivers/vfio/vfio.c
>> +++ b/drivers/vfio/vfio.c
>> @@ -2356,6 +2356,87 @@ struct iommu_domain *vfio_group_iommu_domain(struct vfio_group *group)
>>  }
>>  EXPORT_SYMBOL_GPL(vfio_group_iommu_domain);
>>  
>> +/*
>> + * Register/Update the VFIO IOPF handler to receive
>> + * nested stage/level 1 faults.
>> + */
>> +int vfio_iommu_dev_fault_handler_register_nested(struct device *dev)
>> +{
>> +	struct vfio_container *container;
>> +	struct vfio_group *group;
>> +	struct vfio_iommu_driver *driver;
>> +	int ret;
>> +
>> +	if (!dev)
>> +		return -EINVAL;
>> +
>> +	group = vfio_group_get_from_dev(dev);
>> +	if (!group)
>> +		return -ENODEV;
>> +
>> +	ret = vfio_group_add_container_user(group);
>> +	if (ret)
>> +		goto out;
>> +
>> +	container = group->container;
>> +	driver = container->iommu_driver;
>> +	if (likely(driver && driver->ops->register_handler))
>> +		ret = driver->ops->register_handler(container->iommu_data, dev);
>> +	else
>> +		ret = -ENOTTY;
>> +
>> +	vfio_group_try_dissolve_container(group);
>> +
>> +out:
>> +	vfio_group_put(group);
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(vfio_iommu_dev_fault_handler_register_nested);
>> +
>> +int vfio_iommu_dev_fault_handler_unregister_nested(struct device *dev)
>> +{
>> +	struct vfio_container *container;
>> +	struct vfio_group *group;
>> +	struct vfio_iommu_driver *driver;
>> +	int ret;
>> +
>> +	if (!dev)
>> +		return -EINVAL;
>> +
>> +	group = vfio_group_get_from_dev(dev);
>> +	if (!group)
>> +		return -ENODEV;
>> +
>> +	ret = vfio_group_add_container_user(group);
>> +	if (ret)
>> +		goto out;
>> +
>> +	container = group->container;
>> +	driver = container->iommu_driver;
>> +	if (likely(driver && driver->ops->unregister_handler))
>> +		ret = driver->ops->unregister_handler(container->iommu_data, dev);
>> +	else
>> +		ret = -ENOTTY;
>> +
>> +	vfio_group_try_dissolve_container(group);
>> +
>> +out:
>> +	vfio_group_put(group);
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(vfio_iommu_dev_fault_handler_unregister_nested);
>> +
>> +int vfio_transfer_iommu_fault(struct device *dev, struct iommu_fault *fault)
>> +{
>> +	struct vfio_device *device = dev_get_drvdata(dev);
>> +
>> +	if (unlikely(!device->ops->transfer))
>> +		return -EOPNOTSUPP;
>> +
>> +	return device->ops->transfer(device->device_data, fault);
>> +}
>> +EXPORT_SYMBOL_GPL(vfio_transfer_iommu_fault);
>> +
>>  /**
>>   * Module/class support
>>   */
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index ba2b5a1cf6e9..9d1adeddb303 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -3821,13 +3821,32 @@ static int vfio_iommu_type1_dma_map_iopf(struct iommu_fault *fault, void *data)
>>  	struct vfio_batch batch;
>>  	struct vfio_range *range;
>>  	dma_addr_t iova = ALIGN_DOWN(fault->prm.addr, PAGE_SIZE);
>> -	int access_flags = 0;
>> +	int access_flags = 0, nested;
>>  	size_t premap_len, map_len, mapped_len = 0;
>>  	unsigned long bit_offset, vaddr, pfn, i, npages;
>>  	int ret;
>>  	enum iommu_page_response_code status = IOMMU_PAGE_RESP_INVALID;
>>  	struct iommu_page_response resp = {0};
>>  
>> +	if (vfio_dev_domian_nested(dev, &nested))
>> +		return -ENODEV;
>> +
>> +	/*
>> +	 * When configured in nested mode, further deliver the
>> +	 * stage/level 1 faults to the guest.
>> +	 */
>> +	if (nested) {
>> +		bool l2;
>> +
>> +		if (fault->type == IOMMU_FAULT_PAGE_REQ)
>> +			l2 = fault->prm.flags & IOMMU_FAULT_PAGE_REQUEST_L2;
>> +		if (fault->type == IOMMU_FAULT_DMA_UNRECOV)
>> +			l2 = fault->event.flags & IOMMU_FAULT_UNRECOV_L2;
>> +
>> +		if (!l2)
>> +			return vfio_transfer_iommu_fault(dev, fault);
>> +	}
>> +
>>  	if (fault->type != IOMMU_FAULT_PAGE_REQ)
>>  		return -EOPNOTSUPP;
>>  
>> @@ -4201,6 +4220,32 @@ static void vfio_iommu_type1_notify(void *iommu_data,
>>  	wake_up_all(&iommu->vaddr_wait);
>>  }
>>  
>> +static int vfio_iommu_type1_register_handler(void *iommu_data,
>> +					     struct device *dev)
>> +{
>> +	struct vfio_iommu *iommu = iommu_data;
>> +
>> +	if (iommu->iopf_enabled)
>> +		return iommu_update_device_fault_handler(dev, ~0,
>> +						FAULT_REPORT_NESTED_L1);
>> +	else
>> +		return iommu_register_device_fault_handler(dev,
>> +						vfio_iommu_type1_dma_map_iopf,
>> +						FAULT_REPORT_NESTED_L1, dev);
>> +}
>> +
>> +static int vfio_iommu_type1_unregister_handler(void *iommu_data,
>> +					       struct device *dev)
>> +{
>> +	struct vfio_iommu *iommu = iommu_data;
>> +
>> +	if (iommu->iopf_enabled)
>> +		return iommu_update_device_fault_handler(dev,
>> +						~FAULT_REPORT_NESTED_L1, 0);
>> +	else
>> +		return iommu_unregister_device_fault_handler(dev);
>> +}
> 
> 
> The path through vfio to register this is pretty ugly, but I don't see
> any reason for the the update interfaces here, the previously
> registered handler just changes its behavior.

Yeah, this seems not an elegant way...

If IOPF(L2) enabled, the fault handler has already been registered, so for
nested mode setup, we only need to change the flags of the handler in the
IOMMU driver to receive L1 faults.
(assume that L1 IOPF is configured after L2 IOPF)

Currently each device can only have one iommu dev fault handler, and L1
and L2 IOPF are configured separately in nested mode, I am also wondering
that is there a better solution for this.

Thanks,
Shenming

> 
> 
>> +
>>  static const struct vfio_iommu_driver_ops vfio_iommu_driver_ops_type1 = {
>>  	.name			= "vfio-iommu-type1",
>>  	.owner			= THIS_MODULE,
>> @@ -4216,6 +4261,8 @@ static const struct vfio_iommu_driver_ops vfio_iommu_driver_ops_type1 = {
>>  	.dma_rw			= vfio_iommu_type1_dma_rw,
>>  	.group_iommu_domain	= vfio_iommu_type1_group_iommu_domain,
>>  	.notify			= vfio_iommu_type1_notify,
>> +	.register_handler	= vfio_iommu_type1_register_handler,
>> +	.unregister_handler	= vfio_iommu_type1_unregister_handler,
>>  };
>>  
>>  static int __init vfio_iommu_type1_init(void)
>> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
>> index a7b426d579df..4621d8f0395d 100644
>> --- a/include/linux/vfio.h
>> +++ b/include/linux/vfio.h
>> @@ -29,6 +29,8 @@
>>   * @match: Optional device name match callback (return: 0 for no-match, >0 for
>>   *         match, -errno for abort (ex. match with insufficient or incorrect
>>   *         additional args)
>> + * @transfer: Optional. Transfer the received stage/level 1 faults to the guest
>> + *            for nested mode.
>>   */
>>  struct vfio_device_ops {
>>  	char	*name;
>> @@ -43,6 +45,7 @@ struct vfio_device_ops {
>>  	int	(*mmap)(void *device_data, struct vm_area_struct *vma);
>>  	void	(*request)(void *device_data, unsigned int count);
>>  	int	(*match)(void *device_data, char *buf);
>> +	int	(*transfer)(void *device_data, struct iommu_fault *fault);
>>  };
>>  
>>  extern struct iommu_group *vfio_iommu_group_get(struct device *dev);
>> @@ -100,6 +103,10 @@ struct vfio_iommu_driver_ops {
>>  						   struct iommu_group *group);
>>  	void		(*notify)(void *iommu_data,
>>  				  enum vfio_iommu_notify_type event);
>> +	int		(*register_handler)(void *iommu_data,
>> +					    struct device *dev);
>> +	int		(*unregister_handler)(void *iommu_data,
>> +					      struct device *dev);
>>  };
>>  
>>  extern int vfio_register_iommu_driver(const struct vfio_iommu_driver_ops *ops);
>> @@ -161,6 +168,11 @@ extern int vfio_unregister_notifier(struct device *dev,
>>  struct kvm;
>>  extern void vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm);
>>  
>> +extern int vfio_iommu_dev_fault_handler_register_nested(struct device *dev);
>> +extern int vfio_iommu_dev_fault_handler_unregister_nested(struct device *dev);
>> +extern int vfio_transfer_iommu_fault(struct device *dev,
>> +				     struct iommu_fault *fault);
>> +
>>  /*
>>   * Sub-module helpers
>>   */
> 
> .
>