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

[Shenming Lu]

On 2021/5/25 6:11, Alex Williamson wrote:
> On Mon, 24 May 2021 21:11:11 +0800
> Shenming Lu <lushenming@xxxxxxxxxx> wrote:
> 
>> On 2021/5/21 15:59, Shenming Lu wrote:
>>> 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.  
> 
> I haven't fully read all the references, but who imposes the fact that
> there's only one fault handler per device?  If type1 could register one
> handler and the vfio-pci bus driver another for the other level, would
> we need this path through vfio-core?

If we could register more than one handler per device, things would become
much more simple, and the path through vfio-core would not be needed.

Hi Baolu,
Is there any restriction for having more than one handler per device?

> 
>> Let me simply add, maybe there is another way for this:
>> Would it be better to set host IOPF enabled (L2 faults) in the VFIO_IOMMU_MAP_DMA
>> ioctl (no need to add a new ioctl, and we can specify whether this mapping is IOPF
>> available or statically pinned), and set guest IOPF enabled (L1 faults) in the
>> VFIO_IOMMU_SET_PASID_TABLE (from Eric's series) ioctl?
>> And we have no requirement for the sequence of these two ioctls. The first called
>> one will register the handler, and the later one will just update the handler...
> 
> This is looking more and more like it belongs with the IOASID work.  I
> think Eric has shifted his focus there too.  Thanks,

I will pay more attention to the IOASID work.

Thanks,
Shenming

> 
> Alex
> 
> .
>