RE: [PATCH v4 07/12] iommufd: Add data structure for Intel VT-d stage-1 cache invalidation

[Tian, Kevin]

> From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> Sent: Monday, July 24, 2023 7:13 PM
> 
> This adds the data structure for flushing iotlb for the nested domain
> allocated with IOMMU_HWPT_TYPE_VTD_S1 type.
> 
> Cache invalidation path is performance path, so it's better to avoid
> memory allocation in such path. To achieve it, this path reuses the
> ucmd_buffer to copy user data. So the new data structures are added in
> the ucmd_buffer union to avoid overflow.

this patch has nothing to do with ucmd_buffer

> +
> +/**
> + * struct iommu_hwpt_vtd_s1_invalidate - Intel VT-d cache invalidation
> + *                                       (IOMMU_HWPT_TYPE_VTD_S1)
> + * @flags: Must be 0
> + * @entry_size: Size in bytes of each cache invalidation request
> + * @entry_nr_uptr: User pointer to the number of invalidation requests.
> + *                 Kernel reads it to get the number of requests and
> + *                 updates the buffer with the number of requests that
> + *                 have been processed successfully. This pointer must
> + *                 point to a __u32 type of memory location.
> + * @inv_data_uptr: Pointer to the cache invalidation requests
> + *
> + * The Intel VT-d specific invalidation data for a set of cache invalidation
> + * requests. Kernel loops the requests one-by-one and stops when failure
> + * is encountered. The number of handled requests is reported to user by
> + * writing the buffer pointed by @entry_nr_uptr.
> + */
> +struct iommu_hwpt_vtd_s1_invalidate {
> +	__u32 flags;
> +	__u32 entry_size;
> +	__aligned_u64 entry_nr_uptr;
> +	__aligned_u64 inv_data_uptr;
> +};
> +

I wonder whether this array can be defined directly in the common
struct iommu_hwpt_invalidate so there is no need for underlying
iommu driver to further deal with user buffers, including various
minsz/backward compat. check. 

smmu may not require it by using a native queue format. But that
could be considered as a special case of 1-entry array. With careful
coding the added cost should be negligible.

Jason, your thought?