linux-kernel - Re: [PATCH v6 1/6] iommu: Add cache_invalidate

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Date:   Wed, 6 Dec 2023 14:32:09 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Yi Liu <yi.l.liu@...el.com>
Cc:     joro@...tes.org, alex.williamson@...hat.com, kevin.tian@...el.com,
        robin.murphy@....com, baolu.lu@...ux.intel.com, cohuck@...hat.com,
        eric.auger@...hat.com, nicolinc@...dia.com, kvm@...r.kernel.org,
        mjrosato@...ux.ibm.com, chao.p.peng@...ux.intel.com,
        yi.y.sun@...ux.intel.com, peterx@...hat.com, jasowang@...hat.com,
        shameerali.kolothum.thodi@...wei.com, lulu@...hat.com,
        suravee.suthikulpanit@....com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        zhenzhong.duan@...el.com, joao.m.martins@...cle.com,
        xin.zeng@...el.com, yan.y.zhao@...el.com
Subject: Re: [PATCH v6 1/6] iommu: Add cache_invalidate_user op

On Fri, Nov 17, 2023 at 05:07:12AM -0800, Yi Liu wrote:
> +/**
> + * struct iommu_user_data_array - iommu driver specific user space data array
> + * @type: The data type of all the entries in the user buffer array
> + * @uptr: Pointer to the user buffer array for copy_from_user()
> + * @entry_len: The fixed-width length of a entry in the array, in bytes
> + * @entry_num: The number of total entries in the array
> + *
> + * A array having a @entry_num number of @entry_len sized entries, each entry is
> + * user space data, an uAPI defined in include/uapi/linux/iommufd.h where @type
> + * is also defined as enum iommu_xyz_data_type.
> + */
> +struct iommu_user_data_array {
> +	unsigned int type;
> +	void __user *uptr;
> +	size_t entry_len;
> +	int entry_num;

These are u32 in the uapi, they should probably be u32 here
too. Otherwise we have to worry about truncation.

> @@ -465,6 +492,9 @@ struct iommu_domain_ops {
>  			      size_t size);
>  	void (*iotlb_sync)(struct iommu_domain *domain,
>  			   struct iommu_iotlb_gather *iotlb_gather);
> +	int (*cache_invalidate_user)(struct iommu_domain *domain,
> +				     struct iommu_user_data_array *array,
> +				     u32 *error_code);

Regarding the other conversation I worry a u32 error_code is too small.

Unfortunately there is no obvious place to put something better so if
we reach it we will have to add more error_code space via normal
extension.

Maybe expand this to u64? That is 64 bits of error register data and
the consumer index. It should do for SMMUv3 at least?

Jason