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

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Date:   Wed, 2 Aug 2023 07:41:05 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
CC:     "cohuck@...hat.com" <cohuck@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Duan, Zhenzhong" <zhenzhong.duan@...el.com>
Subject: RE: [PATCH v4 07/12] iommufd: Add data structure for Intel VT-d
 stage-1 cache invalidation

> From: Liu, Yi L <yi.l.liu@...el.com>
> 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?