linux-kernel - Re: [PATCH 3/6] iommufd: Add IOMMU_DEVICE_GET

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Message-ID: <Y+awR7UO6R2FzHiV@nvidia.com>
Date:   Fri, 10 Feb 2023 16:59:51 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "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>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
Subject: Re: [PATCH 3/6] iommufd: Add IOMMU_DEVICE_GET_INFO

On Fri, Feb 10, 2023 at 07:55:42AM +0000, Tian, Kevin wrote:
> > From: Liu, Yi L <yi.l.liu@...el.com>
> > Sent: Thursday, February 9, 2023 12:17 PM
> > 
> > +int iommufd_device_get_info(struct iommufd_ucmd *ucmd)
> > +{
> > +	struct iommu_device_info *cmd = ucmd->cmd;
> > +	struct iommufd_object *dev_obj;
> > +	struct device *dev;
> > +	const struct iommu_ops *ops;
> > +	void *data;
> > +	unsigned int length, data_len;
> > +	int rc;
> > +
> > +	if (cmd->flags || cmd->__reserved || !cmd->data_len)
> > +		return -EOPNOTSUPP;
> 
> do we want !cmd->data_len being a way to check how many bytes are
> required in a following call to get the vendor info?

There is no reason, if the userspace doesn't have a struct large
enough then it also doesn't know what the extra bytes should even be
used for. No reason to read the.

> > +struct iommu_device_info {
> > +	__u32 size;
> > +	__u32 flags;
> > +	__u32 dev_id;
> > +	__u32 data_len;
> > +	__aligned_u64 data_ptr;
> 
> moving forward iommu hw cap is not the only information reported
> via this interface, e.g. it can be also used to report pasid mode.
> 
> from this angle it's better to rename above two fields to be iommu
> specific, e.g.:
> 
> 	__u32 iommu_data_len;
> 	__aligned_u64 iommu_data_ptr;

maybe call it hw info

Jason