Re: [PATCH v3 3/4] iommufd: Add IOMMU_DEVICE_GET_HW_INFO

[Baolu Lu <baolu.lu@linux.intel.com>]

On 5/15/23 2:14 PM, Liu, Yi L wrote:
>> -----Original Message-----
>> From: Baolu Lu<baolu.lu@linux.intel.com>
>> Sent: Friday, May 12, 2023 1:39 PM
>> To: Liu, Yi L<yi.l.liu@intel.com>;joro@8bytes.org;alex.williamson@redhat.com;
>> jgg@nvidia.com; Tian, Kevin<kevin.tian@intel.com>;robin.murphy@arm.com
>> Cc:baolu.lu@linux.intel.com;cohuck@redhat.com;eric.auger@redhat.com;
>> nicolinc@nvidia.com;kvm@vger.kernel.org;mjrosato@linux.ibm.com;
>> chao.p.peng@linux.intel.com;yi.y.sun@linux.intel.com;peterx@redhat.com;
>> jasowang@redhat.com;shameerali.kolothum.thodi@huawei.com;lulu@redhat.com;
>> suravee.suthikulpanit@amd.com;iommu@lists.linux.dev;linux-kernel@vger.kernel.org;
>> linux-kselftest@vger.kernel.org; Duan, Zhenzhong<zhenzhong.duan@intel.com>
>> Subject: Re: [PATCH v3 3/4] iommufd: Add IOMMU_DEVICE_GET_HW_INFO
>>
>> On 5/11/23 10:30 PM, Yi Liu wrote:
>>> Under nested IOMMU translation, userspace owns the stage-1 translation
>>> table (e.g. the stage-1 page table of Intel VT-d or the context table
>>> of ARM SMMUv3, and etc.). Stage-1 translation tables are vendor specific,
>>> and needs to be compatiable with the underlying IOMMU hardware. Hence,
>>> userspace should know the IOMMU hardware capability before creating and
>>> configuring the stage-1 translation table to kernel.
>>>
>>> This adds IOMMU_DEVICE_GET_HW_INFO to query the IOMMU hardware
>> information
>>> for a given device. The returned data is vendor specific, userspace needs
>>> to decode it with the structure mapped by the @out_data_type field.
>>>
>>> As only physical devices have IOMMU hardware, so this will return error
>>> if the given device is not a physical device.
>>>
>>> Co-developed-by: Nicolin Chen<nicolinc@nvidia.com>
>>> Signed-off-by: Nicolin Chen<nicolinc@nvidia.com>
>>> Signed-off-by: Yi Liu<yi.l.liu@intel.com>
>>> ---
>>>    drivers/iommu/iommufd/device.c          | 72 +++++++++++++++++++++++++
>>>    drivers/iommu/iommufd/iommufd_private.h |  1 +
>>>    drivers/iommu/iommufd/main.c            |  3 ++
>>>    include/uapi/linux/iommufd.h            | 37 +++++++++++++
>>>    4 files changed, 113 insertions(+)
>>>
>>> diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
>>> index 051bd8e99858..bc99d092de8f 100644
>>> --- a/drivers/iommu/iommufd/device.c
>>> +++ b/drivers/iommu/iommufd/device.c
>>> @@ -263,6 +263,78 @@ u32 iommufd_device_to_id(struct iommufd_device *idev)
>>>    }
>>>    EXPORT_SYMBOL_NS_GPL(iommufd_device_to_id, IOMMUFD);
>>>
>>> +static int iommufd_zero_fill_user(u64 ptr, int bytes)
>>> +{
>>> +	int index = 0;
>>> +
>>> +	for (; index < bytes; index++) {
>>> +		if (put_user(0, (uint8_t __user *)u64_to_user_ptr(ptr + index)))
>>> +			return -EFAULT;
>>> +	}
>>> +	return 0;
>>> +}
>>> +
>>> +int iommufd_device_get_hw_info(struct iommufd_ucmd *ucmd)
>>> +{
>>> +	struct iommu_hw_info *cmd = ucmd->cmd;
>>> +	unsigned int length = 0, data_len;
>>> +	struct iommufd_device *idev;
>>> +	const struct iommu_ops *ops;
>>> +	void *data = NULL;
>>> +	int rc = 0;
>>> +
>>> +	if (cmd->flags || cmd->__reserved || !cmd->data_len)
>>> +		return -EOPNOTSUPP;
>>> +
>>> +	idev = iommufd_get_device(ucmd, cmd->dev_id);
>>> +	if (IS_ERR(idev))
>>> +		return PTR_ERR(idev);
>>> +
>>> +	ops = dev_iommu_ops(idev->dev);
>>> +	if (!ops->hw_info)
>>> +		goto done;
>> If the iommu driver doesn't provide a hw_info callback, it still
>> returns success?
> Yes, as noted in the cover letter. It's for a remark from Jason. In such
> case, the out_data_type is NULL, it means no specific data is filled
> in the buffer pointed by cmd->data_ptr.
> 
> - Let IOMMU_DEVICE_GET_HW_INFO succeed even the underlying iommu driver
>     does not have driver-specific data to report per below remark.
>     https://lore.kernel.org/kvm/ZAcwJSK%2F9UVI9LXu@nvidia.com/

Oh, I overlooked that. Thanks for the explanation. It's fair enough.

Best regards,
baolu