linux-kernel - Re: [PATCH v8 3/5] iommufd: Add IOMMU_GET_HW

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Date:   Thu, 17 Aug 2023 14:07:54 -0700
From:   Nicolin Chen <nicolinc@...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>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.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 v8 3/5] iommufd: Add IOMMU_GET_HW_INFO

Looks like Yi's latest code has not addressed these comments.

On Thu, Aug 17, 2023 at 07:31:42AM +0000, Tian, Kevin wrote:
 
> > From: Liu, Yi L <yi.l.liu@...el.com>
> > Sent: Wednesday, August 16, 2023 8:14 PM
> >
> > Under nested IOMMU translation, userspace owns the stage-1 translation
> > table (e.g. the stage-1 page table of Intel VT-d or the context table of
> > ARM SMMUv3, and etc.). Stage-1 translation tables are vendor specific, and
> > need to be compatible with the underlying IOMMU hardware. Hence,
> > userspace
> > should know the IOMMU hardware capability before creating and
> > configuring
> > the stage-1 translation table to kernel.
> >
> > This adds IOMMU_GET_HW_INFO ioctl to query the IOMMU hardware
> > information
> > (a.k.a capability) for a given device. The returned data is vendor
> > specific, userspace needs to decode it with the structure by the output
> > @out_data_type field.
> 
> "The format of the returned data is vendor specific and must be decoded
> according to @out_data_type field".

Ack.

> > +int iommufd_get_hw_info(struct iommufd_ucmd *ucmd)
> > +{
> > +     struct iommu_hw_info *cmd = ucmd->cmd;
> > +     void __user *user_ptr = u64_to_user_ptr(cmd->data_uptr);
> > +     const struct iommu_ops *ops;
> > +     struct iommufd_device *idev;
> > +     unsigned int data_len;
> > +     unsigned int copy_len;
> > +     void *data = NULL;
[..]
> > +     } else {
> > +             cmd->out_data_type = IOMMU_HW_INFO_TYPE_NONE;
> > +             data_len = 0;
> > +             data = NULL;
> 
> data is already initialized as NULL.

Will drop.

> > +
> > +     /*
> > +      * We return the length the kernel supports so userspace may know
> > what
> > +      * the kernel capability is. It could be larger than the input buffer.
> > +      */
> > +     cmd->data_len = data_len;
> > +
> > +     rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
> > +out:
> 
> out_free:
> 
> > +     kfree(data);
> > +err_put:
> 
> out_put: (since this is also used in the success path)

Ack for both.

> > + * To capture an iommu type specific hardware information data,
> > @data_uptr and
> > + * its length @data_len must be provided. Trailing bytes will be zeroed if the
> > + * user buffer is larger than the data that kernel has. Otherwise, kernel only
> > + * fills the buffer using the given length in @data_len. If the ioctl succeeds,
> > + * @data_len will be updated to the length that kernel actually supports,
> > + * @out_data_type will be filled to decode the data filled in the buffer
> > + * pointed by @data_uptr. Input @data_len == zero is allowed, no
> > information
> > + * data will be filled to user, but user space could get the
> > iommu_hw_info_type
> > + * filled in @out_data_type and the iommu hardware information data
> > length
> > + * supported by kernel filled in @data_len.
> 
> I'd just keep "Input @data_len == zero is allowed" and remove all the
> trailing words which just duplicate with the former context.

Will do.

> Reviewed-by: Kevin Tian <kevin.tian@...el.com>

Adding this.

Thanks
Nic