Re: [PATCH v6 2/6] iommufd: Add IOMMU_HWPT_INVALIDATE

Yi Liu
2023-12-11T07:46:40Z

On 2023/12/7 17:04, Tian, Kevin wrote:
>> From: Liu, Yi L <yi.l.liu@intel.com>
>> Sent: Thursday, December 7, 2023 2:59 PM
>>
>> On 2023/11/17 21:07, Yi Liu wrote:
>>> @@ -613,4 +614,38 @@ struct iommu_hwpt_get_dirty_bitmap {
>>> #define IOMMU_HWPT_GET_DIRTY_BITMAP _IO(IOMMUFD_TYPE, \
>>>
>> IOMMUFD_CMD_HWPT_GET_DIRTY_BITMAP)
>>>
>>> +/**
>>> + * struct iommu_hwpt_invalidate - ioctl(IOMMU_HWPT_INVALIDATE)
>>> + * @size: sizeof(struct iommu_hwpt_invalidate)
>>> + * @hwpt_id: HWPT ID of a nested HWPT for cache invalidation
>>> + * @reqs_uptr: User pointer to an array having @req_num of cache
>> invalidation
>>> + * requests. The request entries in the array are of fixed width
>>> + * @req_len, and contain a user data structure for invalidation
>>> + * request specific to the given hardware page table.
>>> + * @req_type: One of enum iommu_hwpt_data_type, defining the data
>> type of all
>>> + * the entries in the invalidation request array. It should suit
>>> + * with the data_type passed per the allocation of the hwpt pointed
>>> + * by @hwpt_id.
>>
>> @Jason and Kevin,
>>
>> Here a check with you two. I had a conversation with Nic on the definition
>> of req_type here. It was added to support potential multiple kinds of cache
>> invalidation data types for a invalidating cache for a single hwpt type[1].
>> But we defined it as reusing the hwpt_data_type. In this way, it is not
>> able to support the potential case in[1]. is it? Shall we define a separate
>> enum for invalidation data types? And how can we let user know the
>> available invalidation data types for a hwpt type? Any idea?
>>
>> [1] https://lore.kernel.org/linux-
>> iommu/20231018163720.GA3952@nvidia.com/
>>
>
> From that thread Jason mentioned to make the invalidation format
> part of domain allocation. If that is the direction to go then there
> won't be multiple invalidation formats per hwpt. The user should
> create multiple hwpt's per invalidation format (though mixing
> formats in one virtual platform is very unlikely)?

yes, following that, the hwpt data type would be a kind of a combination
of page table type and cache invalidation type. In this way, the req_type
may also be dropped as the hwpt allocation path can record the type and
reuse it in the cache invalidation path.

--
Regards,
Yi Liu