linux-kernel - Re: [PATCH v4 01/17] iommu: Add hwpt_type with user_data for domain_alloc

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Message-ID: <20230925130506.GA13733@nvidia.com>
Date:   Mon, 25 Sep 2023 10:05:06 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Nicolin Chen <nicolinc@...dia.com>
Cc:     Baolu Lu <baolu.lu@...ux.intel.com>, Yi Liu <yi.l.liu@...el.com>,
        joro@...tes.org, alex.williamson@...hat.com, kevin.tian@...el.com,
        robin.murphy@....com, cohuck@...hat.com, eric.auger@...hat.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
Subject: Re: [PATCH v4 01/17] iommu: Add hwpt_type with user_data for
 domain_alloc_user op

On Thu, Sep 21, 2023 at 01:58:19PM -0700, Nicolin Chen wrote:

> Perhaps we could put all min_len defines in uAPI header, like:
> include/uapi/linux/gfs2_ondisk.h:442:#define LH_V1_SIZE (offsetofend(struct gfs2_log_header, lh_hash))
> In this way, drivers won't need to deal with that nor have risks
> of breaking ABI by changing a min_len.

I don't think we need constants, just be sure that every call to 
iommu_copy_user_data() has an offsetof() as the last parameter.

Indeed perhaps you should put it in a macro and force this to happen eg:

 #define iommu_copy_user_data(user_data, from, min_size_member) \
  __iommu_copy_user_data(user_data, from, offsetofend(typeof(*from), min_size_member))

 iommu_copy_user_data(user_data, &data, iotlb);

Jason